A) what is the Ka value? B) what was the initial concentration of the acid? C) w

Question

A) what is the Ka value?
B) what was the initial concentration of the acid?
C) what is the volume of .500M NaOH at equivalent point?
D) what is the molecular mass of the acid?
E) calculate the moles of the monoprotic acid that was neutralized in the reaction? - itraed 0.750 gof a solid of unknown mosopeotic acid that O mil. of distilled water, the initial pll value was 2.92. They found thas 489 when 12.5 ml of Nall hd been added The concentration of the sodium 24. The Quantitative Analysis class was dissolved in $0.0 mil of pk-4 hydroxide was 0 500 M a) What is the K, value? Solution Solution What is the volume of 0500M NaOH a·equivalent point? Solution: c) d) Cakculate the moles of the monopeotsic acid that was neutralized in the reaction? Solution e) What is the molecularformula mass of the acid

Explanation / Answer

1) We know that for buffers pH = pKa + log [salt] / [acid]

pH = pKa -4.89

pH = 2.92

so pKa = 7.81

pKa = -log Ka

so Ka = antilog of -pKa

Ka = 1.55 X 10^-8

2) let acid dissociates as

HA--> H+ + A-

Ka = [H+] [A-] / [HA] = x^2 / (a-x)

we can ignore x with respect to a

[H+] = [A-] = antilog of -pH = 0.0012

so [HA] = 0.0012 X 0.0012 / 1.55 X 10^-8

[HA] = 0.929 M

3) moles of acid = concentration X volume

4) concentration of acid = mass of acid / molecular weight of acid X volume of solution

Molecular weight of acid = mass of acid / concentration of acid X volume of solution

5) Moles of NaOH used for neutralization = moles of acid neutralized = volume of base x concentraiton of base

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