CH 2: General Chemistry Laboratory Department of Chemistry 1Ateneo de Manila University
Experiment 1: MEASUREMENTS PRE-LAB Study the following questions before entering the laboratory to perform this experiment.
1. What is density? Does it depend on temperature? Explain. 2. What are significant figures? What are the rules in determining and reporting the proper number of significant figures?
Things to bring: (per group of 4 – those sharing the same sink): DEGASSED regular coke and DEGASSED diet coke – open a can and leave it overnight (do not put it in the ref)
INTRODUCTION Any scientist, in the course of experimentation, must employ measurement to record his observations in the form of quantitative data, be it mass, volume, length, etc. It is the most fundamental skill that any scientist needs to acquire and master. This involves observing and recording quantitative data accurately. Accuracy means that data must be recorded truthfully and as observed or obtained (significant figures).
OBJECTIVE This experiment aims to: (a) develop in the student the skills in using the balance and graduated cylinder, (b) determine the mass, volume, and densities of Regular and Diet Coke, (c) compare their densities, and (d) demonstrate the concepts of significant figures, precision, and accuracy in measurements.
MATERIALS 10 mL Regular Coke spatula 10 mL graduated cylinder calculator sand 10 mL Diet Coke copy of the soda can labels beaker
PROCEDURE A. Measuring a desired mass of a solid substance Note: As a general rule, chemicals should never be placed directly on the balance pan. Solids may be weighed in any suitable container, such as a watch glass, a small beaker, or even a clean piece of paper. Check with your instructor regarding the suitability of each container. In future experiments, you will be expected to deduce which container is best suited for a particular measurement.
Measure the mass of a 150-mL plastic beaker (the smaller one in your locker). Record the data directly on the worksheet. Do NOT write the data anywhere else (e.g., on scratch paper or on your palm).
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Press TARE. What happens? Note down your observations.Measure 5 grams of sand. How will you do this? Do NOT put anything (e.g., a spatula) inside the sample bottle. Record the actual mass.
B. Measuring the mass and volume of liquid samples:
Weigh a dry 10-mL graduated cylinder. Press TARE. Fill the graduated cylinder with degassed Regular Coke up to the 10-mL mark. Note down the actual volume and mass of the liquid sample in the proper number of significant figures. Measure the volume of the sample at the level of the lower meniscus. Do three trials emptying and refilling the cylinder each time. You can reuse the sample; however, you CANNOT put back the sample in the reagent bottle. Afterwards, throw your liquid samples in the sink.
Repeat steps 1 and 2 using degassed Diet Coke.
Note: Degassing means removing the dissolved gas, in soda drinks it is carbon dioxide, from a solution. You can do this by opening the soda can several hours before the actual experiment. It is also recommended that you transfer the solution to a container with a larger mouth to facilitate degassing.
C. Calculating density Compute the densities of Regular and Diet Coke. Average results, NOT data. Do NOT record all the digits that show up on your calculator; record your final result in the proper number of significant figures.
References: RS Herrick, LP Nestor, & DA Benedetto. 1999. Using data pooling to measure the density of sodas. J Chem. Ed 76: 1411-1413. AMJ Javellana. 1994. Measurements. In: Simple Chemistry Experiments, 4/e. Loyola Heights, Quezon City: Philippine Institute of Pure and Applied Chemistry, pp.1-7.
2 CH 2: General Chemistry Laboratory Department of Chemistry 3Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS PART A ______
PART B ______
DATA and RESULTS
A. Mass of 150-mL beaker______Mass of the sand sample______
B. Density of Liquid samples Mass of 10 mL graduated cylinder ______
Sample Calculations:
Sample Calculations:
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QUESTIONS: 1. When using the balance, what happens if you press TARE? What is this mechanism used for? ______2. Is there a difference between the average densities of Regular and Diet Coke? If yes, what is the reason for this difference? Hint: Look for clues in the ingredients list on the product label. ______
3. If the density of water is 1.00 g/mL at the same conditions of pressure and temperature as today, which do you think will float on a basin of water—an unopened can of Regular Coke, Diet Coke, or both? Explain. ______
4. What is precision? What does it indicate? How do you evaluate precision? ______
5. What is accuracy? What does it indicate? How do you evaluate accuracy? ______
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Experiment 2: CONSERVATION OF MASS: Chemistry on the Balance
INTRODUCTION By the time you do this experiment, you will have had occasions to use the balance. The balance is one of the chemist’s most useful tools. One of the first chemists who made extensive use of this tool in his experiments was Antoine Lavoisier. As a matter of fact, everything he discovered came from “his constant and consistent use of the balance in studying chemical reactions.” (Vallarino and Quagliano) Lavoisier’s study of chemical reactions eventually led him to formulate a general statement: In any chemical reaction, the total mass of all products is equal to the total mass of all reactants. This statement is commonly called the Law of Conservation of Mass.
In this study, you will perform two experiments that resemble Lavoisier’s work, which will hopefully help you understand the Law of Conservation of Mass.
MATERIALS sodium carbonate solution calcium chloride solution sulfuric acid solution 3 test tubes 150-mL plastic beaker 10-mL graduated cylinder marker
PROCEDURE Part A 1. Measure out 4 mL of sodium carbonate into a test tube. 2. Measure out 1 mL of calcium chloride into a second test tube. 3. Place identifying mark in a third test tube and add 2 mL of sulfuric acid into it. 4. Place the three test tubes in a 150-mL beaker, making sure that the test tubes are arranged in a “balanced” manner. Record the total mass of the beaker plus the three test tubes and their contents as mr. 5. Pour all the calcium chloride solution from its test tube into the one containing sodium carbonate. Do this over the beaker to catch whatever solution might spill. Note down your observations. 6. Put back all the test tubes into the beaker, including the “empty” one. Measure the total mass of the beaker and the three test tubes and their contents. Record your measurement as mp1.
Part B 7. Remove the beaker from the balance. Hold the test tube containing the two mixed solutions with a test tube holder. Slowly and carefully add to it the sulfuric acid from the third test tube. Do this over the beaker to catch any material that might spill.
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8. Put all the test tubes back into the beaker including the two “empty” ones. Make sure that the test tubes are arranged in a “balanced” manner. 9. Measure the total mass of the beaker plus the three test tubes and their contents. Record your measurement as mp2.
CALCULATIONS 1. In step 4, the total mass mr, is the total mass of the reactants. In step 5, calcium chloride reacts with sodium carbonate to form soluble sodium chloride (which remains in solution) and insoluble calcium carbonate (which precipitates out of the solution). In step 6, the total mass after the first reaction is mp1. Calculate the difference in mass between the products and the reactants. 2. In step 7, calcium carbonate reacts with sulfuric acid to form insoluble calcium sulfate, water and carbon dioxide gas. Calculate the difference in mass between this second set of products, mp2, and the reactants.
6 CH 2: General Chemistry Laboratory Department of Chemistry 7Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS ______
D A T A & RESULTS
Sample Calculations:
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QUESTIONS 1. From your results for the difference between Mp1 – Mr, would you say that mass was conserved in the reaction? Explain why on the basis of your observations. ______
2. From your results for the difference between Mp2 – Mr, would you say that mass was conserved in the reaction? Explain why on the basis of your observations. ______
3. Why were you instructed to pour one solution into the other over the 150-mL beaker? ______
4. What do you have to do to really test the conservation of mass in step (7) of the procedure? ______
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5. Each time you poured from one test tube to another, some drops still remained in the test tube from which you poured. Does this affect your results? Explain. ______
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Experiment 3: LAYERING LIQUIDS
INTRODUCTION You will be given a set of five liquids. You are supposed to find a way of putting them in five layers, one on top of the other. To do this, you have to consider some of the properties of the substance, such as density and solubility. You know, for instance, that the denser liquid sinks and the less dense liquid floats. You must have heard of the saying that “like dissolves like”, i.e. liquids of like polarity dissolve (or are miscible) in each other. All the liquids you will be using are colorless when pure. However, some liquids have been colored to make them more visible and interesting.
MATERIALS 5 unknown liquids 10 mL graduated cylinder balance test tubes
PROCEDURE Determine the density of the five liquids. Get the mass of the dry, clean 10 mL graduated cylinder. Add approximately 2 mL of liquid to your 10 mL graduated cylinder. Record the actual volume. Get the mass of the graduated cylinder + liquid. From this data you can calculate the density of the liquid.
Using density data, you can now determine the order of the layers of the liquid. To make sure that the liquids will not mix, check their solubility in each other. Note down your observations. Once you have decided, show your procedure on how you will create the five layers to your instructor. If your plan has been approved, get 1 mL of the first liquid and carefully pour along the sides of a test tube. Then do the same for the next liquid, and so on, until you get the five layers. Show your test tube with sample to your instructor.
10 CH 2: General Chemistry Laboratory Department of Chemistry 11Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
DATA and OBSERVATIONS:
Mass of dry graduated cylinder: ______
Sample Calculations:
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Questions: 1. Do you need to test the solubility of all the liquids in each other? ______
2. How would you go about planning for seven layers of liquid? ______
3. If you use 3 mL liquid, would it affect the layers of the liquid? ______
4. What happens if you shake the layered liquids vigorously? Explain. ______
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5. What are the possible sources of errors? ______
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Experiment 4: INK/ CANDY CHROMATOGRAPHY
For Candy Chromatography: Please bring 2 packs of 2 brands of candies per group of 4.
For Ink Chromatography: Please bring 6 different types of ink pens (at least three different colors) per group of 4.
INTRODUCTION Chromatography is a well known and simple method of separating the different components of a mixture or solution. The reason why the colors in the candy coating separate has to do with the chemicals that make up the color, the solvent, and the paper. It is based on the differences in the attraction of the components of a mixture to the solvent used to separate these components. The attraction to the solvent (called eluent) may be based on one or more of several chemical properties.
For our experiment, the most important property involved is polarity (there are other properties involved, such as size and shape). The components of the colors in candy coatings are made up of pigments. These pigments have varying properties, and as such, will interact with or are attracted to the solvent in different ways. The chemicals that make up the color are called pigments.
Some of these pigments may attach better to the solvent than others, so they are carried by the solvent throughout the distance that the solvent travels, whereas others do not attach as well, and as such, are carried by the solvent to a lesser extent. The size, weight, and shape of the pigment also have something to do with how it moves along the filter paper and where it finally attaches. These factors usually cause enough separation that you can tell which colors were combined to make the original mixture.
Using paper chromatography, we will try to determine the colored components of various color-coated candies or inks. This results in enough separation of the different component pigments that you can tell which colors make up the original mixture.
OBJECTIVE To separate and identify the dyes from coated candies or inks using paper chromatography.
MATERIALS large beaker rectangular piece of filter paper
For Candy Chromatography: toothpicks 1M NaCl solution color-coated candies ( M&M’s, Skittles, Nips, Smarties, etc)
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Note: You will need two different brands, three different colors per brand. You may share packs of candy with your classmates.
For Ink Chromatography: Ethanol solution pens
PROCEDURE
A. For Candy Chromatography: Do I-III B. For Ink Chromatography: Do II-IV
I. Extraction of color from candies 1. Label each of the cups with the brand and the color of the candy. 2. Place 2-3 pieces of candy of one color into a properly labeled cup. 3. Put as few drops of water as possible in each cup to dissolve the color coating. 4. Stir carefully with the toothpick to extract as much color as possible without disturbing the white coating or the center of the candy. 5. Remove the sample as soon as the white coating appears.
II. Application of samples onto filter papers 1. Take a small piece of rectangular filter paper. Make sure that the shorter side is at least 1.00 cm shorter that the height of your beaker. Draw two horizontal lines 1.50 cm from the longer edges of the paper. Measure the distance between the two lines. This will be the distance traveled by the solvent front.
Note: Label your filter paper with a pencil.
2. Spotting (Refer to Fig. 1) a. For Candy Chromatography: Place a spot using a toothpick of each colored solution onto a designated spot on the filter paper. Repeat this 3-5 times, to the same spot, to concentrate the dye on each spot. Allow drying time between each application. b. For Ink Chromatography: Make tiny dots of each ink pen on the filter paper.
Figure 1. Spotting of ink/dye on the filter paper. 15 CH 2: General Chemistry Laboratory Department of Chemistry 16Ateneo de Manila University
3. Transfer a small amount of the 1 M sodium chloride or ethanol solution into a beaker. Keep the level of the solution below 1.5 cm. 4. Roll the filter paper into a cylinder making sure that it fits inside the beaker. Staple the ends together to stabilize the cylinder (Fig. 2).
Figure 2. Rolling of filter paper for chromatography.
5. Slowly and carefully place the paper cylinder into the beaker making sure that the bottom touches the salt or ethanol solution uniformly. Watch as the solvent front (the first line of the solvent) moves up the paper pulling along the components of the dye. 6. When the solvent front reaches the top line, remove the wet filter paper from the beaker. Air-dry the filter paper and paste it on your worksheet. Note down your observations.
III. Calculations 1. Mark out all the spots on the filter paper (chromatogram). 2. Measure the perpendicular distance from the lower line to each of the spots on the chromatogram. 3. Solve for the Retention Factor (Rf) of each spot by dividing the distance traveled by the spot over the distance traveled by the solvent front. Each spot must have its own Rf.
IV. Artwork Knowing how the different inks separate into other colored components, try to imagine a paper chromatography artwork. Sketch the image on a clean filter paper using the different pens and elute it with the solvent (II. 3-6).
REFERENCE “Colorful Candy from Science Discovery” in http://collections.ic.gc.ca/science/english/ chem/projects/chromat.html. Date accessed: 17 July 2003). “Paper Chromatography,” in http://www.ipse.psu.edu/activities/paper/ink_chromato graphy.pdf. Date accessed: 7 November 2007.
16 CH 2: General Chemistry Laboratory Department of Chemistry 17Ateneo de Manila University
Name ______Section ______Locker # ______Date ______OBSERVATIONS ______
Data and Results
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Staple your chromatogram/s here.
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QUESTIONS 1. What are dyes made of? ______
2. For each brand and color of candy/ ink, which color traveled the farthest? ______
3. Which candy/ink color had only one pigment? Which candy color/ink had many pigments/dyes? What does this tell you about the composition of the dye/pigments used? ______
4. Given the properties of your solvent and the filter paper, are the extracted pigments relatively polar or nonpolar? Explain. (Note down beside your chromatogram the order of increasing polarity of each separated pigment.) ______
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5. What complications may have arisen if you had used a ball pen instead of a pencil in labeling the filter paper? Explain. ______
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Experiment 5: FLAME TESTS
INTRODUCTION Although visually imperceptible, atoms and molecules are in constant motion. When heated, the atoms and molecules move much faster due to the energy given by the heat source. Water, for example, when heated sufficiently, turns into gas as steam.
Applying more heat to a material could sometimes cause the electrons of the atoms comprising that material to receive more energy, causing it to be promoted to a higher energy level. The Quantum Theory of the Electronic Structure of Atoms tells us that certain elements will absorb only specific quanta of energy, and this absorption is dependent on the atomic structure of that element. When a certain element absorbs a certain quantum of energy, it goes into an excited or higher-energy state. Upon its return to its ground state, the energy absorbed is emitted in the form of electromagnetic radiation, and this emission may correspond to a specific color of visible light. This promotion of the electron, and its subsequent losing of energy to return to its original energy level, gives off energy in the form of light in the visible wavelength. This phenomenon is more prevalent for the metals, since they have relatively low ionization energies making their electrons easier to move around. Since no two electrons are the same, each atom gives off a characteristic color when put into the flame.
The characteristic color that each metal produces is the basis for the qualitative determination of the presence of these elements in an unknown sample.
In this experiment, you would perform the flame test to 5 different metal salt solutions and determine the characteristic color of the flame that they produce. Also, an unknown substance similar to one of the materials that you tested will be given to you and you would have to determine which among the five it is.
MATERIALS bunsen burner test tubes nichrome wire concentrated hydrochloric acid sodium solution strontium solution barium solution calcium solution potassium solution copper solution lithium solution
Caution! Concentrated HCl is very corrosive. Avoid contact with the skin and inhalation of its fumes. Use the hood.
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PROCEDURES Take 2 mL of each solution and place them in clean test tubes. It doesn’t have to be exactly 2 mL.
Sodium is present in large quantities everywhere. It is important to ensure that no sodium particles are present during your experiment otherwise it would greatly hinder your observation of the flame colors of the other metal salts.
The flame test for sodium will give a characteristic yellow color. Most likely, putting the nichrome wire directly on the flame will produce this flame color. To clean your nichrome wire, dip it in a test tube with 2 mL of concentrated HCl, and then put the wire on the flame again. Dip the wire and put it on the flame repeatedly until the yellow sodium flame disappears.
When the wire is thoroughly cleaned, dip it into one of your metal solutions. Place the wire near the top of the flame and note down the color of the flame. Clean the nichrome wire again using the concentrated HCl solution. Do this for the other metal solutions.
When you’re done with the solutions, bring a clean test tube to the stock room to get your unknown. Again, the unknown will contain one of the five metals that you tested earlier.
Perform the flame test on your unknown solution to determine which metal is in the solution given to you. Write your observations on the Data part of your lab report.
22 CH 2: General Chemistry Laboratory Department of Chemistry 23Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
Observations ______
Data & Results
Identity of the Unknown: ______
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Questions 1. What were the difficulties you encountered in this experiment? What metal flame color was most difficult to observe? Why? Can you suggest a solution or an alternative method? ______
2. Why do you have to subject the sample to a flame? Which part of the Bunsen flame is hottest? Why was it necessary to hold the loop in this part of the flame? ______
3. What do you think will happen if you perform the flame test on a solution with more than one metal component? ______
4. Aside from the qualitative analysis of metals, state at least one other application of the flame tests. ______
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5. Will each and every metal emit a different flame test color (visible light)? Why? ______
25 CH 2: General Chemistry Laboratory Department of Chemistry 26Ateneo de Manila University
Experiment 6: Ca AND K CONTENT OF COMMON SUBSTANCES
OBJECTIVES To test the presence of Ca and K in common substances using the flame test.
MATERIALS AND EQUIPMENTS 20% KOH solution centrifuge Standard solution of Ca2+ Bunsen burner Papaya (40 g in 20 mL H2O) nichrome wire Squash/ pumpkin concentrated HCl Egg chalk Malunggay test tube Kangkong
PROCEDURE
Flame test on standard solutions 1. Dip the cleaned nichrome wire into a standard solution. Make sure a small amount of the solution is in the loop of the nichrome wire. 2. Place the loop into the hottest part of the flame. Observe the colors present.
Flame test on vegetables 1. Take a small pice of the dried vegetable using a pair of tongs. 2. Place the piece into the hottest part of the flame. Observe the colors present.
Flame test on pureed papaya 1. Fill the test tube ¾ full with pureed papaya. 2. Centrifuge the mixture for about 2 minutes. 3. Dip the clean nichrome wire into the clear liquid that was separated from the puree. 4. Place the piece into the hottest part of the flame. Observe the colors present.
Flame test on other materials (chalk, egg white, egg shell, egg yolk) 1. Place about 0.5 grams or ¼ teaspoon of material into your test tube. 2. Add about 5 mL of concentrated HCl. (Be very careful while pouring HCl, it may produce bubbles vigorously.) 3. Separate the clear liquid from the solid particles or froth by placing it into a new test tube. 4. Dip the clean nichrome wire into the clear liquid that was separated from the mixture. 5. Place the piece into the hottest part of the flame. Observe the colors present.
26 CH 2: General Chemistry Laboratory Department of Chemistry 27Ateneo de Manila University
Name ______Section ______Locker #______Date ______
DATA AND OBSERVATIONS:
Sample Observations
QUESTIONS 1. Which of the samples contain K? Which samples contain Ca? ______
2. Why is potassium important for the body? ______
Experiment 7: Preparation of a HAND CREAM 27 CH 2: General Chemistry Laboratory Department of Chemistry 28Ateneo de Manila University
INTRODUCTION Previously, most experiments have been investigations on reactions, interactions which involve the making or breaking of bonds. However there are other types of interactions which do not involve chemical transformations (bond breaking or formations). These are nonbonded interactions. Compared to bonded interactions (covalent, ionic, metallic), nonbonded interactions form weaker attractions between molecules. However, a great amount of weak forces can combine to produce strong and stable interactions.
A lot of the products that we use and the processes we employ rely on the nature of nonbonded interactions. For example, we generally use organic solvents to dissolve organic or nonpolar compounds. Most of the products we use, such as lotions, paints, etc., are in the form of stable preparations which depend on the ingredients’ nonbonded interactions.
HAND CREAM Hand creams are usually prepared as oil-in-water emulsions. An emulsion is a suspension of one liquid in a second immiscible liquid (ex. oil droplets in water). A stable emulsion is achieved in the presence of emulsifiers. Emulsifiers have hydrophobic tails and hydrophilic heads which surround suspended droplets.
There are two types of emulsions: oil-in-water and water-in-oil. If the surface tension at the interface between oil and emulsifier is greater than that between water and emulsifier, oil droplets will be formed inside a coating of emulsifiers (Oil-in-water). This is because a greater surface tension tends to require a smaller surface area. Consequently, if it is otherwise, water in oil emulsion will be formed.
To stabilize emulsions, it is necessary to agitate the mixture to break up dispersed liquid into fine droplets. The purity of water is also important since the presence of dissolved salts can break up an emulsion.
When the hand cream is applied to skin, the water evaporates leaving behind the oils and emulsifiers as a protective layer
MATERIALS Hand Cream Mineral oil Triethanolamine 2 beakers Container – to be brought by student Distilled water Preservative Stearic acid Lanolin
PROCEDURE
1. Before proceeding with the experiment, make sure your glassware, materials, and area is clean.
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2. Weigh the following into a 50-mL beaker: 0.8 g stearic acid, 0.3 g lanolin, 1.4 g mineral oil. 3. Weigh the following into another beaker: 0.2 g triethanolamine, 5 g distilled water. 4. Heat the ingredients in the first beaker until everything is just dissolved. Immediately remove from heat. Then, heat the aqueous mixture up to 90°C. Remove from heat. 5. Check the first beaker if some of the compounds has solidified. Heat the beaker again if necessary until the compounds dissolve. Remove from heat. Important: Do not boil! 6. While stirring the contents of the first beaker, pour the aqueous solution into the oil mixture. 7. Stir the mixture until room temperature. It is important to break the dispersed liquid into finer droplets so keep on stirring. 8. You can now add your favorite cologne. Five to eight drops, or a couple or more sprays, of your cologne/perfume will do. 9. Store the cream in a container and characterize.
Reference: Most, Clark F. Jr., “Nonbonded Interactions,” Experimental Organic Chemistry, (Wiley, USA: 1988), pp. 310-316.
29 CH 2: General Chemistry Laboratory Department of Chemistry 30Ateneo de Manila University
Name ______Section ______Locker #______Date ______
OBSERVATIONS ______
QUESTIONS 1. Is it possible to mix oil and water? Explain. ______
2. Is the hand cream formulation an emulsion? Explain. ______
3. If the hand cream formulation is an emulsion, which ingredient/s might possibly be the emulsifier/s? Explain in terms of chemical structure. ______
4. Give three other examples of common emulsions. ______30 CH 2: General Chemistry Laboratory Department of Chemistry 31Ateneo de Manila University
Experiment 8: CHEMICAL MASTERMIND I (& II)
INTRODUCTION You may be familiar with the game of mastermind, in which you have to guess a color sequence of pegs within a certain number of steps. In this experiment you will play the game of chemical mastermind.
Here are the rules of the game: 1. Six (or five) solutions are labeled A, B, C, D, E, F (A-E). Each solution may contain any of the following substances but you do not know which solution contains which.
For Chemical Mastermind I HgCl2 mercuric chloride Pb(CH3COO)2 lead acetate Ba(NO3)2 barium nitrate KI potassium iodide Na2CO3 sodium carbonate Ca(NO3)2 calcium nitrate
For Chemical Mastermind II KCl potassium chloride Ba(NO3)2 barium nitrate AgNO3 silver nitrate CuCl2 copper (II) chloride CuSO4 copper (II) sulfate
2. Each solution contains ions. For example, mercuric chloride contains the mercuric ion and the chloride ion. The particular solutions have been chosen such that when any two solutions are mixed, the different ions react to form a new compound. The chemical reaction is indicated by changes, such as a change in color or the appearance of a solid or both. 3. The new products may be any of the following:
For Chemical Mastermind I HgCO3 mercuric carbonate rust-colored solid HgI2 mercuric iodide orange solid PbCO3 lead carbonate white solid PbCl2 lead chloride white solid PbI2 lead iodide pale yellow solid BaCO3 barium carbonate white solid CaCO3 calcium carbonate white solid
For Chemical Mastermind II AgCl silver chloride white solid Ag2SO4 silver sulfate white solid BaSO4 barium sulfate white solid Cu2+ salts blue solution 31 CH 2: General Chemistry Laboratory Department of Chemistry 32Ateneo de Manila University
4. The object of the game is to identify the different substances A,B,C,D,E,F (A-E) by mixing the solutions together in different combinations and observing the products that form.
OBJECTIVES 1. To observe the changes that occur when certain ions react with one another. 2. To learn how to use such changes to identify ions.
MATERIALS wax paper
For Chemical Mastermind I: mercuric chloride solution lead acetate solution barium nitrate solution potassium nitrate solution sodium carbonate solution calcium nitrate solution
For Chemical Mastermind II: potassium chloride solution barium nitrate solution silver nitrate solution copper (II) chloride solution copper (II) sulfate solution
PROCEDURE 1. Take a piece of paper the same size as the wax paper. Draw a 6 x 6 (or 5 x 5) grid and label. See Data and Results for the pattern.
2. Place the wax paper over the grid you just constructed.
3. Place 1 drop of each of the 6 (or 5) unknowns in the different squares of the grid as follows: a. Put 1 drop of solution A in each square of row A (horizontal). b. Then add 1 drop of solution B in each square of row B (horizontal). c. Repeat until all the horizontal rows have been “filled” with solutions. d. Do the same thing for each vertical column.
32 CH 2: General Chemistry Laboratory Department of Chemistry 33Ateneo de Manila University
For Chemical Mastemind I:
Name ______Section ______Locker #______Date ______
On the table below, write the number of each solution on the appropriate box and list down your observations for each reaction in the corresponding cell.
RESULTS
33 CH 2: General Chemistry Laboratory Department of Chemistry 34Ateneo de Manila University
For Chemical Mastemind II:
Name ______Section ______Locker #______Date ______
On the table below, write the number of each solution on the appropriate box and list down your observations for each reaction in the corresponding cell.
CODE A B C D E A
B
C
D
E
RESULTS
Solution Code Identity (Name and Formula) A
B
C
D
E
34 CH 2: General Chemistry Laboratory Department of Chemistry 35Ateneo de Manila University
For Chemical Mastemind I/II:
QUESTIONS 1. Explain how you were able to determine the identity of your solutions. Were you able to identify all the unknowns? ______
2. What were the difficulties you encountered in conducting the experiment? ______
3. In certain cases, you do not see the expected solid in the product. Why do you think so? ______
For Chemical Mastermind II only: 4. If one of your unknowns was AgNO3 instead of Ba(NO3)2, and you were given the following descriptions: Ag2CO3 and AgCl - dirty white, AgI2 - white solid), how different will your results be? ______
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Experiment 9: BLUE PRINTING
Bring your cardboard cutouts.
INTRODUCTION Photochemistry deals with reactions which are caused to proceed more rapidly by exposure to light. A photochemical reaction begins with absorption of a quantum of radiant energy (or a photon) by the atom, ion, or molecule. The photon supplies the necessary energy to drive the reaction.
In this experiment, you will see one practical application of a redox reaction that is catalyzed by light. You will study the photochemical reaction involved in the preparation of blue printing. The process begins with the reaction of ferric ions and oxalate ions (as shown below). This reaction is caused to proceed more rapidly by exposure to light.
2+ 3- The Fe ions produced then reacts with Fe(CN)6 forming the prussian blue precipitate,
PROCEDURE
1. Make a cut-out design from an opaque cardboard material. The maximum size should be 20cm x 15cm. Note: This should be done before the lab. Be creative.
2. Mix the three solutions of FeCl3, H2C2O4, and K3[Fe(CN)6], working in an area where there is reduced light.
3. Immerse a piece of filter paper into the solution, wetting all parts thoroughly.
4. Dampen the cut-out design with tap water.
5. Put the design over the filter paper and expose to strong sunlight or UV lamp (Be cautious with regards to UV exposure)
6. When the exposed area turns blue, remove the design and immediately wash the filter paper with plenty of running water.
7. Dry and submit with the laboratory report
36 CH 2: General Chemistry Laboratory Department of Chemistry 37Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
Observations ______
Results Attach your product here.
37 CH 2: General Chemistry Laboratory Department of Chemistry 38Ateneo de Manila University
Questions 1. Which of the two reactions given above is an oxidation-reduction reaction? What is the oxidizing agent, the reducing agent? Explain. ______
2. Explain why the “covered” areas did not turn to blue. ______
3. Can reaction (2) occur even in the absence of light? Explain. ______
4. What will happen to your blueprint if it is not thoroughly washed in step 6? ______
38 CH 2: General Chemistry Laboratory Department of Chemistry 39Ateneo de Manila University
Experiment 10: pH OF COMMON SUBSTANCES AND COMPOUNDS
Bring 5 transparent common substances (liquid form) found at home, ex. Feminine wash, sprite, vinegar, solution of sugar, etc.
INTRODUCTION Many advertisements today use the term “pH”, usually accompanied by the suggestion that the pH of the advertised product is “controlled” and therefore the product is mild and safe to use.
What does the term “pH” mean? The term “pH” is a measure used to indicate just how acidic a substance or a mixture is. It is defined mathematically as the negative logarithm of the hydrogen (hydronium) ion concentration. The basis for the pH scale is the ionization of water.
Water ionizes according to the equation:
The case pf pure water, the concentration of the hydronium ion (and the hydroxide ion) is 0.0000001 M (molar or moles per liter) or 1 x 10-7 M. To simplify and avoid writing down very small numbers or exponents we can use the definition of the term “pH” to obtain the value of 7 for both the pH and pOH of pure water. The relationship between pH and hydrogen ion concentration and pOH and hydroxide ion concentration is shown in the table below.
39 CH 2: General Chemistry Laboratory Department of Chemistry 40Ateneo de Manila University
MATERIALS Test tube hydrochloric acid solutions: 1 x 10-1 1 x 10-2 1 x 10-3 1 x 10-4 1 x 10-5 1 x 10-6 sodium chloride solution 0.01 M sodium hydroxide solutions: 1 x 10-1 1 x 10-2 1 x 10-3 1 x 10-4 1 x 10-5 1 x 10-6 wide range indicator test solutions (to be announced by the Instructor)
PROCEDURE
Part 1 1. Number the test tubes from 1 to 13. Add 5 mL of each solution to each test tube as follows: to test tube 1, add the most concentrated acid; to test tube 2, the second most concentrated acid, etc. To test tube 7, add the 0.01 M NaCl solution. To test tube 8, add the least concentrated base; to test tube 9, the next least concentrated base, etc. 2. To each test tube add a few drops of indicator solution and observe the resulting color. Save the test tubes for comparison with the colors in Part II.
Part II Using the method described in Part I, determine the pH of the various substances and mixtures suggested by your Instructor.
40 CH 2: General Chemistry Laboratory Department of Chemistry 41Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS ______
DATA & RESULTS Table 1. pH of Standard Solutions
41 CH 2: General Chemistry Laboratory Department of Chemistry 42Ateneo de Manila University
Table 2. pH of Common Substances and Mixtures.
QUESTIONS 1. What is an indicator? What is it made of? ______
2. What causes the change in color of indicators? ______
3. If you are given a colored substance as a sample, how would you measure the pH of that sample? ______
42 CH 2: General Chemistry Laboratory Department of Chemistry 43Ateneo de Manila University
Experiment 11: TITRATION OF COMMERCIAL VINEGAR
PRELAB ASSIGNMENT Research on the chemistry of fermentation. Show how acetic acid is formed by this process.
Bring 25 mL vinegar samples per group.
INTRODUCTION Vinegar is prepared by fermenting sweet fruit juices (e.g. pineapple, grape, apple, sugar cane) and sap from coconut and nipa. The active component in vinegar is acetic acid, CH3COOH or HAc (where Ac = CH3COO-)
Government standards specify a minimum acetic acid concentration of 4.5% by weight or 0.75 M. To determine the acetic acid content of vinegar, it is titrated with a base of known concentration, such as NaOH sodium hydroxide. The acid-base reaction is expressed as follows:
The equation shows that acetic acid and sodium hydroxide react in equimolar (1 mole acid is to 1 mole base). If we use sodium hydroxide of known concentration, we can determine the concentration of acetic acid because we can readily determine the number of moles of sodium hydroxide needed to neutralize the acid in a given amount of vinegar sample.
MATERIALS sample of commercial vinegar 0.5 M NaOH solution phenolphthalein indicator 50-mL Erlenmeyer flask 10-mL graduated cylinder dropper bottle
PROCEDURE
Part I. Calibration of dropper Bottle 1. Fill a dropper bottle with water. 2. Fill a 10-mL graduated cylinder with water up to the 9-mL mark. 3. Bring water up to the 10-mL mark by careful addition of water from the dropper bottle. Record the number of drops used. 4. Perform 3 trials and determine the number of drops equivalent to 1 mL.
43 CH 2: General Chemistry Laboratory Department of Chemistry 44Ateneo de Manila University
Part II. Titration of Vinegar 1. Weigh a 50-mL Erlenmeyer flask. 2. Measure out 3 mL of commercial vinegar sample into the pre-weighed flask. 3. Weigh the flask and vinegar. Record the weight. Then add 1 drop of phenolphthalein. 4. Triple wash the calibrate dropper bottler with a small amount of 0.5 M NaOH. Fill the dropper bottle with the same base solution. 5. Titrate the vinegar sample with the base. Note the number of drops (volume) of base used. 6. Perform 3 trials. Use the results of the three trials to obtain the average concentration of acetic acid in the vinegar sample.
CALCULATIONS 1. Calculate the concentration (molarity) of acetic acid in your vinegar sample. (Macid)(Vacid) = (Mbase)(Vbase)
2. Calculate the percentage of acetic acid in 3 mL vinegar sample.
% HAc = {(M base )(V base )} x MW of acetic acid x 100 Weight vinegar sample
44 CH 2: General Chemistry Laboratory Department of Chemistry 45Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS ______
DATA & RESULTS
Sample Calculations
45 CH 2: General Chemistry Laboratory Department of Chemistry 46Ateneo de Manila University
QUESTIONS 1. Why did you need to calibrate your dropper bottle? ______
2. What do you observe when you do not swirl the solution after adding several drops of NaOH? ______
3. From your results, does the vinegar conform to government standards? Compare your results with others who analyzed the same sample. What conclusions can you make out of this? ______
4. What are the possible sources of error in this experiment? ______
5. Would the reported molarity of the vinegar sample be affected by an error in weighing? How about the % HAc? ______
46 CH 2: General Chemistry Laboratory Department of Chemistry 47Ateneo de Manila University
6. Compare different brands of vinegar used in class. Which has the highest concentration of acetic acid? the lowest? ______
47 CH 2: General Chemistry Laboratory Department of Chemistry 48Ateneo de Manila University
Experiment 12: Make your own ICE CREAM
Note: This lab activity is to be done in groups of 4 (those sharing a sink)
BRING THE FOLLOWING MATERIALS TO CLASS: a. One empty cylindrical 1-gallon ice cream container with cover, preferably made of plastic b. One (1) SMALL cylindrical metal container with cover that will fit inside the large container (ex. 1-pint can or the cup sized can, not half-gallon can). Make sure that the cover fits well and that the material of the container does not easily break. The material should preferably be metallic or anything not too thick to allow for easier cooling. c. ZIP-LOCKS – we’ll try using this too. SO bring ziplocks of two sizes. d. packing tape / duct tape (This will be used to seal both the large and small containers so make sure you have enough) e. at least 1 kg of rock salt f. rags and tissue (to wipe wet surfaces) g. spoons, cups and other utensils which you may need (for taste testing the ice cream) h. all of the necessary equipment you will need to prepare your ice cream mixture (e.g. measuring cups, measuring spoons, beaters, mixing bowls, etc.) i. ingredients j. extra ice k. extra stuff for garnish/decorating etc.
RECIPE - 1.5 cups all-purpose cream - 1.5 cups evaporated milk - ¾ cup confectioner’s sugar - To enhance the flavors you can do the following revisions:
VANILLA – add vanilla extract CHOCOLATE / MELON / STRAWBERRY – use flavored milk or add chocolate / strawberry syrup to the mix COOKIES & CREAM – add vanilla extract and ground Oreo cookies ROCKY ROAD – use chocolate milk or add chocolate syrup; add marshmallows
NOTE: You are not limited to this recipe. There are a lot of other ice cream recipes available on the Net. Avoid recipes that use raw egg. BE CREATIVE AND ADVENTUROUS WITH YOUR FLAVORS!
PREPARATION a. Prepare your ice cream mixture. Please limit the amount you are going to prepare to the capacity of your small container. b. Mix everything well then pour into the small container.
48 CH 2: General Chemistry Laboratory Department of Chemistry 49Ateneo de Manila University c. Cover the small container then secure the lid using packing tape / duct tape. Make sure that container is well sealed so that none of the salt and ice water will leach into your ice cream mixture. (No one wants salty ice cream.) d. Place the sealed small container into the larger container. Pack with alternate layers of ice and rock salt. Do not scrimp on the salt. The more you add, the faster you will finish churning. e. Cover the larger container then secure with tape as you did with the small container. f. Spend 30-40 minutes (or more if necessary) rolling the can to ensure even crystallization of the ice cream mixture. You can check occasionally if the ice has melted inside the large container. Top up with more ice and salt if necessary g. Show your product to the instructor. Taste your ice cream.
49 CH 2: General Chemistry Laboratory Department of Chemistry 50Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
Product Name: ______
Recipe:
50 CH 2: General Chemistry Laboratory Department of Chemistry 51Ateneo de Manila University
Experiment 13: COPPER INTO GOLD: The Alchemist’s dream INTRODUCTION
Alchemy is usually defined as the art of transmuting base metals into gold. The earliest alchemists were indefatigable laboratory workers who tried to carry out processes predicted by their theory and to speed the action of nature by which, over a long interval of time, gold was perfected deep in the earth. By the application of various types of heat and by the use of various reagents, they hoped to produce gold as good as that furnished by nature, and in much less time.
A mixture of zinc dust and sodium hydroxide is heated in an evaporating dish. They react to form sodium zincate: - + [Zn(OH) (H2O)] Na
A copper loop is then placed under the surface of the sodium zincate solution and heated. This results in the plating of zinc onto the copper loop. The loop is then heated and it turns to “gold” as a result of the formation of the brass alloy.
MATERIALS Zinc dust Evaporating dish 6 M NaOH solution Tripod 1 m H2SO4 solution Bunsen burner Copper wire coil Tissue paper Crucible tongs Wire gauze
PROCEDURE 1. Measure out approximately 5 grams of zinc dust in an evaporating dish and add enough NaOH solution to cover the zinc and fill the dish one-third. 2. Place the dish on a wire gauze and heat until the solution is nearly boiling. 3. Clean a copper coil thoroughly with fine sand paper. 4. Using crucibles, place the cleaned coil in the mixture in the dish. Leave the loop until the silver-colored coating is complete. 5. Remove the loop, rinse it with water and dry with tissue but DO NOT RUB. Remove all particles of zinc. 6. Using the tongs, heat the loop on the hot wire gauze. The gold color appears immediately. When it does, remove the loop, rinse and dry. 7. SPECIAL DISPOSAL PROCEDURE: do not discard the waste zinc in the trash container. When it dries, it forms a powder that may spontaneously ignite. Rinse the NaOH-Zinc mixture several times with water. Then add the solid to a beaker that contains 200 mL of 1 M sulfuric acid. When all the solids dissolve, flush the solution down the drain with plenty of water.
51 CH 2: General Chemistry Laboratory Department of Chemistry 52Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS ______
D A T A & RESULTS Attach your loop here. Be creative in shaping the loop.
52 CH 2: General Chemistry Laboratory Department of Chemistry 53Ateneo de Manila University
QUESTIONS 1. Define plating. ______
2. What is an alloy? ______
3. Why did the loop turn silver in color? ______
4. Why did the silver-colored loop turn gold in color? ______
5. Why do we need to heat the silver-colored loop to turn it gold? ______
53 CH 2: General Chemistry Laboratory Department of Chemistry 54Ateneo de Manila University
Experiment 14: TIE DYE
Pre-caution
Choose a cotton garment, or sheet to dye. If you mix very fine powder dyes with water, protect your lungs with surgical mask or filter over your mouth and nose. To protect your eyes from dust, use protective goggles.
Materials
100 % cotton T-shirt, apron or fabric (to be brought by students) Rubber gloves (to be brought by students) Biggest Selecta ice cream container for soaking garments (to be brought by students) A 12-inch or longer dowel 3-6 packs of dye ( to be brought by the student) Rubber bands Scissors Soda Ash Paper towels, cardboard or newspaper Nonchlorine, nonbleach laundry detergent
Procedure Tip: Lay cardboard, plastic or newspaper on the floor or table where you’ll be working to protect all surfaces from dyes that may splash. Wear old clothes when you tie-dye, in case you accidentally spill some dye on yourself.
1. Pre-treat your garment to get the best and quickest bond with the dye. Put on rubber gloves and mix a few teaspoons of Na2CO3 into warm water (150mL). Submerge your fabric in this mixture, and let it soak for 15 minutes. 2. After soaking, remove the fabric form the solution and wring it out. 3. Mix 3 packs of dye in 1.2 L H2O, boil the soil.
For spiral design: Tip: Material can be protected from the dye by tightly scrunching, twisting and/or sewing up certain parts.
1. Lay the damp, pre-treated fabric (apron or T-shirt) flat on your working surface, face up and smooth out all the wrinkles. 2. Take a dowel and place the tip of it on the fabric where you want the center of the spiral. 3. While keeping the firm pressure on the dowel’s tip, turn it counterclockwise to gather up the material around the dowel. 4. The material will begin to bunch up around the dowel in pleats. Keep the pleats form climbing up the dowel by flattening them with your hand. As you flatten the pleats, keep them from becoming too fat by creating new pleats within the pleats, thus creating a kind of whirlpool effect in the fabric.
54 CH 2: General Chemistry Laboratory Department of Chemistry 55Ateneo de Manila University
5. Continue to twist the dowel and flatten the material while refining the pleats, until you have what looks like a cinnamon roll. 6. Take three rubber ands and secure the cinnamon roll-like fabric with them. Place the rubber bands so that they evenly divide the rolled-up fabric, like a freshly cut pie. 7. The six ‘slices’ that the three rubbers create make natural guidelines for dying the fabric. 8. Soak the fabric into a tub of boiling water with dye. 9. Boil the fabric for 10 minutes. 10. Add 2 teaspoons of NaCl and boil for another 20 minutes. 11. Let the fabric soak in the dye solution for 90 minutes. 12. Removed the bundled fabric form the solution and wash with cold running water to remove the excess dye. 13. Rinse the fabric and hang to dry. Enjoy.
Reference: “Tie Dye and Other Hippie Art,” in http://www.artsandmusicpa.com/popculture/tie dye.htm. Date accessed: 30 March 2006.
55 CH 2: General Chemistry Laboratory Department of Chemistry 56Ateneo de Manila University
Experiment 15: Preparation of an ANTICHAP LIPSTICK
Introduction
For the preparation of the lipstick, you will mix a variety of hydrophobic compounds, mostly waxes and oils. When heated, these compounds blend and are held together through similar attractive forces. Like bonded interactions, non-bonded interactions generally follow the rule of thumb: ‘Like dissolves like.’
Materials
Wide watch glass Container (empty lipstick tube) - to be brought by the student Beaker Stirring rod
Chemicals
Carnauba Wax Beeswax Anhydrous Lanolin Acetyl alcohol Castor oil Old lipstick (to give color to lip balm) - optional Menthol - optional Preservative – optional
Procedure Tip: Before proceeding with the experiment, make sure that your glassware, materials, and working area are clean.
1. Weigh the following into a watch glass: 0.2 g carnauba wax, 0.8g beeswax, 0.3g lanolin, 0.3 g acetyl alcohol, 3.1 g castor oil. 2. Heat the ingredients over a steam bath until everything has dissolved. 3. Add about two spatula points of menthol. 4. Color can be added to the lipstick by mixing a small amount of the old into the mixture. 5. Stir until mixture is homogenous. 6. Using tongs pour the mixture into a clean, empty lipstick tube and let it cool. 7. When a ‘tunnel’ formed in the center as the mixture cools, fill this with more of the melted mixture. 8. You can pass the tip over an open flame to get that glossy look most lipstick have (This process is called flaming.).
56 CH 2: General Chemistry Laboratory Department of Chemistry 57Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS ______
DATA & RESULTS
57 CH 2: General Chemistry Laboratory Department of Chemistry 58Ateneo de Manila University
QUESTIONS 1. Enumerate all the nonbonded interactions you have encountered. Explain each briefly. ______
2. Why would the presence of ions in the mixture disrupt the stability of emulsion? ______
3. A lipstick is just an artificial lipid layer. What is the use of this artificial lipid layer to your lips? ______
58 CH 2: General Chemistry Laboratory Department of Chemistry 59Ateneo de Manila University
Experiment 16: HIDDEN SUGAR
Introduction
Carbohydrates are substances, which contain carbon, hydrogen, oxygen and occasionally nitrogen. Together with fats and proteins, carbohydrates make up one of the three most important classes of compounds in living systems. Carbohydrates are the most abundant constituents of many foods. The Filipino diet consists of approximately 70-80% carbohydrates. The simplest carbohydrates are known as monosaccharides. Examples include glucose and fructose. When two simple sugars are joined, the resulting product is a disaccharide. Examples of disaccharides include sucrose, maltose and lactose. A large number of monosaccharide joined together is called a polysaccharide. Starch and cellulose are examples of polysaccharides.
Material
Bring five food and /or beverage samples that are labeled ‘sugar free’.
Procedure
1. Dissolve a pinch of the sample in 3 mL distilled water in a test tube. Make sure the resulting mixture is colorless. Dilute colored solutions to almost colorless, if necessary. 2. Pour 3 mL of Benedict’s solution. 3. Heat test tube for 2 minutes. The product of a green, yellow or red precipitate indicates a positive reaction for reducing sugar.
59 CH 2: General Chemistry Laboratory Department of Chemistry 60Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS
Sample Observations Positive/negative
QUESTIONS 1. Which of the “sugar-free” food samples contained sugars? ______
2. Look at the ingredients list of the food samples. Which substances serve as the sugar substitute? ______
60 CH 2: General Chemistry Laboratory Department of Chemistry 61Ateneo de Manila University
Experiment 17: Crystal Making
Introduction Snowflake (Fig. 1), diamond and salt are some of the crystals found in nature. According to Webster, a crystal is a body that is formed by the solidification of a chemical element, a compound, or a mixture and has a regular repeating internal arrangement of its atoms and often external plane faces. In nature, crystals are formed from molten rocks. Well-formed crystals can be spectacular in form and color, an example is the diamond which is known as the hardest naturally occurring stone valued for its hardness and rarity. But other than jewelry, crystals can be found in various applications. Quartz (SiO2) crystals are used as frequency generators in electronic applications; calcite (CaCO3) crystals are used as polarizer for light waves in microscopes; and silicon (Si) crystals as starting material for computer chips.
Figure 1. A real snowflake (Image taken from ref. # 1).
Believe it or not, crystals can also be grown in the laboratory. Crystallization is the process of forming solid crystals from a melt. The substance to be crystallized is dissolved and allowed to slowly form into solid crystals as the solvent gradually cools and evaporates. From the dissolved form, the substance is transformed into a crystal form, which grows as more of the solvent evaporates. The decrease in temperature also helps in forming the crystal since the solubility (or the susceptibility of the substance to be dissolved in the solvent) lowers with decreasing temperature. Thus, a spoon of sugar is more easily dissolved in a cup of hot water than in cold water of the same amount. Enough time should be given for the atoms/molecules to selectively build up and form the basic pattern that gives the crystal its shape.
In this experiment, we will make crystals of alum.
Materials
Clean glass jar (small) Fishing line (string) - to be brought by the student Popsicle stick – to be brought by the student Beaker for boiling water and making solution Stirring rod
Chemicals
Alum [KAl(SO4)2·12 H2O] Distilled Water 61 CH 2: General Chemistry Laboratory Department of Chemistry 62Ateneo de Manila University
Procedure
FYI: Alum is non-toxic. Alum solutions can cause eye irritation. Wear goggles or safety glasses when working with the solution.
Making the seed (or “baby”) crystal 1. Weigh out approximately 5 g of Alum. 2. Place the alum into a clean 250-mL beaker. 3. Add 12 mL of water and heat the mixture to approximately 600C. 4. Stir until all the alum has dissolved.
Tip: If the mixture remains cloudy, let it stand for a few minutes to allow the suspended matter to settle. Carefully decant the clear solution into another clean vial. If necessary, heat the mixture, briefly, to complete solution of the alum crystal.
Figure 2. Set-up for suspending a thread into the solution (Image taken from ref. # 3).
5. Tie a piece of thread to the cap of a vial. Adjust the length of the thread so that not more than ½ inch (1.3 cm) is submerged (Fig. 2). 6. Smear mineral oil on the part of the thread above the solution to prevent the solution from creeping up the thread. If fishing line is used, no need to smear mineral oil. 7. Transfer the warm alum solution into the vial. 8. Place the cap on the top of the vial, cover and store in a safe place. 9. Crystals should form on the submerged thread, at the bottom of the vial, or in both places within a few days or by the end of one week.
Picking the crystals 1. Remove the thread form the solution. Remove all the crystals except the best formed one from the string. 2. If a suitable crystal has not formed on the string, decant the solution form the crystals at the bottom of the beaker into a lean container. Inspect the crystal and select one that has a regular octahedral shape and smooth faces. 3. Pick out the best crystal and loop a fine thread around the selected crystal and tie it with a knot. Save several of the remaining crystals as reserve, in case anything happens to your choice seed crystal.
Tip: Wrap the reserve crystals in a plastic wrap or place in a small plastic bag to keep them from drying.
62 CH 2: General Chemistry Laboratory Department of Chemistry 63Ateneo de Manila University
After one week or so……
Figure 3. Formation of a crystal at the thread end (Image taken from ref. # 3).
Growing the crystal 1. Dissolve 5 g of alum in 12 mL of water, heating to about 600C. If all the alum does not dissolve, you may have to add a minimum amount of water.
Tip: Add 2 mL of water and warm the solution back to about 600C. Add water in 1 mL increments, warming the solution between additions, until all the alum dissolves. Dilute solutions will not give crystals.
2. Allow this solution to cool to room temperature. 3. Suspend your choice seed crystal in the cool solution, cover the vial with cap.
Tip: If your solution is not saturated at the time you add your seed crystal, the crystal will begin to dissolve and maybe lost. To prevent such an undesirable occurrence, observe the solution in the vicinity of the seed crystal after its placement into the solution. Should the solution be unsaturated, causing the crystal to begin to dissolve, the part of the solution in contact with the crystal will become more concentrated and denser more remote from the crystal. The denser solution will flow toward the bottom of the beaker. Should you see such a density current, remove the seed crystal, cool the solution further, dissolve more alum, or let the solution sit undisturbed for about a day to allow for some evaporation of the water.
4. Inspect the alum crystal and solution on a regular basis. If the crystal has stopped growing, and other crystals have formed on the bottom of the solution, remove the crystal and warm the solution to dissolve the additional crystals. If necessary, add small amounts of water (about 1 mL) and warm until all the crystals dissolve. Cool the solution and add the large crystal.
Disposal The materials used in this experiment are non-toxic and can be safely disposed of in the trash or liquids can be poured down the drain.
Reference: 1. “Merry Christmas,” in http://www.marginalrevolution.com/photos/uncategorized/snowflake1_1.jpg. Date accessed: 7 November 2007
63 CH 2: General Chemistry Laboratory Department of Chemistry 64Ateneo de Manila University
2. Bartholomew, Dwight U., “How to grow your own crystals,” in http://www.geocities.com/rainforest/canopy/2525/crystals/. Last updated:16 Feb 2001. Date accessed: 7 Nov 2007. 3. www.chymist.com/alum%20crytals.pdf . Date accessed: 2 April 2007.
64 CH 2: General Chemistry Laboratory Department of Chemistry 65Ateneo de Manila University
Name ______Section ______Locker # ______Date ______
OBSERVATIONS
(Record your observations in preparing and operating your alum crystal(s). Include the description of the stages of the crystal growth.) ______
DATA & RESULTS
Record all the necessary data obtained for this experiment.
Mass of final alum crystal(s): ______g 65 CH 2: General Chemistry Laboratory Department of Chemistry 66Ateneo de Manila University
Draw a diagram of your crystal (or one of the smaller crystals if you do not have a large one).
66 CH 2: General Chemistry Laboratory Department of Chemistry 67Ateneo de Manila University
QUESTIONS 1. What is a saturated solution? What is a supersaturated solution? Explain the formation of crystals in light of these two kinds of solutions. ______
2. What are the two types of nucleation (or formation of seed crystal)? Why does the seed crystal form at the end of the thread? ______
3. What are the uses of alum? ______
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