Make sure you show all your calculations in the space provided after each question. Full credits will not be given if only the final answer is written.
1. a. (i) What is a buffer?
(ii) Give two examples of a buffer system.
(iii) Why is it that HCl/NaCl is not a buffer.
b. Consider the buffer system of nitrous acid, HNO2, and its salt, NaNO2.
HNO2(aq) + H2O(l) ==== H3O+(aq) + NO2-(aq)
(i) The purpose of this buffer system is to: (A) maintain [HNO2] (B) maintain [NO2-] (C) maintain pH
(ii) The weak acid is added to: (A) provide the conjugate base (B) neutralize added OH- (C) provide the conjugate acid
(iii) If H3O+ is added, it is neutralized by: (A) the salt (B) H2O (C) OH-
(iv) When OH- is added, the equilibrium shifts in the direction of the: (A) the reactants (B) products (C) does not change
c. A 10.0-mL of vinegar which is an aqueous solution of acetic acid, HC2H3O2, requires 16.5 mL of a 0.500 M NaOH solution to reach the endpoint in a titration. What is the molarity of the acetic acid solution?
HC2H3O2 (aq) + NaOH (aq) ————- NaC2H3O2(aq) + H2O(l)
2. Consider the compound butane,
a. Draw the condensed structural formula of butane
b. Write the balanced chemical equation for the complete combustion of butane
c. How many grams of O2 are needed to react with 12.0 L of butane gas at STP?
(At STP, 1 mole of any gas occupies 22.4 L)
d. How many grams of CO2 would be produced from the reaction in question c above?
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