Equilibrium Test

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Equilibrium Test - 33

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Question 1
1 / -0

A buffer solution is used in:

A
preparation of potash alum

B
the removal of $${ PO }_{ 4 }^{ 3- }$$ ions

C
increasing the pH value of a solution

D
precipitation of $$Cr{ \left( OH \right) }_{ 3 }$$ from $$Cr{ Cl }_{ 3 }$p

Solution

$$PO_4^{3-}$$ removal columns are designed to remove $$PO_4^{3-}$$ from a buffer solution. For example, the $$PO_4^{3-}$$ concentration can be reduced from $$10mM$$ to lower than $$0.001mM$$. The principle of phosphate removal is based on interactions between $$PO_4^{3-}$$ and column resin. The $$PO_4^{3-}$$ stays on the column. Other buffer components including regular buffer salts and non-charged molecules such as sugar and glycerol do not bind to the resin, therefore they stay in the sample solution.
Question 2
1 / -0

The $$pH$$ of an aqueous solution of a $$0.1M$$ solution of a weak monoprotic acid which is $$1$$% ionised is:

A
$$1$$

B
$$2$$

C
$$3$$

D
$$11$$

Solution

Concentration of solution $$= C = 0.1M$$

Dissociation is $$\alpha=0.01$$

After dissociation, the concentration of $$H^+$$ ions will be $$C\alpha=0.1\times 0.01=10^{-3}=[H^+]$$

We know the fomrula for pH as
$$pH=-log[H^+]=-log(10^{-3})=+3$$
Question 3
1 / -0

Which of the following expressions is not true?

A
$$\left[ { H }^{ + } \right] =\left[ { OH }^{ - } \right] =\sqrt { { K }_{ w } } $$ for a neutral solution

B
$$\left[ { H }^{ + } \right] >\sqrt { { K }_{ w } } $$ and $$\left[ { OH }^{ - } \right] <\sqrt { { K }_{ w } } $$ for an acidic solution

C
$$\left[ { H }^{ + } \right] <\sqrt { { K }_{ w } } $$ and $$\left[ { OH }^{ - } \right] >\sqrt { { K }_{ w } } $$ for an alkaline solution

D
$$\left[ { H }^{ + } \right] =\left[ { OH }^{ - } \right] ={ 10 }^{ -7 }M$$ for a neutral solution at all temperatures

Solution

For a neutral solution at $$25^0C$$ $$pH$$ and $$pOH$$ are both equal to 7 so $$[H^{+}]=[OH^{-}]=\sqrt{K_w}$$.
For an acidic solution $$pH<7$$ so $$[H^{+}]>\sqrt{K_w}$$. and $$[OH^{-}]<\sqrt{K_w}$$.As the temperature increases dissociation will increase so $$pH$$ of neutral solution will decrease.So $$[H^{+}] $$ is not equal to $$[OH^{-}] $$ or$$\sqrt{K_w}$$ at all temperatures.
Question 4
1 / -0

Which one does not give a buffer solution?

A
Ammonia and sodium hydroxide in water

B
Sodium acetate and acetic acid in water

C
Ammonia and ammonium chloride in water

D
Sodium acetate and hydrochloric acid in water

Solution

Buffer solution is a mixture of weak acid and its conjugate base or weak base and its conjugate acid. So ammonia(strong base) and sodium hydroxide does not give a buffer.
Question 5
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

$$HCl$$ is strong acid so it cannot make a buffer and $$HCl$$ with $$NaCl$$ have $$pH<7$$.
Question 6
1 / -0

Which of the following statements is correct?

A
$$p{ K }_{ w } $$ increases with increase of temperature

B
$$p{ K }_{ w }$$ decreases with increase of temperature

C
$$p{ K }_{ w }=14$$ at all temperatures

D
$$p{ K }_{ w }=pH $$ at all temperatures

Solution

As temperature increases dissociation will increase so number of $$H^{+}$$ and $$OH^{-}$$ will increase.As $$K_w=[H^{+}][OH^{-}]$$ so $$K_w$$ will increase so $$pK_w$$ will decrease with increase in temperature.
Question 7
1 / -0

The weak acid, $$HA$$ has a $${K}_{a}$$ of $$1.00\times { 10 }^{ -5 }$$. If $$0.1$$ mol of this acid is dissolved in one litre of water, the percentage of acid dissociated at equilibrium is closet to:

A
$$1$$%

B
$$99.9$$%

C
$$0.1$$%

D
$$99$$%

Solution

0.1 mole of acid is dissolved in 1 litre of water means $$[HA]=0.1M$$
Let '$$\alpha$$' be degree of dissociation,
$$HA\rightleftharpoons { H }^{ + }+{ A }^{ - }$$
$$0.1$$
$$0.1(1-\alpha)$$ $$0.1\alpha$$ $$0.1\alpha$$

$${ K }_{ a }=\cfrac { \left[ { H }^{ + } \right] \left[ { A }^{ - } \right] }{ \left[ HA \right] } =\cfrac { { 0.1 }^{ 2 }{ \alpha }^{ 2 } }{ 0.1(1-\alpha) } $$

Let $$\alpha<<1$$ so $$1-\alpha=1$$

$$K_a=0.1\alpha^2=10^{-5}$$

$$\alpha=10^{-2}$$

% of acid dissociated=$$1$$%
Question 8
1 / -0

For dissociation constant $$(K)$$ and ionic product $$({K}_{w})$$ of water which is correct?

A
$$K>{ K }_{ w }$$

B
$${ K }_{ w }>K$$

C
$${ K }_{ w }=K$$

D
None of these

Solution

The value of ionisation constant of water is $$1.8 \times 10^{-16} \text{and} \dfrac{1}{55.55}$$ times that of $$K_w$$, the ionic product of water.
So $$K_w>K$$.
Hence option B is correct.
Question 9
1 / -0

Which mixture forms a buffer when dissolved in $$1\ L$$ of water?

A
$$0.2\ mol\ NaOH+0.2\ mol \ HBr$$

B
$$0.2\ mol \ NaCl+0.3\ mol\ HCl$$

C
$$0.4\ mol\ H{NO}_{2}+0.2\ mol\ NaOH$$

D
$$0.5\ mol\ {NH}_{3}+0.5\ mol\ HCl$$

Solution

(C) $$ 0.4 mol HNO_2 + 0.2 mol NaOH$$ will form a buffer as it is a mixture of weak acid and its conjugate base.
Question 10
1 / -0

The solubility of $${ A }_{ 2 }{ X }_{ 5 }$$ is $$x\ mol\ { dm }^{ -3 }$$. Its solubility product is:

A
$$36{ x }^{ 6 }$$

B
$$64\times { 10 }^{ 4 }{ x }^{ 7 }$$

C
$$126{ x }^{ 7 }$$

D
$$1.25\times { 10 }^{ 4 }{ x }^{ 7 }$$

Solution

Let the solubility be $$S.$$
$${ As }_{ 2 }X_{ 3 }\leftrightharpoons 2As^{ 5+ }+5X^{ 2- }\\ \quad \quad \quad \quad 2S\quad \quad \quad 5S$$
Solubility product is
$$K_{ sp }=[As^{ 5+ }]^{ 2 }\times [S^{ 2- }]^{ 5 }\\$$
Let $$[{ As }_{ 2 }S_{ 5 }]=S,[As^{ 5+ }]=2S, [S^{ 2- }]=5S\\ Ksp=(2S)^{ 2 }\times (5S)^{ 5 }=4S^{ 2 }\times 3125S^{ 5 }=12500S^{ 7 }$$

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Equilibrium Test - 33

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Equilibrium Test - 33

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SHARING IS CARING

Question 1

preparation of potash alum

the removal of $${ PO }_{ 4 }^{ 3- }$$ ions

increasing the pH value of a solution

precipitation of $$Cr{ \left( OH \right) }_{ 3 }$$ from $$Cr{ Cl }_{ 3 }$p

Solution

Question 2

$$1$$

$$2$$

$$3$$

$$11$$

Solution

Question 3

$$\left[ { H }^{ + } \right] =\left[ { OH }^{ - } \right] =\sqrt { { K }_{ w } } $$ for a neutral solution

$$\left[ { H }^{ + } \right] >\sqrt { { K }_{ w } } $$ and $$\left[ { OH }^{ - } \right] <\sqrt { { K }_{ w } } $$ for an acidic solution

$$\left[ { H }^{ + } \right] <\sqrt { { K }_{ w } } $$ and $$\left[ { OH }^{ - } \right] >\sqrt { { K }_{ w } } $$ for an alkaline solution

$$\left[ { H }^{ + } \right] =\left[ { OH }^{ - } \right] ={ 10 }^{ -7 }M$$ for a neutral solution at all temperatures

Solution

Question 4

Ammonia and sodium hydroxide in water

Sodium acetate and acetic acid in water

Ammonia and ammonium chloride in water

Sodium acetate and hydrochloric acid in water

Solution

Question 5

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 6

$$p{ K }_{ w } $$ increases with increase of temperature

$$p{ K }_{ w }$$ decreases with increase of temperature

$$p{ K }_{ w }=14$$ at all temperatures

$$p{ K }_{ w }=pH $$ at all temperatures

Solution

Question 7

$$1$$%

$$99.9$$%

$$0.1$$%

$$99$$%

Solution

Question 8

$$K>{ K }_{ w }$$

$${ K }_{ w }>K$$

$${ K }_{ w }=K$$

None of these

Solution

Question 9

$$0.2\ mol\ NaOH+0.2\ mol \ HBr$$

$$0.2\ mol \ NaCl+0.3\ mol\ HCl$$

$$0.4\ mol\ H{NO}_{2}+0.2\ mol\ NaOH$$

$$0.5\ mol\ {NH}_{3}+0.5\ mol\ HCl$$

Solution

Question 10

$$36{ x }^{ 6 }$$

$$64\times { 10 }^{ 4 }{ x }^{ 7 }$$

$$126{ x }^{ 7 }$$

$$1.25\times { 10 }^{ 4 }{ x }^{ 7 }$$

Solution

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