DOCSLIB.ORG

H2ovsh2o2chemicalproperties

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Grade Level/Course: Science 8 / Physical Science Lesson/Unit Plan Name: H2O vs. H2O2: Chemical Properties and Formulas Rationale/Lesson Abstract: This lesson will demonstrate some of the differences in chemical properties between water (H2O) and hydrogen peroxide (H2O2), as well as provide an example to begin understanding how chemical formulas are written. Extensions can include designing an experiment to test an effect, chemical bonds, rearrangement of atoms in reactions, as well as balancing equations. Timeframe: 2+ class periods Standard(s): CST standard: REACTIONS 5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept: a. Students know reactant atoms and molecules interact to form products with different chemical properties. b. Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same. c. Students know chemical reactions usually liberate heat or absorb heat. NGSS: MS: CHEMICAL REACTIONS Disciplinary Core Ideas PS1.A: Structure and Properties of Matter § Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it. (MS-PS1-2) PS1.B: Chemical Reactions § Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. (MS-PS1-2),(MS-PS1-5) § The total number of each type of atom is conserved, and thus the mass does not change. (MS-PS1-5) § Some chemical reactions release energy, others store energy. (MS-PS1-6) Page 1 of 12 WCCUSD 11/07/14 Instructional Resources/Materials: Activities may be done as demonstrations for class, or in groups. Food color activity: • Food coloring • Tap water • Hydrogen peroxide • 2 x 250mL beakers Meat activity • small samples of ground beef • 2 x small petri dish or Dixie cup • Tap water • Hydrogen peroxide ‘Elephant toothpaste’ • Empty plastic bottle, 1-2 liter, or large Erlenmeyer flask • Food coloring—blue is nice for this. • Dish soap • Warm tap water • Active dry yeast, (1/2 packet per demo) • 2 x 250 mL beakers • Hydrogen peroxide (6% “20-volume developer”, or 12% “40 volume developer” from a beauty supply store work best for this demo!) • Safety goggles • Metal/plastic tray or newspaper to catch eruption (for easier clean up) Chemical Formula activity • Wooden molecule model sets (or Dots candy and toothpicks) Handouts included below: • Understanding Chemical Formulas • Molecule Models • (extension) Balancing Equations Page 2 of 12 WCCUSD 11/07/14 Activity/Lesson: Background Information The chemical formula for water is H2O. The chemical formula for hydrogen peroxide is H2O2. Though the formulas and physical appearance may seem similar, they are completely different substances, with different chemical properties. The activities and demonstrations in this lesson offer evidence of this fact. For your lab activities and demonstrations, hydrogen peroxide is available in several concentrations. The typical hydrogen peroxide found in grocery and drug stores is 3% H2O2. Beauty supply stores carry “hair developer” called 20-volume (6% H2O2), or 40-volume (12% H2O2). It is even possible to acquire 30% H2O2, but it can present some dangers for untrained presenters. The lab activities and demonstrations provided here demonstrate the decomposition reaction: H2O2 à H2O + O2. Students will observe the release of oxygen—bubbling from meat, and foam in elephant toothpaste. Warm Up / Do Now Fill one beaker with a small amount (≈100mL) of water and the other beaker with an equal amount of hydrogen peroxide. 1. Describe the physical properties of Beaker 1—Water, and Beaker 2—Hydrogen peroxide. Responses may include: both are liquid, clear, colorless, odorless, similar viscosity, etc. 2. Describe what difference you see in the chemical formulas of water (H2O) and hydrogen peroxide (H2O2). Responses may include: Hydrogen peroxide has one more oxygen atom, or an extra ‘O’, or hydrogen peroxide is bigger, or has more atoms, etc. Page 3 of 12 WCCUSD 11/07/14 Activity/Lesson continued: After discussing Warm Up, continue using the same two beakers for Activity 1. The three activities may be demonstration or in groups of students. Activity 1—Food coloring Squeeze one drop of food coloring into each beaker. Do not stir. Students write down observations and differences. (Students should observe that in water, the drop sinks, and spreads slowly. In hydrogen peroxide, the drop will sink and then come up to the surface. The color will spread out mostly on the surface.) Activity 2—Ground beef Place a small bit of ground beef into two small dishes or Dixie cups. Pour water into one cup, covering the meat. Pour hydrogen peroxide into the other cup, covering the meat. Students write down observations and differences. (Students should observe that in water, nothing observable happens. The meat gets wet. However, in hydrogen peroxide, bubbles begin to form around the meat, and soon the solution becomes foamy with bubbles.) Activity 3—‘Elephant toothpaste’ • Quantities that follow are appropriate for a 2-liter bottle container. These can easily be reduced for smaller 500mL water bottles, for example. • Hydrogen peroxide can stain clothes. • Wear safety goggles. • TEST IT ON YOUR OWN BEFORE DOING THIS WITH STUDENTS! Procedures 1. Warm up ≈50mL of water in a beaker to activate the yeast. The water should be ≈100°F, or about what comes out of the hot water tap. 2. Pour in ≈5mL (or ≈1 tsp, or ½ packet) of dry active yeast. Swirl to mix. Let sit a few minutes. 3. Measure out in a beaker ≈125 mL of 12% hydrogen peroxide (‘40-volume hair developer’). 4. Set the 2-liter bottle onto the tray or newspaper. 5. Pour the hydrogen peroxide into the 2-liter bottle. 6. Squeeze in a little dish soap into the 2-liter bottle, say, 10-15mL. 7. Squeeze plenty of food color, several drops, in to the 2-liter bottle. 8. Swirl the 2-liter bottle around to mix the hydrogen peroxide with the soap and color. 9. Ready? Pour the beaker of water and yeast into the 2-liter bottle. 10. Stand back and watch! Students write down observations. (Students should notice rapid eruption of foam, and some heat coming from foam. Bottle will be warm as well.) Page 4 of 12 WCCUSD 11/07/14 Extension Students can use this demonstration, and turn it into an experiment: Ask: “What could you change in this experiment to affect what happened?” Examples might include: changing amount of yeast or water or hydrogen peroxide, different temperatures of water or hydrogen peroxide, different size or shape of container, etc. Students can make a hypothesis, test, measure, record results, make a conclusion, communicate results, etc. Chemical Properties Why do we observe different chemical properties between water and hydrogen peroxide? Although their physical appearance is similar, and the chemical formulas (H2O and H2O2) look similar, they are different substances with different chemical properties. They will behave differently in the same situation. Similarly, even though water and hydrogen peroxide are made of the elements hydrogen and oxygen, when the atoms of those elements are bonded together, they have new, different properties from when the elements are uncombined. What’s happening? The bonds between the oxygen atoms in H2O2 are fairly weak, so they tend to break apart on their own, in what is called a ‘decomposition’ reaction. The bonds that hold H2O2 together break apart and the atoms are rearranged to form water (H2O) and oxygen (O2) molecules. This happens slowly in store-bought hydrogen peroxide, so even in dark bottles, it will ‘expire’ in a year, or less if it’s opened. The yeast in our demonstration acts as a catalyst to speed up this reaction. And higher concentrations of H2O2 produce more oxygen. Why is it warm? Chemical reactions involve energy. Sometimes the energy produced by the reaction is more than what goes into making the reaction happen. When that happens, energy is released, usually as heat, and it is called an “exothermic” reaction. Other examples of exothermic reactions include burning (or combustion) and glow sticks. The opposite can also happen, where energy is absorbed, like in instant cold packs or photosynthesis. These reactions are called “endothermic”. Page 5 of 12 WCCUSD 11/07/14 Chemical Formulas Looking at the difference between water (H2O) and hydrogen peroxide (H2O2) offers a good introduction to how chemical formulas are written. The subscript is the smaller number to the lower right of each symbol. The subscripts show the number of atoms in each molecule of the compound. Where there is no number, one atom is implied. For example, in each molecule of ferric chloride: FeCl3, there is one atom of iron (Fe) and three atoms of chlorine (Cl). You try: Describe which elements and how many atoms are in each molecule of CO2 (carbon dioxide). “There is one carbon atom and two oxygen atoms in every CO2 molecule.” You try: What elements are in Na2S3 (disodium trisulfide), and how many atoms of each element are in each molecule? “There are two sodium atoms and three sulfur atoms in every molecule.” Parentheses are used in chemical formulas for groups of atoms that appear together multiple times in a molecule. For example, in calcium phosphate: Ca3(PO4)2 , there are two groups of phosphate (PO4) in each molecule. A coefficient shows the number of whole molecules in a formula. In a chemical equation, it shows the ratio of molecules present in the reaction. Similar to a coefficient in math, it multiplies all that comes after it.
Recommended publications
  • Introduction to the Preparation and Properties of Hydiogen Peroxide

    Introduction to the Preparation and Properties of Hydiogen Peroxide

    CHAPTER 1 Introduction to the Preparation and Properties of Hydiogen Peroxide 1 Introduction The following chapter will discuss the preparation of hydrogen peroxide, historically, the present day and future vistas for its in situ preparation. A brief introduction to the physical properties of hydrogen peroxide will also be made for the sake of completeness. Finally, the chapter will conclude with a practical approach to the safe handling of peroxygen species, destruction of residual peroxygens, and the toxicological and occupational health considerations required when handling hydrogen peroxide. 2 Industrial Manufacture of Hydrogen Peroxide The industrial manufacture of hydrogen peroxide can be traced back to its isolation in 18 18 by L. J. Thenard. Thenard reacted barium peroxide with nitric acid to produce a low concentration of aqueous hydrogen peroxide; the process can, however, be significantly improved by the use of hydrochloric acid. The hydrogen peroxide is formed in conjunction with barium chloride, both of which are soluble in water. The barium chloride is subsequently removed by precipitation with sulfuric acid (Figure 1.1). Hence, Thenard gave birth to the first commercial manufacture of aqueous hydrogen peroxide, although it took over sixty years before Thenard’s wet chemical process was employed in a commercial capacity.2 The industrial production of hydrogen peroxide using the above route was still operating until the middle of the 20th century. At the turn of the 19th century, approximately 10000 metric tonnes per annurn of barium peroxide were converted to about 2000 metric tonnes of hydrogen peroxide. Thenard’s process has, however, some major drawbacks which quenched the expectant explosion of its use in an aqueous form.
  • Preparing to Manufacture Hydrogen Peroxide

    Preparing to Manufacture Hydrogen Peroxide

    PREPARING TO MANUFACTURE HYDROGEN PEROXIDE Part of the Hydrogen Peroxide Propulsion Guide The early laboratory preparation of hydrogen peroxide was based on the technique that Thenard used during the initial preparation of hydrogen peroxide. In this technique, barium nitrate, purified by recrystallization, was decomposed by heating in air in a porcelain retort. The resulting oxide was further oxidized by heating in a stream of oxygen to a dull red heat. The barium peroxide which formed was then dampened, ground, and dissolved in hydrochloric acid (nitric acid was used in Thenard’s initial experiments). A slight excess of sulfuric acid was then added to precipitate barium sulfate and regenerate hydrochloric acid. The procedure of barium peroxide solution and sulfate precipitation was repeated several times in the same solution to increase the peroxide concentration (concentrations of up to 33 percent by weight hydrogen peroxide could be achieved in this manner). The concentrated solution containing water, hydrogen peroxide, and hydrochloric acid, along with accumulated impurities, was cooled with ice and saturated with barium peroxide; iron and manganese impurities in the solution were then precipitated out as phosphates. The hydrochloric acid was removed by the addition of silver sulfate and the sulfate ion was removed by the subsequent addition of barium oxide. Further concentration was accomplished by vacuum distillation until “no further density increase occurs.” Thenard reported that 100 w/o hydrogen peroxide (on the basis of density data and the measurement of the volume of oxygen released) could be obtained by this technique. The first record of commercial production of hydrogen peroxide appeared in the 1865 to 1875 period.
  • Chapter 20 Electrochemistry

    Chapter 20 Electrochemistry

    Chapter 20 Electrochemistry Learning goals and key skills: Identify oxidation, reduction, oxidizing agent, and reducing agent in a chemical equation Complete and balance redox equations using the method of half-reactions. Sketch a voltaic cell and identify its cathode, anode, and the directions in which electrons and ions move. o Calculate standard emfs (cell potentials), E cell, from standard reduction potentials. Use reduction potentials to predict whether a redox reaction is spontaneous. o o Relate E cell to DG and equilibrium constants. Calculate emf under nonstandard conditions. Identify the components of common batteries. Describe the construction of a lithium-ion battery and explain how it works. Describe the construction of a fuel cell and explain how it generates electrical energy. Explain how corrosion occurs and how it is prevented by cathodic protection. Describe the reactions in electrolytic cells. Relate the amounts of products and reactants in redox reactions to electrical charge. Electrochemistry Electrochemistry is the study of the relationships between electricity and chemical reactions. • It includes the study of both spontaneous and nonspontaneous processes. 1 Redox reactions: assigning oxidation numbers Oxidation numbers help keep track of what species loses electrons and what species gains them. • An element is oxidized when the oxidation number increases • An element is reduced when the oxidation number decreases • an oxidizing agent causes another element to be oxidized • a reducing agent causes another element to be reduced. Assigning oxidation numbers (sect. 4.4) 1. Elemental form, each atom has ox. # = 0. Zn O2 O3 I2 S8 P4 2. Simple ions, = charge on ion. -1 for Cl-, +2 for Mg2+ 3.
  • Introduction to Chemistry

    Introduction to Chemistry

    Introduction to Chemistry Author: Tracy Poulsen Digital Proofer Supported by CK-12 Foundation CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook Introduction to Chem... materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based Authored by Tracy Poulsen collaborative model termed the “FlexBook,” CK-12 intends to pioneer the generation and 8.5" x 11.0" (21.59 x 27.94 cm) distribution of high-quality educational content that will serve both as core text as well as provide Black & White on White paper an adaptive environment for learning. 250 pages ISBN-13: 9781478298601 Copyright © 2010, CK-12 Foundation, www.ck12.org ISBN-10: 147829860X Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made Please carefully review your Digital Proof download for formatting, available to Users in accordance with the Creative Commons Attribution/Non-Commercial/Share grammar, and design issues that may need to be corrected. Alike 3.0 Unported (CC-by-NC-SA) License (http://creativecommons.org/licenses/by-nc- sa/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), We recommend that you review your book three times, with each time focusing on a different aspect. which is incorporated herein by this reference. Specific details can be found at http://about.ck12.org/terms. Check the format, including headers, footers, page 1 numbers, spacing, table of contents, and index. 2 Review any images or graphics and captions if applicable.
  • Battle of the Acids Weak Acids and Bases SCIENTIFIC

    Battle of the Acids Weak Acids and Bases SCIENTIFIC

    Battle of the Acids Weak Acids and Bases SCIENTIFIC Introduction Not all acids are created equal. This demonstration compares the “frothing and foaming” activity of different acids with calcium carbonate and examines their behavior in the presence of their conjugate bases to distinguish strong versus weak acids. The use of a “rainbow acid” universal indicator produces a rainbow spectrum of color changes as the mixtures react. Concepts • Strong acid • Weak acid • Conjugate base • pH Materials (for each demonstration) Acetic acid, CH3COOH, 1 M, 400 mL Water, distilled or deionized Calcium carbonate, CaCO3, 40 g Demonstration tray, large Hydrochloric acid, HCl, 1 M, 400 mL Graduated cylinder, 250-mL “Rainbow acid” universal indicator, 5 mL Hydrometer cylinders, 600-mL, 4 (includes accompanying color chart) Pipet, Beral-type Sodium acetate, NaCH3CO2, 16 g Weighing dishes or small beakers, 6 Sodium chloride, NaCl, 12 g Safety Precautions Hydrochloric acid and acetic acid solutions are toxic and corrosive. Avoid contact with skin and eyes. “Rainbow-acid” universal indicator solution is an alcohol-based solution and is flammable. Avoid contact with flames or other ignition sources. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Please review current Material Safety Data Sheets for additional safety, handling, and disposal information. Preparation To save time in the presentation, pre-measure the amounts of solids needed for the demonstration. Weigh out 12 g of sodium chloride, 16 g of sodium acetate, and 4 × 10-g samples of calcium carbonate in separate, labeled weighing dishes or small beakers. Procedure 1. Obtain 4 large hydrometer cylinders or tall-form beakers and place them on a large demonstration tray.
  • Sulfur Dioxide in Workplace Atmospheres (Bubbler)

    Sulfur Dioxide in Workplace Atmospheres (Bubbler)

    Withdrawn Provided For Historical Reference Only SULFUR DIOXIDE IN WORKPLACE ATMOSPHERES (BUBBLER) ♦ Method Number: ID-104 Matrix: Air OSHA PEL Sulfur Dioxide (Final Rule Limit): 2 ppm (Time Weighted Limit) 5 ppm (Short-Term Exposure Limit) Sulfur Dioxide (Transitional Limit): 5 ppm (Time Weighted Limit) Collection Device: A calibrated personal sampling pump is used to draw a known volume of air through a midget-fritted glass bubbler containing 10 to 15 mL of 0.3 N hydrogen peroxide. Recommended Air Volume: 15 to 60 L Recommended Sampling Rate: 1 L/min Analytical Procedure: Samples are directly analyzed with no sample preparation by ion chromatography as total sulfate. Detection Limit Qualitative: 0.0041 ppm (60-L air volume) Quantitative: 0.010 ppm (60-L air volume) Precision and Accuracy Validation Level: 2.5 to 10.0 ppm (60-L air volume) CVT 0.012 Bias -0.046 Overall Error ±7% Method Classification: Validated Method Chemist: Ted Wilczek, Edward Zimowski Date (Date Revised): 1981 (December, 1989) Commercial manufacturers and products mentioned in this method are for descriptive use only and do not constitute endorsements by USDOL-OSHA. Similar products from other sources can be substituted. Branch of Inorganic Methods Development OSHA Technical Center Salt Lake City, Utah 1 of 9 Note: OSHA no longer uses or supports this method (November 2019). Withdrawn Provided For Historical Reference Only 1. Introduction This method describes the collection and analysis of airborne sulfur dioxide (SO2) using midget-fritted glass bubblers (MFGBs) in the workplace. It is applicable for both short-term (STEL) and time weighted average (TWA) exposure evaluations.
  • Stoichiometry of Chemical Reactions 175

    Stoichiometry of Chemical Reactions 175

    Chapter 4 Stoichiometry of Chemical Reactions 175 Chapter 4 Stoichiometry of Chemical Reactions Figure 4.1 Many modern rocket fuels are solid mixtures of substances combined in carefully measured amounts and ignited to yield a thrust-generating chemical reaction. (credit: modification of work by NASA) Chapter Outline 4.1 Writing and Balancing Chemical Equations 4.2 Classifying Chemical Reactions 4.3 Reaction Stoichiometry 4.4 Reaction Yields 4.5 Quantitative Chemical Analysis Introduction Solid-fuel rockets are a central feature in the world’s space exploration programs, including the new Space Launch System being developed by the National Aeronautics and Space Administration (NASA) to replace the retired Space Shuttle fleet (Figure 4.1). The engines of these rockets rely on carefully prepared solid mixtures of chemicals combined in precisely measured amounts. Igniting the mixture initiates a vigorous chemical reaction that rapidly generates large amounts of gaseous products. These gases are ejected from the rocket engine through its nozzle, providing the thrust needed to propel heavy payloads into space. Both the nature of this chemical reaction and the relationships between the amounts of the substances being consumed and produced by the reaction are critically important considerations that determine the success of the technology. This chapter will describe how to symbolize chemical reactions using chemical equations, how to classify some common chemical reactions by identifying patterns of reactivity, and how to determine the quantitative relations between the amounts of substances involved in chemical reactions—that is, the reaction stoichiometry. 176 Chapter 4 Stoichiometry of Chemical Reactions 4.1 Writing and Balancing Chemical Equations By the end of this section, you will be able to: • Derive chemical equations from narrative descriptions of chemical reactions.
  • Guidelines for the Preservation of Raw Milk by Use of the Lactoperoxidase System

    Guidelines for the Preservation of Raw Milk by Use of the Lactoperoxidase System

    GUIDELINES FOR THE PRESERVATION OF RAW MILK BY USE OF THE LACTOPEROXIDASE SYSTEM CAC/GL 13-1991 INTRODUCTION Milk is an easily perishable raw material. Contaminating bacteria may multiply rapidly and render it unsuitable for processing and/or unfit for human consumption. Bacterial growth can be retarded by refrigeration, thereby slowing down the rate of deterioration. Under certain conditions refrigeration may not be feasible due to economical and/ or technical reasons. Difficulties in applying refrigeration are specially a problem for certain areas in countries setting up or expanding their milk production. In these situations, it would be beneficial to have access to a method, other than refrigeration, for retarding bacterial growth in raw milk during collection and transportation to the dairy processing plant. In 1967 the FAO/WHO Expert Panel on Milk Quality concluded that the use of hydrogen peroxide might be an acceptable alternative in the early stages of development of an organized dairy industry, provided that certain conditions were complied with. However, this method has not achieved any general acceptance as it has several drawbacks, most important of which is the difficulty of controlling its use: it may be misused to disguise milk of basic hygienic quality produced under poor hygienic conditions. The toxicological aspects of the use of relatively high concentrations of hydrogen peroxide in milk have also been questioned. A chemical method for preserving milk would still be of great advantage in certain situations. The search for such a method has therefore continued. Interest has recently been focused on the indigenous antibacterial systems in milk to determine if these could be applied practically to preserve raw milk.
  • 15-1 SECTION 15 ELECTROCHEMISTRY Electrochemistry: the Branch of Chemistry That Covers the Relative Strengths of Oxidants and R

    15-1 SECTION 15 ELECTROCHEMISTRY Electrochemistry: the Branch of Chemistry That Covers the Relative Strengths of Oxidants and R

    15-1 SECTION 15 ELECTROCHEMISTRY Some systems involving redox reactions can be designed so that the reactants (and products) are partially separated from each other, and the reaction leads to an electric current being produced in an external circuit, and which can be used for many useful purposes. Batteries and their many uses are the obvious examples. Electrical energy can also be used to drive non-spontaneous chemical reactions to produce desired products in processes known as electrolysis. This section introduces the language and concepts of these processes collectively known as electrochemistry. Electrochemistry: The branch of chemistry that covers the relative strengths of oxidants and reductants, the production of electric current from chemical reactions, and the use of electricity to produce chemical change. Electrochemical cell: A system made up of two electrodes in contact with an electrolyte. Electrode: A conductor of electricity, commonly a metal or graphite in contact with an electrolyte in an electrochemical cell. Electrolyte: A medium (phase) which conducts electricity by the movement of ions [e.g. a molten salt] or a substance which dissolves in a solvent to give a conducting solution [e.g. aqueous sodium chloride, NaCl or any other soluble ionic compound]. Electrode reaction: A chemical reaction occurring at an electrode involving gain or loss of electrons. It is called a half-reaction. [e.g. Cu2++ 2e– → Cu; Zn → Zn2+ + 2e– ] (See page 12-4.) Redox couple: The two species of a half- reaction involving oxidation or reduction. (See 2+ – page 12-3.) Represented as oxidised species/reduced species [e.g. Cu /Cu; Cl2/Cl ; Fe3+/Fe2+].
  • Chemical Reactions Name C2H4O2 + Nahco3

    Chemical Reactions Name C2H4O2 + Nahco3

    Chemical Reactions Name ________________________ 1. Look at the chemical equation for the reaction between vinegar and baking soda to answer the following questions. C2H4O2 + NaHCO3 → NaC2H3O2 + H2O +CO2 acetic acid + sodium bicarbonate → Sodium acetate + Water + carbon dioxide What are the reactants in this chemical reaction? What are the products in this chemical reaction? C2H4O2 + NaHCO3 → NaC2H3O2 + H2O +CO2 Atom Reactant side Product side Carbon Hydrogen Oxygen Sodium 2. How many of each type of atom appears on each side of the chemical equation? 3. What does the statement “Mass is conserved during a chemical reaction” mean? Activity Question to investigate How can you make just the right amount of foam that rises to the top of the graduated cylinder without overflowing? Materials for each group • Vinegar in a cup • Baking soda in a cup • Detergent solution in a cup • Dropper • Graduated cylinder (50 mL) • Measuring spoons • Plastic overflow container Procedure 1. Decide on how much vinegar and baking soda you will use and write these amounts in the chart on the activity sheet. 2. Use a graduated cylinder to measure the amount of vinegar your group agreed on. 3. Pour the vinegar in a small cup and add 1 drop of detergent. Swirl gently to mix. 4. Add the amount of baking soda your group agreed on to the empty graduated cylinder. 5. Place the graduated cylinder in a plastic overflow container. 6. Pour the vinegar and detergent from the cup into the graduated cylinder. Observe the level of foam in the graduated cylinder 7. Rinse the graduated cylinder over the waste container.
  • Chemical Reactions Chemical Reactions Change Substances Into Other Substances

    Chemical Reactions Chemical Reactions Change Substances Into Other Substances

    Chemical reactions Chemical reactions change substances into other substances. A chemical equation is used to represent a reaction. This has the form: reactants products Word equations use the names of the reactants and products. e.g. hydrogen + oxygen water Balanced symbol equations use the formulae of the reactants and products. e.g. 2 H2 + O2 2 H2O What happens in a chemical reactions: • Chemical bonds in the reactants are broken – this requires energy • The atoms are rearranged to make new substance(s) • New bonds are formed to hold the atoms together in the products Balancing Equations No atoms are lost or gained during a chemical reaction – all the atoms in the reactants are there in the products. This is why equations have to be balanced. This means that mass does not change during a chemical reaction – mass is conserved. We use numbers in front of the chemical formulae so that the rule about all the same atoms being present before and after is true. We never change the formulae themselves - that would make it a different chemical reaction. e.g. H2 + O2 → H2ONOT BALANCED 2H2 + O2 → 2H2O BALANCED State Symbols We use these to show the physical state of the substances in equations: (s) for solid (l) for liquid (g) for gas (aq) for aqueous solution (i.e. dissolved in water) e.g. Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g) “Solid calcium will react when placed in water, producing a solution of calcium hydroxide and bubbles of hydrogen gas” Acids, especially concentrated acids, are corrosive: you need eye protection and gloves.
  • Voltaic Cells

    Voltaic Cells

    Electrochemistry & Redox Voltaic Cells A voltaic electrochemical cell involves two half cells one containing an An oxidation-reduction (redox) reaction involves oxidising agent and the other a reducing agent. the transfer of electrons from the reducing agent These cells are connected with a to the oxidising agent. wire, to allow electron flow and a salbdlt bridge to compl ete th e circuit and maintain electrical neutrality. The PULL or DRIVING FORCE on the electrons is the cell OXIDATION - is the LOSS of electrons Zn(s) Zn2+(aq) + 2e-(aq) potential (Ecell) or the REDUCTION - is the GAIN of electrons Cu2+(aq) + 2e-(aq) Cu(s) electromotive force (emf) of the cell, measured in volts. These represents the redox HALF-EQUATIONS 1 2 Electrochemical Cells Balancing Redox Equations An ox, red cat Anode: oxidation The concept of Oxidation Number is artificial. In simple ions it Voltaic (Galvanic) cells are those Reduction: cathode in which spontaneous chemical is equivalent to the charge on the ion. reactions produce electricity and Oxidation involves an increase in oxidation number supply it to other circuits. Reduction involves a decrease in oxidation number G < 0 As half cells, determine oxidation numbers and balance electrons. Electrolytic cells are those in Combine half cells balancing gain/loss of electrons. which electrical energy causes + - Balance with H O and H or H O and OH . non-spontaneous chemical 2 2 reactions to occur. Check charges balance. G > 0 0 +II Zn(s) Zn2+(aq) + 2e-(aq) +II 0 Cu2+(aq) + 2e-(aq) Cu(s) Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) 3 4 Standard Reduction Potentials Calculating Cell Potential In data tables half cells are written as reductions.