Question

12. Using the Henderson-Hasselbalch equation: [Α] pH = pka + log Calculate what relative amounts of sodium dihydrogen phosphate and sodium monohydrogen phosphate are required to make a buffer solution with pH = 7.9.

please show all work

Answer 1

The relative amount of sodium monohydrogen phosphate to sodium dihydrogen phosphate will be about 5.01.

Solution Buffen :- A leuffer solution may be defined as the aqueous solution of a mly ture of a weak acid its conjugate base on a mean lease & its conjugate acid. It is used for making constant the pH. when a strong acid is added/base to the solution, its pH changes ley a very small amount. Dihy doeogen phosphate — monohydrogen phosphate + ka = 6-3x10-8 Nath,POq+ 0 Nattpoa + H₂O Here, the ginen pH to be made 7.9 volume assumed be 1/1000 mL

Now, Acconding to Henderson - Hasselbalch equation, - pH pkat log (A/ Ka = 6.3x10-8 pka log (6.3x10-3) pka = 7.2 se, from this prstolem, * Ema H, POZ] > loq (NaH POM] 0.7 [MaH₂POq 7.9-7.2 + log [Na HPOK] => [na Hpon], 100% [Naty poj?! [na HP01]. 5.01 [Ma H₂PO4] to [NaH₂ pag] in the medium Aus. The ratio of [Natpay should be apponese 5.01.