May 24, 2015

Homework Help: Chemistry

Posted by Stuck on Saturday, May 15, 2010 at 12:16am.

"An aqueous sodium borate solution is titrated to the second endpoint with 0.225 mol/l nitric acid in the presence of a suitable indicator. If an average of 12.6mL of titrant are required to reach the second endpoint for a 25.0 mL sample, what is the base concentration?"

My calculations:

nHNO3: (0.225 mol/l)(12.6 mL)/1000
= 2.835 x 10^-3 mol

nNa3BO3: (2.835 x 10^-3 mol)(1/3)
= 9.45 x 10^-4 mol

[Na3BO3]: (9.45 x 10^-4 mol)/(25 mL)(1000)
= 0.0378 mol/L

Is this correct? Because the answer given is different (0.0567 mol/L).

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