Verified Answer :

The solution would be like this
for this specific problem:

moles NH3 = 0.0750 L x
0.200 M=0.015 

moles
HNO3 = 0.0130 L x 0.500 M=0.0065 


NH3 + H+
= NH4+ 

moles NH3
= 0.015 - 0.0065=0.0085 

moles
NH4+ = 0.0065 

pKb =
4.74 

pOH =
4.74 + log 0.0065/0.0085=4.62 


pH = 9.38

So the pH after the
addition of 13.0 mL of HNO_3 is 9.38.

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