Name______SC_____-_____ Date ______
EXPERIMENT 9: Concentration Aim: How can we prepare solutions and dilutions and how can we tell if a salt is soluble?
In this experiment, you will learn how to produce solutions of given concentrations. Then you will mix prepared solutions to determine which ionic compounds are soluble and which are insoluble, and you will compare these results with the data in Table F.
WEEK 1: CONCENTRATIONS OF SOLUTIONS Materials: triple beam balance, 500mL Erlenmeyer flask, 250mL Erlenmeyer flask, graduated cylinder, Kool-Aid mix, beaker for weighing, spoon/scoopula, volumetric flask (teacher demo)
Part I. Stock solution of Kool-Aid
There are multiple ways to quantify the concentration of aqueous solutions. You will use molarity which is defined as moles of solute/ Liters of solution. Observe your teacher demonstrate the procedure for preparing a solution using a volumetric flask. You will prepare your solutions in a similar manner, except you will use an Erlenmeyer flask instead of a volumetric flask. AT NO POINT CAN YOU EAT THE KOOL-AID POWDER OR DRINK THE SOLUTIONS.
Your teacher will assign your group a molarity for your stock solution.
Assigned molarity of stock solution = ______M
Assume the only ingredient in Kool-Aid is sucrose, C12H22O11
1. Calculate GFM of Kool-Aid = ______g/mol [2 pts]
2. Calculate how many moles of Kool-Aid are required to make 450mL of your stock solution. Show work. [5 pts]
3. Convert the moles of Kool-Aid into grams of Kool-Aid. Show work. [5 pts]
4. Write out a detailed procedure to prepare 450mL of Kool-Aid solution with your assigned molarity using the materials listed above. Show your teacher your procedure before proceeding. [8 pts]
Instructor’s initials ______Name______SC_____-_____ Date ______
Part II. Dilution of a Stock Solution Your teacher will assign your group a molarity for your dilution.
Assigned molarity of diluted solution = ______M
5. Write out a detailed procedure to prepare 200mL of Kool-Aid solution with your assigned dilution molarity using the materials listed on the previous page. Show your teacher your procedure before proceeding. [8 pts]
Instructor’s initials ______
Part III. Comparing Concentrations 6. Examine your group’s two solutions and the solutions of the other group working at your lab table. Try to arrange all four solutions in order of increasing concentration without telling the other group the molarity of your solutions and without hearing the molarity of their solutions.
7. How can you tell which solution is the most dilute and which is the most concentrated? [4 pts]
Summary Questions 8. Define these types of solutions: Unsaturated [2 pts] Saturated [2 pts] Supersaturated [2 pts]
9. You want to test a solution to determine whether it is unsaturated, saturated or supersaturated by adding more solute to it. What would happen if the solution were: [6 pts] Unsaturated Saturated Supersaturated
10. If Kool-Aid is pure sucrose, do you expect it to conduct electricity in water? Why? [2 pts] Sugar does not form ions in solution so Kool-aid will not conduct electricity.
11. A student wants to prepare a 0.5M solution of NaCl and adds 0.25 moles of NaCl to container filled with 500mL of water What is wrong with the procedure? What should have been done instead? [6 pts]
Name______SC_____-_____ Date ______
WEEK 2: SOLUBILITY OF IONIC COMPOUNDS Materials: solutions of the salts listed in the table below in dropper bottles, plastic spot plates
In this experiment you will mix together solutions containing various different dissolved ions to determine how the solubility rules listed in Table F were created.
1. Before beginning, clean your spot plate with water. Using your dropper bottles and well plate, mix together each of the substances in the table. Look at the table below and mix one substance from the left side of the table with one substance from the top of the table. Note the five exceptions. When using your dropper bottles be sure to hold the bottle 1-2 cm ABOVE the plate so that the tip DOES NOT touch the solution in the plate – if there is contamination in the bottles you will not be able to properly determine the solubility rules.
2. In the table below, record your observations after each mixture. Be sure to note whether a precipitate is formed
NaOH CaCl2 NaI Na3PO4 AgNO3 1 2 3 4
BaCl2 5 6 7 XXXXXXXXXXXX
CuSO4 8 9 10 11
Na2CO3 12 XXXXXXXXXX XXXXXXXXXXXX XXXXXXXXXXXX
NH4OH 13 14 15 (NH3 aq) XXXXXXXXXX
3. Which ions used in compounds in this experiment dissolved without exception (always stayed in solution)? [4 pts]
4. Which ions used in compounds in this experiment precipitated without exception? [4 pts]
5. Do your results agree with the data in Reference Table F? If not, give a plausible explanation for why your results are different. [4 pts]
Name______SC_____-_____ Date ______
6. Write a balanced chemical equation for the reactions that occurred in the plates where a precipitate is formed. Use the lines below that correspond to that box number in the table on the previous page. Be sure to include the physical state of each reactant and product. [20 pts]
1 AgNO3 (aq) + NaOH(aq)→ + NaNO3(aq) 9 CuSO4(aq) + CaCl2(aq)→ CuCl2(aq) +
2 2AgNO3 (aq) + CaCl2(aq)→ + Ca(NO3)2 (aq) 10 no reaction
3 AgNO3 (aq) + NaI(aq)→ + NaNO3(aq) 11 3CuSO4(aq) + 2Na3PO4(aq)→ + 3Na2SO4(aq)
4 AgNO3 (aq) + Na3PO4(aq)→ + NaNO3(aq) 12 Na2CO3(aq) + CaCl2(aq)→ NaCl(aq) +
5 no reaction 13 no reaction
6 no reaction 14 no reaction
7 3BaCl2 (aq) + 2Na3PO4(aq)→ + 6NaCl(aq) 15 no reaction
8 CuSO4(aq) + 2NaOH(aq)→ + Na2SO4(aq)
7. Write the IUPAC names of the compounds that precipitated out of solution, using the stock method where appropriate. [5 pts]
Summary Questions
8. Compare the way salt dissolves in water to the way sugar dissolves in water. In which processes are chemical bonds broken and in which process are intermolecular attractions broken? [4 pts]
9. Draw a particle diagram of KCl dissolved in water. Be sure to include at least one water molecule with each ion showing the proper orientation of the ions and the molecule. [4 pts]
10. Suppose you wanted to prepare 25 mL of a 1.5 M solution of copper (II) sulfate pentahydrate. How many moles of the salt are needed? What is the mass in grams? Show work. [5 pts]