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Standard XII

Chemistry

Acidic Buffer Action

How many mole...

Question

How many moles of sodium propionate $(C H_{3} C H_{2} C O O N a)$ should be added to one litre of an aqueous solution containing 0.02 mole of propionic acid $(C H_{3} C H_{2} C O O H)$ to obtain a buffer solution of $p H = 5.87$ ?
Dissociation constant of propionic acid $K_{a}$ at $25^{\circ} C$ is $1.34 \times 10^{- 5}$

Take $l o g (1.34) = 0.13$

0.1 mol

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0.2 mol

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0.01 mol

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0.02 mol

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Solution

The correct option is B 0.2 mol
Here for an acidic buffer ,
Sodium propionate is the salt and propionic acid is the acid.
Since volume of the solution is 1 L.
So,
moles = concentration
$[C H_{3} C H_{2} C O O H] = 0.02 M$

$p K_{a} = - l o g (K_{a}) p K_{a} = - l o g (1.34 \times 10^{- 5}) p K_{a} = (5 - 0.13) = 4.87$

$p H = p K_{a} + l o g \frac{[s a l t]}{[a c i d]} p H = p K_{a} + l o g (\frac{[C H_{3} C H_{2} C O O N a]}{[C H_{3} C H_{2} C O O H]}) 5.87 = 4.87 + l o g (\frac{[C H_{3} C H_{2} C O O N a]}{0.02}) 1 = l o g (\frac{[C H_{3} C H_{2} C O O N a]}{0.02}) 10^{1} = \frac{[C H_{3} C H_{2} C O O N a]}{0.02} [C H_{3} C H_{2} C O O N a] = 0.2 M$
$∴$ moles of sodium propionate = concentration= 0.2 mol

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Similar questions

Q. How many moles of sodium propionate

(C H_{3} C H_{2} C O O N a)

should be added to one litre of an aqueous solution containing 0.02 mole of propionic acid

(C H_{3} C H_{2} C O O H)

to obtain a buffer solution of

p H = 5.87

?
Dissociation constant of propionic acid

K_{a}

25^{\circ} C

1.34 \times 10^{- 5}

Take

l o g (1.34) = 0.13

Q. What will be the new

p H

0.01 m o l

H C l

is added to a

1 L

buffer solution that is

0.02 M

in propionic acid

(C H_{3} C H_{2} C O O H)

and

0.015 M

in sodium propionate

(C H_{3} C H_{2} C O O N a)

?
Dissociation constant

K_{a}

of propionic acid at

25^{\circ} C

1.34 \times 10^{- 5}

(Take

l o g (1.34) = 0.13

)

Q. I. How many moles of sodium propionate should be added to one litre of an aqueous solution contain

0.02

mole of propionic acid to obtain a buffer solution of

p H

4.7

?
II. What will be the

p H

0.0005

mole of hydrogen chloride is dissolved in the above buffer solution?
III. Compare the last

p H

value with the

p H

of a

0.01

molar

H C l

solution.
Assume that dissociation constant of propionic acid,

25^{o} C

1.00 \times 10^{- 5}

Q. What amount of sodium propanoate should be added to one litre of an aqueous solution containing

0.02

mole of propanoic acid

[K a = 1.34 \times 10^{- 5}

25^{o} C]

to obtain a buffer solution of pH

4.75

Q. What amount of sodium propanoate should be added to one litre of an aqueous solution containing

0.02 m o l e

of propanoic acid

(K_{a} = 1.34 \times 10^{- 5}

25^{\circ} C

) to obtain a buffer solution of

p H 4.75

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Acidic Buffer Action

Standard XII Chemistry

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How many moles of sodium propionate (CH3CH2COONa) should be added to one litre of an aqueous solution containing 0.02 mole of propionic acid(CH3CH2COOH) to obtain a buffer solution of pH=5.87 ? Dissociation constant of propionic acid Ka at 25∘C is 1.34×10−5 Take log(1.34)=0.13