Question

1. Valeric acid is a monoprotic acid with a K_{a} value
of 1.44 x 10^{-5}. A student prepared 100.0 mL of a 0.200 M
solution of valeric acid. What is the pH of the valeric acid
solution?

Answer #1

Lets write the acid as HA

Lets write the dissociation equation of HA

HA -----> H+ + A-

0.2 0 0

0.2-x x x

Ka = [H+][A-]/[HA]

Ka = x*x/(c-x)

Assuming small x approximation, that is lets assume that x can be ignored as compared to c

So, above expression becomes

Ka = x*x/(c)

so, x = sqrt (Ka*c)

x = sqrt ((1.44*10^-5)*0.2) = 1.697*10^-3

since c is much greater than x, our assumption is correct

so, x = 1.697*10^-3 M

So, [H+] = x = 1.697*10^-3 M

we have below equation to be used:

pH = -log [H+]

= -log (1.697*10^-3)

= 2.77

Answer: 2.77

1.) If the Ka of a monoprotic
weak acid is 4.5 x 10^-6, what is the pH of a 0.30M solution of
this acid?
2.) The Ka of a monoprotic weak
acid is 7.93 x 10^-3. What is the percent ionization of a 0.170 M
solution of this acid?
3.) Enolugh of a monoprotic acid
is dissolved in water to produce a 0.0141 M solution. The pH of the
resulting solution is 2.50. Calculate the Ka for the
acid.

Citric acid is a triprotic acidwith Ka values of 7.4 x 10-4, 1.7
x 10-5, and 4.0 x 10-7 for the first, second, and third ionization
constants, respectively. A 0.500 M solution of a monoprotic acid
with a Ka value of 7.4 x 10-4 has a pH = 1.72. What is the pH of a
0.500 M citric acid solution?

The Ka of a monoprotic weak acid is 2.29 × 10-3. What is the
percent ionization of a 0.129 M solution of this acid? I got 104.8%
which I know is impossible.
The Ka value for acetic acid, CH3COOH(aq), is 1.8× 10–5.
Calculate the pH of a 2.40 M acetic acid solution.
I also got these incorrect, but am not sure why and would like
to understand. Please help me understand these before my upcoming
test! Thanks! Calculate the pH...

a. Find the pH of a 0.100 M solution of a weak
monoprotic acid having Ka= 1.1×10−5.
b.Find the percent dissociation of this solution.
c. Find the pH of a 0.100 M solution of a weak
monoprotic acid having Ka= 1.8×10−3
d. Find the percent
dissociation of this solution.
e.Find the
pH of a 0.100 M solution of a weak monoprotic
acid having Ka= 0.16.
f.Find the percent dissociation of this solution.

If the Ka of a monoprotic weak acid is 7.5 × 10-6, what is the
pH of a 0.12 M solution of this acid?

If the Ka of a monoprotic weak acid is 3.3 × 10-6, what is the
pH of a 0.30 M solution of this acid?

If the Ka of a monoprotic weak acid is 5.7 × 10-6, what is the
pH of a 0.14 M solution of this acid?

If the Ka of a monoprotic weak acid is 1.6 × 10-6, what is the
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If the Ka of a monoprotic weak acid is 4.7 × 10-6, what is the
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If the Ka of a monoprotic weak acid is 4.7 × 10-6, what is the
pH of a 0.50 M solution of this acid?

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