Equilibrium Test

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Equilibrium Test - 13

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following mixture is not a buffer solution?

A
100ml of 0.5 $$N - CH_{3}COOH +$$ 100 ml of 0.05 N- NaOH

B
100ml of 0.5 $$N-NH_{4}OH +$$ 100ml of 0.5 N-HCl

C
100 ml of 0.5 $$N-NH_{4}OH +$$ 10 ml of 0.5 $$N-H_{2}SO_{4}.$$

D
300 ml of 0.5 $$N-NH_{4}OH +$$ 200 ml of 0.5 $$N-HNO_{3}$$

Solution

Basic buffer solution is prepared by mixing a weak base and its salt with strong acid.
In the mixture containing 100ml of 0.5 N $$NH_4OH$$ + 100ml of 0.5 N-HCl, equal number of moles of ammonium hydroxide and hydrochloric acid are present.
They completely neutralize each other to form salt ammonium chloride. Thus weak base ammonium hydroxide is not present in the mixture.
Hence, this mixture is not a buffer solution.
Question 2
1 / -0

1M NaCl and 1M HCl are present in an aqueous solution . The solution is:

A
Not a buffer solution with pH <7

B
Not a buffer solution with pH >7

C
A buffer solution with pH <7

D
A buffer solution with pH >7

Solution

Buffer can accept and donate protons at the same time and $$HCl$$ is an acid. So, it has $$pH<7$$.
So, this is not a buffer and the solution will be acidic.

Hence, the correct option is $$A$$
Question 3
1 / -0

The $$pH$$ of a solution obtained by mixing $$50\: ml$$ of $$0.4N$$ $$NH_{4}Cl$$ and $$50\: ml$$ of $$0.2 N$$ $$NaOH$$ is:

A
$$- log\ 2$$

B
$$-log\ (0.2)$$

C
$$1.0$$

D
$$2.0$$

Solution

The expression for the hydrogen ion concentration is as given below.

$$[H^+]= \dfrac {V_bN_b-V_aN_a} {V_a+V_b}$$

Substitute values in the above expression,

$$[H^+]= \dfrac {50 \times 0.4-50 \times0.2} {50+50}=0.1$$

$$pH=-log\ [H^+]=-log\ (0.1)=1$$
Question 4
1 / -0

Assertion: A buffer solution has a capacity to resist the change in pH value on an addition of a small amount of acid or base to it.
Reason: An aqueous solution of ammonium acetate can act as buffer.

A
Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

B
Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

C
Assertion is correct but Reason is not correct

D
Assertion is not correct but Reason is correct

E
Both Assertion and Reason are not correct

Solution

salts of weak-acid and weak-base can act as buffer solution.
Question 5
1 / -0

Assertion: A mixture of $$CH_3COOH$$ and $$CH_3COONH_4$$ is not a buffer solution.
Reason: An acidic buffer contains the mixture of a weak acid and its salt with a strong base.

A
Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

B
Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

C
Assertion is correct but Reason is not correct

D
Assertion is not correct but Reason is correct

E
Both Assertion and Reason are not correct

Solution

Acidic buffer solution is prepared by mixing a weak acid and its salt with strong base. A solution containing weak acid and its salt with weak base is not a buffer solution.
Ammonium acetate is a salt of weak acid and weak base. Hence, mixture of acetic acid and ammonium acetate is not a buffer solution.
Question 6
1 / -0

$$C_{2}H_{4}(g) + H_{2}(g)\leftrightharpoons C_{2}H_{6}(g);\ \Delta H = - 31.7 \ kcal$$.
The equilibrium concentration of $$C_{2}H_{4}$$ in the following reaction can be increased by:

A
removal of $$C_{2}H_{6}$$

B
addition of $$H_{2}$$

C
increase in temperature

D
increase in pressure

Solution

Negative value of the enthalpy change $$(\Delta H = - 31.7 K)$$ for the reaction $$C_{2}H_{4}(g) + H_{2}(g)\leftrightharpoons C_{2}H_{6}(g)$$ indicates that it is an exothermic reaction.

When the temperature of an exothermic reaction is increased, the reaction will proceed in the backward direction so as to absorb heat and nullify the effect of increasing temperature. This will decrease the value of the equilibrium constant $$K_c$$. In other words, the equilibrium will shift to left.

Thus, to increase the equilibrium concentration of $$C_{2}H_{4}$$, the temperature should be increased.
Question 7
1 / -0

The equilibrium constant of a reaction at $$298 \:K$$ and $$1000\: K$$ is $$5 \times 10^{-3}$$ and $$2\times 10^{-3}$$ respectively. The $$\Delta H$$ for the reaction is:

A
positive

B
negative

C
either positive or negative

D
zero

Solution

With the increase in temperature from $$298 \:K$$ to $$1000 \:K$$, the value of the equilibrium constant decreases from $$5 \times 10^{-3}$$ to $$2\times 10^{-3}$$.

Thus, as the temperature increases, the equilibrium shifts to the left direction. This is possible for an exothermic reaction.

Thus, the reaction is an exothermic reaction having a negative value of enthalpy change.
Question 8
1 / -0

The reaction $$A + B \leftrightharpoons C + D + heat$$, has reached equilibrium. It is possible to make the reaction to proceed forward:

A
by adding more of $$C$$

B
by adding more of $$D$$

C
by raising the temperature of the system

D
by lowering the temperature

Solution

The reaction $$A + B \Leftrightarrow C + D + heat$$ is an exothermic reaction.

According to Le Chatelier's principle, as the temperature is lowered, the reaction will proceed in the direction so as to liberate heat and nullify the effect of lowering the temperature.

Hence, the reaction will proceed in the forward direction by lowering the temperature.
Question 9
1 / -0

Assertion: pH of blood does not change in spite of taking acidic foods.
Reason: Blood behaves as a buffer solution.

A
Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

B
Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

C
Assertion is correct but Reason is not correct

D
Assertion is not correct but Reason is correct

E
Both Assertion and Reason are not correct

Solution

Blood contains a mixture of $$H_{2}CO_{3}$$ and $$HCO_{3}^{-} $$ which acts as acidic buffer solution.
Thus blood has the tendency to resist changes in pH when small quantities of acid or base are added.
Question 10
1 / -0

In the system $$CaF_{2} (s) \rightleftharpoons Ca^{2+}(aq) + 2F^{-}(aq)$$, if the concentration of $$Ca^{2+}$$ is increased by four times, then the equilibrium concentration of $$F^{-}$$ will be changed to:

A
one half of its initial value

B
twice the initial value

C
one fourth of its initial value

D
thrice of its initial value

Solution

The equilibrium reaction is as follows:
$$CaF_{2} (s) \rightleftharpoons Ca^{2+}(aq) + 2F^{-}(aq)$$.

The expression for the equilibrium constant is $$K=[Ca^{2+}][F^-]^2$$.

Let $$X$$ and $$Y$$ be the initial concentrations of $$[Ca^{2+}]$$ and $$[F^-]$$ ions.

The expression for the equilibrium constant will be $$K=[Ca^{2+}][F^-]^2=XY^2$$ ......$$(1)$$

When the concentration of the $$Ca^{2+}$$ ions is increased four times, the expression for the new equilibrium constant will be $$K=[Ca^{2+}][F^-]^2=4X\times [F^-]^2$$ ...... $$(2)$$

The magnitude of the equilibrium constant is not affected by the changes in concentrations of reactants and products.

Thus, from $$(1)$$ and $$(2)$$, we get $$K=XY^2=4X\times [F^-]^2$$
$$\implies [F^-]= \dfrac {Y} {2}$$.

Thus, the equilibrium concentration of $$F^{-}$$ ions is reduced to one half its original value.

Hence, the correct option is $$\text{A}$$

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Equilibrium Test - 13

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Equilibrium Test - 13

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Question 1

100ml of 0.5 $$N - CH_{3}COOH +$$ 100 ml of 0.05 N- NaOH

100ml of 0.5 $$N-NH_{4}OH +$$ 100ml of 0.5 N-HCl

100 ml of 0.5 $$N-NH_{4}OH +$$ 10 ml of 0.5 $$N-H_{2}SO_{4}.$$

300 ml of 0.5 $$N-NH_{4}OH +$$ 200 ml of 0.5 $$N-HNO_{3}$$

Solution

Question 2

Not a buffer solution with pH <7

Not a buffer solution with pH >7

A buffer solution with pH <7

A buffer solution with pH >7

Solution

Question 3

$$- log\ 2$$

$$-log\ (0.2)$$

$$1.0$$

$$2.0$$

Solution

Question 4

Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

Assertion is correct but Reason is not correct

Assertion is not correct but Reason is correct

Both Assertion and Reason are not correct

Solution

Question 5

Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

Assertion is correct but Reason is not correct

Assertion is not correct but Reason is correct

Both Assertion and Reason are not correct

Solution

Question 6

removal of $$C_{2}H_{6}$$

addition of $$H_{2}$$

increase in temperature

increase in pressure

Solution

Question 7

positive

negative

either positive or negative

zero

Solution

Question 8

by adding more of $$C$$

by adding more of $$D$$

by raising the temperature of the system

by lowering the temperature

Solution

Question 9

Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

Assertion is correct but Reason is not correct

Assertion is not correct but Reason is correct

Both Assertion and Reason are not correct

Solution

Question 10

one half of its initial value

twice the initial value

one fourth of its initial value

thrice of its initial value

Solution

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