pH glass electrode analysis HELP.

[lam58]

Hi, i'm stuck on part b) of the question below:[/size]

Q: In order to perform pH determinations with a glass electrode, the cell potential was measured for threestandard solutions with the following pH values at 25 Celsius: 2.04, 7.05, and 9.20. The cell voltage readout(in mV) for each of the above solutions was 238.0, -37.5 and, -164.5, respectively. Calculate: (a) thesensitivity of the pH sensor; (b) the pH of an unknown sample yielding a cell voltage of 20.5 mV; © thepH deviation from the actual value if the sample temperature is 35 Celsius.

My Ans is in the image below, click to enlarge.

Edited December 29, 2015 by lam58