Biochemistry, Please help with 1 and 2!!! L. You need to prepare a buffer for bi

Question

Biochemistry, Please help with 1 and 2!!!

L. You need to prepare a buffer for biochemistry lab. The required solution is 0.5 M sodium phosphate, pH 7.0. Use the Henderson-Hasselbalch equation to calculate the number of moles and grams of monobasic sodium phosphate (NaH2PO,) and dibasic sodium phosphate (Na2HPO4) necessary to make 1 liter of the solution. 2 Design a "shortcut" method for preparing the phosphate buffer in Study Problem 1. Hint: You need only NaH2PO4, a solution of NaOH, and a pH meter.

Explanation / Answer

1) We can prepare buffer solution by using a weak acid and its salt of strong base:

so here weak acid is: NaH2PO4 and its salt is Na2HPO4

Hendersen Hasselbalch equaiton for buffer is

pH - pKa + log [salt] / [acid]

pKa = 7.2

7 = 7.2 + log [salt] / 0.5

-0.2 = log [salt] / 0.5

taking antilog

0.631 = [salt] / 0.5

[salt] = 0.315

so concentration = 0.315 M

Volume of solution = 1L

So moles of dibasic sodium phosphate = moalrity X volume= 0.315 X 1 = 0.315 moles

gram of dibasic sodium phosphate = moles X molecular weight = 0.315 X 142 = 44.73 grams

2) we can preapre the buffer by adding NaOH to sodium phophate

pH = 7 = 7.2 + log [salt] / [acid]

so the volume of solution = 1L

NaOH + NaH2PO4 --> Na2HPO4

So the amount of added sodium hydroxide will react with monosodium phosphate to give equal mole of disodium phophate.

concentration ratio of salt / acid = 0.315

[salt] = 0.315 [acid]

so take moles of sodium hdyroxide 0.315 times of acid that will be left in acid

so take 0.63 moles of acid and add 0.315 moles of naOH to it.

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