CK-12 Chemistry Concepts - Intermediate Answer Key

Transcription

1 CK-12 Chemistry Concepts - Intermediate Answer Key Chapter 22: Oxidation-Reduction Reactions 22.1 Oxygen in Reactions Answer the questions at the following link: are found here: 1. Give a definition of oxidation in terms of oxygen. 2. Give a definition of reduction in terms of oxygen. 3. Characterize the following reaction in terms of the definitions of oxidation and reduction: 1. Oxidation a gain of oxygen. 2. Reduction a loss of oxygen. 3. carbon oxidized lost H, added O. oxygen reduced added H Redox Reactions and Ionic Compounds 1

2 In each reaction below, identify the material that is oxidized and the material that is reduced: 1. 2 AgCl(s)+H 2 (g) 2 H + (aq)+2 Ag(s)+2 Cl 2. H 2 +F 2 2 HF 3. Fe+CuSO 4 FeSO 4 +Cu 1. AgCl is reduced and H is oxidized. 2. H is oxidized and F is reduced. 3. Fe is oxidized and Cu is reduced. 1. In the Zn + S reaction, why do we say that the Zn was oxidized? 2. In that reaction, why do we say that S was reduced? 3. In a reaction, we see the following half-reaction: K 0 K +. Was K oxidized or reduced? 1. It lost electrons. 2. It gained electrons. 3. It was oxidized Oxidizing and Reducing Reactions Do problem one at the link below: t%20redox.pdf are found on the website. 2

3 1. Define oxidizing agent. 2. Define reducing agent. 3. How does identifying the common ions help in the solution of a redox problem? 1. The substance that causes oxidation by accepting electrons. 2. The substance that causes reduction by losing electrons. 3. Identifying common ions is useful in knowing the charges of the components of the reaction Molecular Redox Reactions In each of the following reactions, state whether C is oxidized or reduced: 1. CH 3 CH 2 CH 2 CH 3 CH 3 CH=CHCH CH 3 CH=CH 2 CH 3 CH 2 CH 3. In the following reaction, state whether O is oxidized or reduced: 3. CH 3 CH=O CH 3 CH 2 OH. 1. Oxidized, lost H. 2. Reduced, added H. 3. Reduced, added H. 1. Where are the electrons in the hydrogen and oxygen molecules covalent bonds? 2. How does oxygen gain electrons in the water molecule? 3. How does hydrogen lose electrons in the water molecule? 3

4 1. In each case they are equidistant between the two atoms of the molecule. 2. Oxygen is more electronegative than hydrogen and will attract the covalent bond electrons closer to itself than to hydrogen. 3. Hydrogen is less electronegative than oxygen and is less likely to attract the electrons to itself Corrosion Read the material at the link below and define the following terms: 1. atmospheric. 2. galvanic. 3. high temperature. 1. Corrosion cause by materials in the atmosphere such as air pollution, salt spray, and moisture. 2. Two different metals in contact with each other and with an electrolyte. 3. Temperature high enough to speed up reaction with oxygen. 1. What is corrosion? 2. How does aluminum avoid complete corrosion? 3. What is the purpose of cathodic protection? 1. Redox processes that cause metals to deteriorate. 2. It forms a protective coating of aluminum oxide on its surface. 3. Have a more active metal available for reaction to prevent the steel ship from rusting Assigning Oxidation Numbers 4

5 Work the problems at the link below: are given on the web site. 1. What is the oxidation number for the element zinc? 2. Nitrogen can exist in several oxide forms. What is the oxidation number of N in NO? in N 2 O? in NO 2? 3. What is the oxidation number of H in HCl? in NaH? 1. Zero since it is an element , +2, , Changes in Oxidation Number in Redox Reactions Complete problems at the link below: are given on the web site. 5

6 1. In the example reaction above, list the ways the reduction of ferric oxide fits the definitions of oxidation and reduction. 2. In the reaction below, what is oxidized and what is reduced? Cr2O3(s)+2Al(s) 2Cr(s)+Al2O3(s) 3. List the ways that the conversion of aluminum in the reaction above fits the definitions in the table. 1. Ferric oxide is reduced as the oxidation number of iron(iii) decreases from +3 to 0. Oxygen is lost, which also indicated reduction. 2. Aluminum is oxidized and chromium(iii) oxide is reduced. 3. Oxygen is added to the aluminum, and its oxidation number is increased Identifying Reaction Types Indicate which of the following reactions are redox reactions and which are not: You do not need to write explanations or balance the equations. 1. Yes. 2. Yes. 3. No. 4. No. 5. Yes. 1. Why is the Zn + HCl reaction a redox reaction? 2. Why is the sodium sulfate + barium nitrate reaction not a redox reaction? 3. Dos the transfer of H + affect oxidation numbers? 1. Zn is oxidized and Cl is reduced. 6

7 2. There are no changes in any oxidation numbers. 3. No Balancing Redox Reactions: Oxidation Number Change Method Balance the equations at the link below: are given on the website. 1. Why is it important to assign oxidation numbers to all the atoms in the equation? 2. What are we really balancing using this method? 3. What do we adjust to make electrons gained equal electrons lost? 1. So the equation can be correctly balanced. 2. The electrons that are lost and gained. 3. Coefficients Balancing Redox Reactions: Half-Reaction Method Do all half-reaction equation balancing problems at the link below: are given at the web site. 7

8 1. Why do you need the unbalanced ionic equation? 2. What does balancing each half-reaction separately tell you? 3. How do you balance hydrogens in an acidic medium? 1. Because the reduction and oxidation reactions need to be balanced separately before being added back together. 2. Allows you to balance out the atoms and the charges of the reduction and oxidation reactions separately. 3. By adding hydrogen ions to the side of the equation which needs them Half-Reaction Method in Basic Solution Balance the equations at the link below: are provided on the web site. 1. How many OH - should be added to each side? 2. When does the oxidation-number approach work best? 3. When does the half-reaction method work best? 1. An equal number, which combines with the H + present on one side of the equation to form water. 2. If the oxidized and reduced species appear only once on each side of the equation, and there are no acids or bases present. 8

9 3. For reactions of ions in aqueous solutions. 9