CHM 2045C Module Eight Sample Exam Answers

Module Eight: Solutions/Oxidation & Reduction (Chapter 5)

Part I: Solution Discussion Questions 5 points

Answer any two of the following:

(1) Define oxidation and reduction in terms of electron transfer.

Oxidation-the removal or loss of electrons

Reduction-The addition or gain of electrons

(2) In an oxidation/reduction equation, what is the oxidizing agent?

The substance that is reduced is by definition the substance that oxidizes the other. It is called the oxidizing agent or the oxidizer. So you can say the oxidizing agent or oxidizer is reduced

What is the reducing agent?

The substance that is oxidized must reduce the other substance. It is called the reducing agent or the reducer. So you can say the reducing agent or reducer is oxidized.

(3) How can you recognize whether a reaction is a redox reaction or not?

You can tell whether a reaction involves oxidation and reduction by assessing the oxidation number of each element and noting whether any of these numbers change in the course of the reaction.

(4) Name three types of reactions which are NOT oxidation reduction and give at least one example:

Precipitation Reaction-formation of an insoluble compound:

Pb(NO₃)₂ (aq) + 2 KCl (aq) à PbCl₂ (s) + KNO₃ (aq)

Acid-Base; Neutralization Reaction: Reaction of an acid and base forms a salt and water as products: HCl (aq) + NaOH (aq) à NaCl (aq) + H₂O (L)

Gas-Forming Reactions: Evolution of a water insoluble gas such as CO₂ as a product

Na₂CO₃ (aq) + 2 HNO₃ (aq) à 2 NaNO₃ (aq) + H₂O (L) + CO₂ (g)

(5) What is the equivalence point in a titration of an acid and a base? Is there a difference between the equivalence point and the end point of the titration when using an acid/base indicator to determine the end point?

The equivalence point in an acid/base titration is the point at which the acid or base being added produces enough ions so that the amount of OH^1- ions equals the H₃O ¹⁺ ions. When using an acid/base indicator, a dye that changes color when the pH of the reaction solution changes past the equivalence point, the color change point is the end point. Adding one drop at end point changes the pH usually at least two pH units which includes the equivalence point. The end points is a range of pH value, while the equivalence points is an exact points of 7.00 on the pH scale..