A ) Zn(OH) 2 OH - Zn(OH) 4 -2 1 points B ) Which of the following statements abo

Question

A)

Zn(OH)2

OH-

Zn(OH)4-2

1 points   

B)

Which of the following statements about buffers is/are true?

1 - A buffered solution containing 1.0 M HOCl and 1.0 M NaOCl has a larger buffer capacity than one containing 0.10 M HOCl and 0.10 M NaOCl.

2 - In a buffer, when the [H+] < Ka, the acid concentration is smaller than the conjugate base concentration.

3 - When a small amount of strong acid or base is added to a buffer, the pH changes a lot.

1

2

3

1 and 2

1 and 3

1 points   

C)

Calculate the pH of a buffer solution which is 0.23 M in HNO2 and 0.34 M in NaNO2.
Ka of HNO2 = 4.6x10-4 at 25oC

2 points   

D)

An acetic acid/sodium acetate buffer is made that is 0.57 M in HAc and 0.57 M in NaAc. Calculate the pH after 0.075 mol of KOH is added to 1.0 L of the buffer. (Assume no volume change.)

Zn(OH)2

OH-

Zn(OH)4-2

Explanation / Answer

A ) lewis basw b . OH-

B ) b) 2

(C)

Calculate the pH of a buffer solution which is 0.23 M in HNO2 and 0.34 M in NaNO2.
Ka of HNO2 = 4.6x10-4

pKa = -logKa = -log (4.6x10-4 ) = 3.34

pH = pKa + log [NaNO2/HNO2]

pH = 3.34   + log [0.34 / 0.23]

pH = 3.51

D)

pKa of AcOH = 4.74

molarity of KOB base (C)= 0.075 / 1 = 0.075 M

on addition of base to acidic buffer acid concentration decreases and salt concentration increases

pH = pKa + log [salt + C / acid - C]

pH = 4.74 + log [0.57 + 0.075 / 0.57 -0.075]

pH = 4.86

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