1099+ Important Chemistry MCQ Questions Answers

Q:

Temporary hardness is due to the presence of

A) Calcium carbonate	B) calcium bicarbonate
C) magnesium sulphate	D) calcium sulphate

Answer & Explanation Answer: B) calcium bicarbonate

Explanation:

Temporary hardness is due to the presence of soluble bicarbonates of calcium and magnesium in water. Permanent hardness is due to the presence of sulphates and chlorides of calcium and magnesium.

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Q:

The electrochemical cell stops working after some time because ________

A) Electrode potential of both the electrodes becomes zero	B) One of electrodes completely vanishes
C) Electrode potential of both electrodes equalizes	D) The reaction reverses its direction

Answer & Explanation Answer: C) Electrode potential of both electrodes equalizes

Explanation:

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Q:

The entropy change involved in the isothermal reversible expansion of 2 moles of an ideal gas from a volume of 10 $d m^{3}$ at 27°C is to a volume of 100 $d m^{3}$

A) 42.3 J/ mole / K	B) 38.3 J/ mole / K
C) 35.8 J/ mole / K	D) 32.3 J/ mole / K

Answer & Explanation Answer: B) 38.3 J/ mole / K

Explanation:

$∆ s = n R \ln \frac{v 2}{v 1}$

$= 2.303 n R \log \frac{v 2}{v 1}$ = $2.303 \times 2 \times 8.314 \times \log (\frac{100}{10})$ = $38.3 J$ $m o l^{- 1}$ $k^{- 1}$

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Q:

' Misch metal ' is widely used in manufacture of which of the following

A) Material of car brake	B) Smoke detectors
C) Cigarette lighters	D) Emergency lights

Answer & Explanation Answer: C) Cigarette lighters

Explanation:

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Q:

What is the element present in urea

A) C,H,O	B) C,N,O
C) C,N,H	D) C,O,N,H

Answer & Explanation Answer: D) C,O,N,H

Explanation:

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Q:

Which one of the following elements is essential for construction is nuclear reactors

A) Cobalt	B) Nickel
C) Zirconium	D) Tungsten

Answer & Explanation Answer: C) Zirconium

Explanation:

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Q:

When water freezes its density

A) decreases	B) remains constant
C) increases	D) become zero

Answer & Explanation Answer: A) decreases

Explanation:

When water freezes its density decreases.

Water at ordinary temperatures contracts and increases in density as it is cooled, like most substances. But at about 4°C it reaches a maximum density and then decreases in density as it approaches the freezing point.

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Q:

The reduction potential of hydrogen half-cell will be negative if :
(1) $P (H_{2})$ = 2 atm and [H+] = 2.0 M
(2) $P (H_{2})$ = 1 atm and [H+] = 2.0 M
(3) $P (H_{2})$ = 1 atm and [H+] = 1.0 M
(4) $P (H_{2})$ = 2 atm and [H+] = 1.0 M

A) Option 1	B) Option 2
C) Option 3	D) Option 4

Answer & Explanation Answer: D) Option 4

Explanation:

$H^{+} - e^{-} \to \frac{1}{2} H_{2}$

Apply Nernst equation

$E = 0 - \frac{0.059}{1} \log (\frac{P H_{2}^{\frac{1}{2}}}{[H^{+}]})$

$E = - \frac{0.059}{1} \log (\frac{2^{\frac{1}{2}}}{1})$

Therefore E is Negative

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