Question

Which of the following are capable of forming a buffer solution? What is [H_3O^+] for a buffer solution that is 0.200 M in acid and 0.500 M in the corresponding salt if the weak acid Ka = 5.80 Times 10^-7? In the following reaction, identify the oxidizing agent and reducing agent; write the oxidation and reduction half-reactions for the equation.

Answer 1

7) we know that

a buffer solution is formed between

a weak acid and its conjugate base

and

a weak base and its conjugate acid

a) Nh3 and NH4Cl

NH3 is a weak base and NH4+ is its conjugate acid

so

this combination can form a buffer

b) HN03 is a strong acid

so

no buffer

c) HBr and MgCl2 has no relation

so

no buffer

d) H2C03 is a weak acid and HC03- is its conjugate base

so

a buffer is formed

so

the answer is a and d

8)

we know that for a buffer

pH = pKa + log [salt / acid]

also

pKa = -log Ka

so

pH = -log Ka + log [salt / acid ]

pH = -log 5.8 x 10-7 + log [ 0.5 / 0.2 ]

pH = 6.6345

now

pH = -log [H30+}

so

6.6345 = -log [H30+]

[H30+] = 2.32 x 10-7

so

[H30+] = 2.32 x 10-7 M

9) given reaction is

Cl2 + 2 KI ---> 2 KCl + I2

a) oxidizing agent is the one which undergoes reduction

so

Cl2 is the oxidizing agent

and

KI is the reducing agent

b) oxidation half reaction :

2I- ----> I2 + 2e-

reduction half reaction :

Cl2 + 2e- ---> 2Cl-