5. The glass electrode used in commercial pH meters gives an electrical response

Question

5. The glass electrode used in commercial pH meters gives an electrical response proportional to the concentration of hydrogen ion. To convert these responses to a pH reading, the electrode must be calibrated against standard solutions of known H+ concentration. Determine the weight in grams of sodium dihydrogen phosphate (NaH2PO4? H2O; FW 138) and disodium hydrogen phosphate (Na2HPO4? H2O; FW 142) needed to prepare 1L of a standard buffer at pH 7.0 with a total phosphate concentration of 0.1 M. pKa of phosphoric acid 6.86.

Explanation / Answer

The amount needed for 1 L of solution = FW (mol/L). ..

For NaH2PO4 H2O: (138 g/mol)(0.042 mol/L) = 5.8 g/L..

For Na2HPO4: (142 g/mol)(0.058 mol/L) = 8.2 g/L...

for full detail please download this pdf. solution is at question 19...

http://www2.fiu.edu/~bch3033/probsolns/solutionsch02.pdf

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