i need guide for D and E 2. You weigh a sample of a monoprotic unknown acid and

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i need guide for D and E
2. You weigh a sample of a monoprotic unknown acid and dissolve it in 50.00 mL of distilled water. Exactly half of this solution is titrated with Sodium Hydroxide to the phenolphthalein end point.
The pH of the other half of the original solution is measured with a pH meter. The "neutralized" solution is added to the "original" solution and the pH of this combined "final" solution is also measured.
The following are the measured values:
Mass of unknown acid 1.8105 g
Volume of NaOH used in titration 13.80 mL
Concentration of the NaOH used 0.2213 M
pH of the original acid solution 2.13
pH of the final acid solution 3.24

CALCULATE the following
(a) Molecular Weight of Acid used in titration ____________296.4_______

(b) Molarity of UNKNOWN Acid solution from titration ____________.1222_______

(c) Ka of UNKNOWN Acid _____________.000575______

(d) Concentration of undissociated Acid from pH measurements ___________________

(e) Total concentration of UNKNOWN acid from pH measurements ___________________

Explanation / Answer

The dissociation of the monoprotic acid is as follows:

HA <===> H+(aq) + A-(aq)

(c-x)              x            x

Initial moles of acid used = 1.8105/296.4 = 0.0061

pH of the original acid solution= 2.13 = -log [H+ (from acid dissociated)]

So, total concentration of acid dissociated = [H+(from acid dissociated)] = 0.0074

Total volume of the original solution= 50.0 ml= 0.05 L

Initial moles of acid used = 0.0061

So, original concentration of acid used/dissolved = moles/Vol (L) = 0.0061/0.05 = 0.122 M

Thus,

(d) concentration of undissociated acid from pH measurements = 0.122-0.0074 = 0.11476 M

(e) Total concentration of unknown acid from pH measurements= 0.122 M

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