Question 8 of 9 Map Sapling Learning macmillan learning Arsenic acid is a tiproc

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Question 8 of 9 Map Sapling Learning macmillan learning Arsenic acid is a tiproc id with the following pK, values pKa 2.240 pK2 6960 pK-1.500 You wish to prepare 1.000 L of a 0.0300 M arsenate buffer at pH 6.620. To do this, you choose to mix the two salt forms involved in the second ionization, NaH2AsO4 and Na2HAsO4, in a 1.000 L volumetric flask and add water to the mark. What mass of each salt will you add to the mixture? Number mass NaH2Aso,L gmass Na,HAsO, ..Joading modules... Previous Give Up & View Solution Check Answer ) Next Exit Hint

Explanation / Answer

pH = pka +log(Na2HAsO4/NaH2Aso4)

No of mol of buffer = 1*0.03 = 0.03 mol

buffer = Na2HAsO4 + NaH2Aso4

0.03 =   x + 0.03-x

pka2 = 6.96, pH = 6.62

6.62 = 6.96 +log(x/(0.03-x))

x = 0.00941

No of mol of Na2HAsO4 = x = 0.00941 mol

amount of Na2HAsO4 = 0.00941*186 = 1.75 g

No of mol of NaH2AsO4 = 0.03- 0.00941 = 0.0206 mol

amount of NaH2AsO4 = 0.0206*164 = 3.38 g

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