Arsenic acid is a triprotic acid with the following pka...

Arsenic acid is a triprotic acid with the following pKa values: pKa1 = 2.240; pKa2 = 6.960; pKa3 = 11.500 You wish to prepare 1.000 L of a 0.0200 M arsenate buffer at pH 6.240. 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?

Transcript

00:01 Students let me explain your question here so here arsenic acid so the acid it is nothing but triprotic acid acid is triprotic acid so triprotachate which contains of three protons these three protons they are dissociate protons dissociable protons so whenever we see the of arsenic acid then we'll get understand water protons so these are the three discuscible protons so this is the arsenic acid okay it consisting of dry protons three protons so here the pca 1 of 2 .240 and pka 2 that is given as 6 .960 and pca 3 is 11 .50.

00:57 So here we have to prepare one liter of 0 .02 molar arsenate buffer.

01:05 Orsonate buffer.

01:07 So at ph, that is ph, it is given as 6 .240.

01:13 So here two salts forms.

01:16 We have to, so we have to mix two salts.

01:20 Okay.

01:22 In the second ionization, what are two salts? n -a -h -2 so two salts form involved in secal identification okay so here n -a -h -2 aso -4 and n -a -2 -h -a -s -o -4 so these two we have to take in one liter volumetric flash so and we have to add water up to the mark so what mass of each salt term so these two salts what mass of each salt we have to add so mass of each salt we have to find out okay so here we know that ph is equal to pk a plus logarithm of n a 2 h a s o4 concentration divided by in a h2 as o four concentration simply we have to substitute the value 6 .24 is equal to 6 .960 plus logarithm of n .a2 h.

02:27 Aso4 divided by n .a .h2 .a .o .4.

02:32 Okay.

02:33 So here whenever we see logarithm of n .a .2 .h .2 aso4 is equal to, so 0 .24 minus 6 .960.

02:49 That is equal to minus 0 .72 .7...

Question

Please give Ace some feedback