JEE MAIN - Chemistry (2019 - 10th April Morning Slot - No. 13)
Consider the following statements
(a) The pH of a mixture containing 400 mL of 0.1 M H2SO4 and 400 mL of 0.1 M NaOH will be approximately 1.3
(b) Ionic product of water is temperature dependent.
(c) A monobasic acid with Ka = 10–5 has pH = 5. The degree of dissociation of this acid is 50 %.
(d) The Le Chatelier's principle is not applicable to common-ion effect.
The correct statements are :
(a) The pH of a mixture containing 400 mL of 0.1 M H2SO4 and 400 mL of 0.1 M NaOH will be approximately 1.3
(b) Ionic product of water is temperature dependent.
(c) A monobasic acid with Ka = 10–5 has pH = 5. The degree of dissociation of this acid is 50 %.
(d) The Le Chatelier's principle is not applicable to common-ion effect.
The correct statements are :
(a) and (b)
(a), (b) and (c)
(a), (b) and (d)
(b) and (c)
Explanation
(a) Equivalance of strong acid = 0.1 $$ \times $$ 2 $$ \times $$ 400 = 80
Equivalance of strong base = 0.1 $$ \times $$ 400 = 40
$$ \therefore $$ [H+] of mixture = $${{80 - 40} \over {800}}$$ = $${1 \over {20}}$$
$$ \therefore $$ pH = $$ - \log \left[ {{H^ + }} \right]$$ = $$ - \log \left( {{1 \over {20}}} \right)$$ = 1.3
(b) Ionic product of water increases with increase of temperature because ionisation of water is endothermic.
(c)_10th_April_Morning_Slot_en_13_2.png)
ka = $${{{{10}^{ - 5}} \times c\alpha } \over {c\left( {1 - \alpha } \right)}}$$
$$ \Rightarrow $$ 10-5 = $${{{{10}^{ - 5}} \times \alpha } \over {\left( {1 - \alpha } \right)}}$$
$$ \Rightarrow $$ $${\alpha \over {\left( {1 - \alpha } \right)}}$$ = 1
$$ \Rightarrow $$ $$\alpha $$ = 0.5
$$ \therefore $$ Degree of dissociation($$\alpha $$) = 50%
(d) The Le Chatelier's principle is always applicable to common-ion effect.
Equivalance of strong base = 0.1 $$ \times $$ 400 = 40
$$ \therefore $$ [H+] of mixture = $${{80 - 40} \over {800}}$$ = $${1 \over {20}}$$
$$ \therefore $$ pH = $$ - \log \left[ {{H^ + }} \right]$$ = $$ - \log \left( {{1 \over {20}}} \right)$$ = 1.3
(b) Ionic product of water increases with increase of temperature because ionisation of water is endothermic.
(c)
ka = $${{{{10}^{ - 5}} \times c\alpha } \over {c\left( {1 - \alpha } \right)}}$$
$$ \Rightarrow $$ 10-5 = $${{{{10}^{ - 5}} \times \alpha } \over {\left( {1 - \alpha } \right)}}$$
$$ \Rightarrow $$ $${\alpha \over {\left( {1 - \alpha } \right)}}$$ = 1
$$ \Rightarrow $$ $$\alpha $$ = 0.5
$$ \therefore $$ Degree of dissociation($$\alpha $$) = 50%
(d) The Le Chatelier's principle is always applicable to common-ion effect.
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