Equilibrium Test

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Equilibrium Test - 12

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Weekly Quiz Competition

Question 1
1 / -0

The $$pH$$ of a mono-acidic base is 12.6990. The molarity of the base is:

A
0.02 moles/litre

B
0.05 moles/litre

C
0.5 moles/litre

D
0.2 moles/litre

Solution

$$pH+pOH=14$$.

Thus, $$pOH=14-pH=14-12.6690=1.3310$$.

But, $$pOH=-log[OH^-]$$.

Hence, $$[OH^-]=0.05\ M$$.

This is equal to the molarity of base.

Option B is correct.
Question 2
1 / -0

A weak mono acidic base is $$5$$% ionized in $$0.01 M$$ solution. The hydroxide ion concentration in the solution is:

A
$$5 \times 10^{-2}$$

B
$$5 \times 10^{-4}$$

C
$$5 \times 10^{-10}$$

D
$$2 \times 10^{-11}$$

Solution

Let the monoacidic base be $$BOH$$.

Given that $$c=0.01M$$ and $$\alpha =0.05$$.

SInce $$\alpha\ll 1$$

On dissociation,
$$BOH\leftrightharpoons B^{+}+OH^{-}$$

$$c $$ $$ - $$ $$ - $$
$$c(1-\alpha)$$ $$ c\alpha$$ $$ c\alpha $$

The concentration of $$OH^{-}$$ is given by $$c\alpha$$.

$$\Rightarrow \left [ OH^{-} \right ]=0.01\times 0.05 $$

$$\Rightarrow \left [ OH^{-} \right ]=5 \times 10^{-4}$$.

Hence, option B is correct.
Question 3
1 / -0

Buffer solution is prepared by mixing:

A
Strong acid + its salt of strong base

B
Weak acid + its salt of strong base.

C
Strong acid + its salt of weak base

D
None of the above

Solution

Acidic buffer solution is prepared by mixing a weak acid and its salt with strong base.
Fro example, a mixture of acetic acid (a weak acid) and sodium acetate (salt with strong base sodium hydroxide) acts as buffer.
Question 4
1 / -0

The strength of acid is highest in:

A
$$p K_{a}=6 $$

B
$$p K_{a}=5 $$

C
$$p K_{a}=10 $$

D
$$p K_{a}= 1 $$

Solution

$$ pK_a = -log\:K_a $$

Higher the $$K_a$$, higher is the strength of the acid.

For higher $$K_a$$, $$pK_a$$ value is smaller.

Option D is correct.
Question 5
1 / -0

Buffer solution can be obtained by mixing aqueous solution of _______.

A
Sodium acetate and excess of HCl

B
Sodium acetate and acetic acid

C
Sodium chloride and HCl

D
Acetic acid and excess of NaOH

Solution

A mixture of acetic acid (a weak acid) and sodium acetate ( its salt with strong base sodium hydroxide) acts as acidic buffer.
Option A, C and D does not contain weak acid/weak base and its salt thus it does not form buffer solution.
Question 6
1 / -0

5.6 grams of KOH $$(M. wt = 56)$$ is present in 1 litre of solution. Its pH is:

A
1

B
13

C
14

D
0

Solution

Molarity of KOH solution = $$=\cfrac {\text{Weight}} {\text{Molecular weight} \times \text{volume}}= \cfrac {5.6} {56 \times 1}=0.1$$ M.

This is equal to $$[OH^-]$$.

$$pOH=-log[OH^-]=-log( 0.1 )=1$$

$$pH=14-pOH=14-1=13$$.

Hence, option B is correct.
Question 7
1 / -0

Solubility of $$AgCl$$ will be minimum in ___________.

A
0.01 M $$Na_{2} SO_{4}$$

B
0.01 M $$Ca Cl_{2}$$

C
Pure water

D
0.001 M $$Ag NO_{3}$$
Question 8
1 / -0

8 gram of NaOH is mixed with 9.8 gram of $$H_{2}SO_{4}$$, the pH of the solution is:

A
more than 7

B
7

C
less than 7

D
cant be said

Solution

8 gram (0.2 mole) of NaOH (molecular weight 40 g/mol) completely neutralizes 9.8 gram (0.1 mole) of $$H_2SO_4$$ (molecular weight 98 g/mol).

$$NaOH\to Na^++OH^-$$

$$H_2SO_4\to 2H^++SO_4^{2-}$$

Since the molar concentration of both $$OH^-$$ and $$H^+$$ are same, the resulting solution will be neutral. Its pH will be 7.
Question 9
1 / -0

$$pH$$ of a solution produced when aqueous solution of $$pH=6$$ is mixed with an equal volume of an aqueous solution of $$pH=3$$ is about:

A
$$4.3$$

B
$$3.3$$

C
$$4.0$$

D
$$4.5$$

Solution

The $$pH$$ of solution is negative logarithm of hydrogen ion concentration.
$$pH=-log[H^+]$$

Hence, $$[H^+]=10^{-pH}$$

$$pH=3$$ and $$pH=6$$ corresponds to hydrogen ion concentrations of $$0.001 M$$ and $$0.000001 M$$ respectively.

Assuming $$1 L$$ of each solution is mixed,
the concentration of resulting solution is $$ \dfrac{0.001 M + 0.000001 M}{2} = 0.0005M$$.

$$pH = -log [H^+] = -log\left( 0.0005\right)=3.3$$

Option B is correct.
Question 10
1 / -0

Assertion:
The pH of the buffer solution does not change when an acid or a base is added.

Reason:
Buffer solution consists of a 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

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Equilibrium Test - 12

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Equilibrium Test - 12

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Question 1

0.02 moles/litre

0.05 moles/litre

0.5 moles/litre

0.2 moles/litre

Solution

Question 2

$$5 \times 10^{-2}$$

$$5 \times 10^{-4}$$

$$5 \times 10^{-10}$$

$$2 \times 10^{-11}$$

Solution

Question 3

Strong acid + its salt of strong base

Weak acid + its salt of strong base.

Strong acid + its salt of weak base

None of the above

Solution

Question 4

$$p K_{a}=6 $$

$$p K_{a}=5 $$

$$p K_{a}=10 $$

$$p K_{a}= 1 $$

Solution

Question 5

Sodium acetate and excess of HCl

Sodium acetate and acetic acid

Sodium chloride and HCl

Acetic acid and excess of NaOH

Solution

Question 6

1

13

14

0

Solution

Question 7

0.01 M $$Na_{2} SO_{4}$$

0.01 M $$Ca Cl_{2}$$

Pure water

0.001 M $$Ag NO_{3}$$

Question 8

more than 7

7

less than 7

cant be said

Solution

Question 9

$$4.3$$

$$3.3$$

$$4.0$$

$$4.5$$

Solution

Question 10

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

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