Chem 104

Spring '03 name______________________

Quiz #3

1. What is:

(a) The [OH-] in a solution at pH = 4? 10^-10 M

(b) What is the conjugate base of nitric acid? Nitrate, NO3-

(c) What is the strength of the conjugate base of perchloric acid? Extremely weak

(c) pKa1 for citric acid, is 3.13. What is the Kb for citrate?

PKb = 14- pKa = 10.87,

Kb = 10^ - 10.87 = 1.35 x 10^-11

2. 50.0 mL of perchloric acid having a concentration of 0.100 M is mixed with an aqueous solution of 10 mL sodium hydroxide having a concentration of 1.0 M and then the solution is diluted to a final volume of 1.00 L.

(a) What are the pH and pOH of the final solution?

Reaction; HClO4 + NaOH = ClO4- + Na+ + H2O, strong acid, strong base

# moles HClO4 = 0.050 L x 0.100 M = 0.005 moles (limiting reagent)

# moles NaOH = 0.010 L x 1.0 M = 0.100 moles

after reaction, # moles HClO4 = 0, all reacted

# moles NaOH = ( 0.100 – 0.005) moles = 0.005 moles.

[OH] = 0.005 mol/ 1.0 L = 0.005 M

pOH = 2.30

pH = 12.70