[amandagrant07]

Hi
have some very tricky questions to test your brains!! (well they are tricky for me)

a 0.210g sample of a acid (molar mass = 92g/mol) is titrated with 30.5 mL of 0.108M NaOH to a phenolptalein endpoint. What is the formula of the acid??
the answer is H3A but i have no clue where to even start. Can you help??


the next is
you have two solutions of 0.200M HNO2 and 0.2M KNO2 (ka for HNO2 = 4.00*10-4). a buffer of pH 3 is needed. what volumes of HNO2 and KNO2 are required to make 1 litre of buffered solution?

ThANKs in advance for your help

[Borek]

1. How many moles of acid were in the sample? How many were titrated?

2. Have you ever heard about Henderson-Haselbalch equation?