Question

7. If H.PO, has K. -6.83 x 10', and H.CO, has K, -5.8 x 10", which is the weaker acid? Circle your answer and explain how you know. (pt) 8. For a solution with pH = 9.74, calculate the following: 3ps) [OH) = pOH - 9. (pes total) a. A solution of a weak acid with concentration - 0.11 M. is 8.8 % ionized. Calculate its K, value b. Calculate the K, value of a 0.060 M solution of a monoprotic acid with [H'] -2.7 x 10M

please help with numbers 7, 8 and 9 showing work

Answer 1

7) We can compare strength of two acids on the basis of K a value. We know that, higher the Ka value stronger will be acid and vice versa.

If we compare Ka values of H2PO4 acid and carbonic acid, it is found that Ka value of H2PO4 acid is significantly large than Ka value of Carbonic acid. Hence, H2PO4 acid is a strong acid and carbonic acid is a weak acid.

8) We have , pH = - log [H⁺]

$\therefore$ [H⁺] = 10 ^-pH

We have, pH = 9.74

$\therefore$ [H⁺] = 10 ^{- 9.74} = 1.820 $\times$ 10 ^-10 M

We have relation, [H⁺] [ OH ^-] = K w = 1.00 $\times$ 10 ^-14

$\therefore$ [ OH ^-] = 1.00 $\times$ 10 ^-14 /  [H⁺]

$\therefore$ [ OH ^-] = 1.00 $\times$ 10 ^-14 / 1.820 $\times$ 10 ^-10

[ OH ^-] = 5.49 $\times$ 10 ^-05 M

We have, pOH = - log [ OH ^-] = - log 5.49 $\times$ 10 ^-05 = 4.26

9)

a) Consider dissociation of weak acid HA .

HA (aq) $\rightleftharpoons$ H ⁺ (aq) + A ^- (aq)

For above reaction, K a = [H ⁺] [A ^- ] / [HA] -------------------> (1)

We know that, % dissociation = $\alpha$ $\times$ 100

Where , $\alpha$ is degree of dissociation

Hence, $\alpha$ = % dissociation / 100 = 8.8 /100 = 0.088

We have, [H ⁺] = $\alpha$ $\times$ C where C is a molar concentration of acid.

[H ⁺] = 0.088 $\times$ 0.11 M = 9.68 $\times$ 10 ^-03 M = [A ^- ]

$\therefore$ K a = [H ⁺] [A ^- ] / [HA]

K a = ( 9.68 $\times$ 10 ^-03 ) ( 9.68 $\times$ 10 ^-03 ) / 0.11

K a = 8.52 $\times$ 10 ^-04

b)

Consider dissociation of weak acid HA .

HA (aq) $\rightleftharpoons$ H ⁺ (aq) + A ^- (aq)

For above reaction, K a = [H ⁺] [A ^- ] / [HA]

We have ,[HA] = 0.060 M , [H ⁺] = [A ^- ] = 2.7 $\times$ 10 ^-12 M  

$\therefore$ K a = ( 2.7 $\times$ 10 ^-12 ) ( 2.7 $\times$ 10 ^-12 ) / 0.060 = 1.22 $\times$ 10 ^-22 M

Image is not clear , if value 2.7 $\times$ 10 ^-12 is not correct make changes by taking correct value.