Homework Help: CHEM Buffers

1. Sep 26, 2010

_Bd_

1. The problem statement, all variables and given/known data

You are titrating 30.0 mL of .3 M CH3NH2 with .15 M HNO3 Kb = 4.4 x 10^-4. Calculate
pH:
-initially
-after 10.0 mL of acid has been added
at the half equivalence point
at the equivalence point
when 70 mL of acid has been added.

2. Relevant equations

not sure. . .

3. The attempt at a solution

I was thinking that since Kb is given I can get the pOH using the fact that
[OH] = $$\sqrt{K_b x Molarity}$$ <- im not sure if this is correct tho.

then do an ICE table for the reaction. . . Im not sure about the reaction tho. . .

HNO3 + CH3NH2 >> CH3NH3+ + NO3- . . .is that it?
the first ICE table should be a limiting reagent problem?

knowing the moles of both after 10 mL yields:

HNO3 + CH3NH2 >> CH3NH3+ + NO3-

.0015 | .009 ........| 0.............|0 <<<<<<<<<<Initial
-.0015 |-.0015 .......| +.0015 .....| +.0015 <<<<<<<<Consumed
0 ...|.0075 ..............| .0015 ......| .0015 <<<<<<< Final

so I can get K at this point right? (K = products/reactants) but thats Ka or Kb?

2. Sep 27, 2010