How to make a buffer solution with a pH = 10? Insane problem !!!?

Question

pH meter is calibrated using three pH buffers that are equal to 4.00, 7.00 and 10.00. Dr. needs a buffer with the pH = 10. To make a buffer , he gives the following three solutions and three containers of salt:

2L of 2.25 M dimethylamine (CH3)2NH

2L of 4.79M hypobromous acid

3L of 3.41 M chloroacetic acid, CH2ClCOOH

1 kg of dimethyl ammonium chloride (CH3)2NH2Cl

1kg of strontium hypobromite

2kg of sodium chloroacetate, NaCH2ClCOO

Describing in detail what is the best method to make 100.00 mL of a pH=10.00 buffer solution? You may assume that ading those salts to a solution will not increase the volume of the solution.

Holly cow where to start ??????? Please help ! this is insane !!

Answer 1

hypobromous acid hasx an ideal buffer pH = its pKa of 8.6

chloroacetic acid has an ideal buffer pH = its pKa of 2.85

dimethylamine (CH3)2NH is your best choice, it is a base with a Kb = 5.4e-4 . & its ideal buffer pOH = PKb of 3.3, whose pH = 10.7

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a pH = 10,  has a pOH of 4, which has [OH-] = 1e-4

(CH3)2NH  -->  (CH3)2NH2+  &  OH-

2.25 Molar -->     ( x molar)  &  (1e-4 molar)

Kb = [(CH3)2NH2+]  [OH-] / [(CH3)2NH ]

5.4e-4 = [(CH3)2NH2+]  [1e-4] / [2.25 ]

[(CH3)2NH2+]  = 2.4 molar  (CH3)2NH2Cl

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0.100 Litre of buffer @ 2.4 mol/litre  (CH3)2NH2Cl = has 0.24 moles of dimethyl ammonium chloride

0.24 moles of  (CH3)2NH2Cl @ 81.54 g/mol = 19.57 g dimethyl ammonium chloride

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your answer : take 100 ml of 2.25 M dimethylamine (CH3)2NH , dissolve into it 19.6 grams of dimethyl ammonium chloride