File Edit View Window Help Week 6 Homework.pdf Wek Prc2s.. dr2- Home Tools funda

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File Edit View Window Help Week 6 Homework.pdf Wek Prc2s.. dr2- Home Tools funda... Finite... drill2-s... 82.1% Week 6 Assignment A 500 mL buffer is usually prepared with 46 mM carbonic acid and 58 mM sodium bicarbonate. Unfortunately you have run out of these reagents; on hand you have the following: solid citric acid, disodium maleate (salt of maleic acid), benzylamine and hydrochloric acid. Which reagents), and how much of each, would you need to use to produce a 500 mL buffer with the same formal concentration and pH as the carbonic acid buffer? Chemical Concentration or M.W 192.124 g/mol 2.6 M 1.4 M 3 M NIAl Mass or Volume Needed Citric Acid Disodium Maleate Benzylamine Hydrochloric Acid Water 8.50 x 11.00 in Microsoft Wor

Explanation / Answer

To prepare a buffer

original carbonic acid buffer pH

[H2CO3] = 46 mM

[NaHCO3] = 58 mM

pKa = 6.35

Using Hendersen-Hasselbalck equation,

pH = pKa + log(base/acid)

      = 6.35 + log(58/46) = 6.45

Total moles of buffer = ((58 + 46)mM/1000) x 0.5 L = 0.052 mol

Let us begin by benzylamine and add x moles HCl to it

pKa = 9.34

6.45 = 9.34 + log(PhNH2/PhNH3+)

0.0013(PhNH3+) = (PhNH2)

or,

(PhNH2) + (PhNH3+) = 0.052 mol

0.0013(PhNH3+) + (PhNH3+) = 0.052

(PhNH3+) = 0.052/1.0013 = 0.0519 mol

Volume HCl = 0.0519 mol/3 M = 0.0173 L = 17.3 ml

and,

(PhNH2) = 0.052 - 0.0519 = 0.0001 mol

volume PhNH2 (benzylamine) = 0.0001 mol/1.4 M = 7 x 10^-5 L = 0.07 ml

So we would take,

Volume HCl = 17.3 ml

and,

volume PhNH2 (benzylamine) = 0.07 ml

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