Question

Citric acid, C_{3}H_{5}O(COOH)_{3},
which is present in citrus fruits, is a triprotic acid. Calculate
the concentration of the citrate,
C3H5O(COO)_{3}^{3-} , of a 0.040M solution of
citric acid. Ka,1 = 7.4 x10^{-4}, Ka,2 = 1.7 x
10^{-5}, Ka,3 = 4.0x 10^{-7}

a. 5.08 x10^{-3} M

b. 1.7x10^{-5} M

c. 2.29

d. 1.33 x 10^{-9} M

e. 8.87

Answer #1

Is our assumption valid? 1.7x10-5 dissociated/ 5.08x10-3 initial =
0.33% dissociation = OK!! What if we did not assume? Would the H+
from the second dissociation be enough to change the pH? We can
approximate by using our x value to compare 5.08x10-3 with
(5.08x10-3 + x) 5.08x10-3 + 1.7x10-5 = 0.005737, which produces a
pH of 2.24, so the second dissociation does not significantly
change p.

This equilibrium determines how much citrate ion is in solution,
but its initial concentrations are determined by the previous two
dissociations

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?

What is the pH of a 0.350 M solution of lithium citrate? (Ka
Citric Acid = 7.4 x 10-4)

Calculate the pH of a buffer solution made from 0.10 M
citric acid and 0.25 M citrate, given an acid dissociation constant
for citric acid equal to 1.8 x 10^-5.

Phosphoric acid is a triprotic acid, and the Ka values are given
below. Calculate pH, pOH, [H3PO4], [H2PO4 2-], [HPO4 -], and [PO4
3-] at equilibrium for a 5.00 M phosphoric acid solution.
Ka1 = 7.5 x 10^-3
Ka2 = 6.2 x 10^-8
Ka3 = 4.2 x 10^-13

a) In 2-3 senteces describe how propanic acid and propanoate
anion can be used to make a buffer solution if the ka of propanic
acid is 1.34 x 10^-5
b)determine the ph if the concetration of propanic acid was 1.3
x10^-3 M and the concentration of propanoate was 1.8x10^-2 M. Is
this pH in the rage of the buffer?
c) explain if the pH of the solution in part b is in the range
of thie buffer?

8. Calculate the hydrogen ion concentration of the weak acid in
each of the following solutions. Note that the ionization constants
may be such that the change in electrolyte concentration cannot be
neglected and the quadratic formula or successive approximations
may be required.
(a) 0.0184 M HCNO ( Ka = 3.46 x 10 - 4 ) (b) 0.02173 M CH2 ClCO2 H
( Ka = 1.4 x 10 -3 )

5. (6 pts) The pH of an acetic acid (CH3COOH) solution is 6.20.
Calculate the concentration
of hydronium ion (H3O+, in M) in this solution. (Ka = 1.8 x
10–5)
3
For questions 6-8, consider the titration of of 5.00 mL of 0.450 M
HBr using 0.120 M NaOH as
the Btrant.
6. (6 pts) Calculate the volume of 0.120 M NaOH that must be added
in order to reach the
equivalence point.

Calculate the acetate ion concentration in a
solution prepared by dissolving 5.40×10-3 mol of
HCl(g) in 1.00 L of 1.30 M aqueous acetic
acid (Ka = 1.80×10-5).
Assume that the volume of the solution does not change upon
dissolution of the HCl.

12.) An acid has a Ka = 1.0 x 10-6. At what pH would this acid
and its corresponding salt make a good buffer?
a.) 4
b.) 5
c.) 6
d.) 7
e.) not enough info is given to determine this answer.
13.) A weak acid, HA has a Ka= 1.00 x 10-3. If [HA] = 1.00 M,
what must [A-] be for the pH to be 2.70?
a.) 0.50 M b.) 2.0 M c.) 2.7 M d.) 0.37 M...

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