Chemistry 2000, Section A
Spring 1996 Final Examination

You have three hours to complete this exam. You may not leave the examination hall in the first hour. The aggregate value of all questions on this exam is 100. The value of each question is indicated in the margin. Your answers must be recorded in the exam booklets provided. Please note the useful information on the back page.

1. Short answer questions:
   1. If a reaction has a rate-determining step what is the order of the reaction with respect to B?
   2. A living cell placed in distilled water bursts. Why?
   3. Which is higher: The vapour pressure of pure water at C or the vapour pressure of a sodium chloride solution at C?
   4. Give three different ways you can use to decide whether or not a reaction is spontaneous.
   5. Does the equilibrium constant of an exothermic process increase or decrease with temperature?
   6. What are the three conditions for the production of electricity by a chemical reaction?
2. Short problems:
   1. For the reaction , and the initial concentration of A is 1mol/L. What is the equilibrium concentration of B?
   2. What is the pH of a 0.02mol/L sodium hydroxide solution at C?
   3. A solution of oxalic acid (H C O ) is mixed with a hydrogen peroxide (H O ) solution. A redox reaction occurs and carbon dioxide bubbles out. Balance the reaction.
   4. What is the entropy change in the reaction ?
   5. For the reaction , V. What is ?
3. Suppose that a chemist measures the rate of disappearance of a reactant A as a function of concentration for the reaction :

   

   1. What is the experimental rate equation for [A]?
   2. Calculate the rate constant.
4. 2.5g of solid sodium acetate (molar mass 82.03g/mol) is dissolved in 100mL of a 0.4mol/L aqueous HCl solution in an insulated container at constant pressure.
   1. What is the pH of the solution at equilibrium?
   2. If the HCl solution starts at C, what is the final temperature?
5. Lead (II) azide (Pb(N ) , molar mass 291.2g/mol) is a highly explosive substance. The chemical reaction which occurs when lead (II) azide explodes is unknown. However,

   

   is a reasonable guess. The reaction generates the products in stoichiometric quantities.

   1. A 200g sample of lead (II) azide explodes. Its initial temperature is C. Suppose that all of the heat liberated by the reaction is held in the products. (This is a reasonable approximation when a chemical reaction occurs quickly. The heat just doesn't have time to get away.) What is the final temperature of the products?
   2. What is the volume of gas produced at 1atm? Express your answer in litres.
6. 1. Calculate the vapour pressure of pure pentane at C.
   2. If 10g of dodecane (C H , molar mass 282.552g/mol) is dissolved in 30g of pentane (molar mass 72.150g/mol), what is the vapour pressure of the solution? Note that dodecane has a much lower vapour pressure than pentane.
7. The half-reactions in the lead-acid battery are

   

   1. What is the overall reaction when the battery is producing electricity?
   2. Calculate the voltage produced by this battery when the sulphuric acid concentration is 2mol/L at C.
8. The solubility product of AgBr is in water at C. What is the solubility of silver bromide in boiling water? Neglect the boiling point elevation due to the dissolved silver bromide.
9. At C, the equilibrium constant for the reaction

   

   is 0.534. If 0.2atm of H and 0.8atm of CO are mixed in a rigid container, what are the equilibrium pressures of the four gases?

10. The protonated aniline cation (C H NH ) is a monoprotic acid with a pKa of 4.6. This acid is normally obtained by reacting aniline (C H NH ) with a strong acid. You are given 1L of a 0.2mol/L aniline solution and a 1mol/L HCl solution. How much of the HCl solution should you add to the aniline solution to make a pH 5 buffer?

Useful data

Formulas