Chemistry Test

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Chemistry Test - 11

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Weekly Quiz Competition

Question 1
1 / -0

The standard Gibb's free energy of the following reaction at 25^oC is 38484 J.

PCl₅ (g) PCl₃ (g) + Cl₂ (g)

The value of equilibrium constant is

A
1.5 * 10^-7

B
0.18 * 10^-7

C
1.8 * 10^-7

D
None of these

Solution
Question 2
1 / -0

If equivalent conductance of 1 M benzoic acid is 12.8 ohm^-1 cm², and the values of conductance of benzoate ion and H⁺ ion respectively are 42 and 288.42 ohm^-1 cm², then its degree of dissociation is:

A
39%

B
3.9%

C
0.35%

D
0.039%

Solution
Question 3
1 / -0

The resistance of 0.01 N solution of an electrolyte was found to be 210 ohm at 298 K, using a conductivity cell of cell constant 0.66 cm⁻¹. The equivalent conductance of the solution is

A
3.14 mho⁻²cm²eq⁻¹

B
314.28 mho⁻¹cm²eq⁻¹

C
31.4 mho cm²eq⁻¹

D
314.28 mho cm²eq⁻¹

Solution
Question 4
1 / -0

Directions: The following question is based on the paragraph given below:
Chemical reactions involve interaction of atoms and molecules. A large number of atoms / molecules (approximately 6.023 ×10²³ ) are present in a few grams of any chemical compound varying with their atomic /molecular masses. To handle such large numbers conveniently, the mole concept was introduced.
This concept has implications in diverse areas such as analytical chemistry, biochemistry electrochemistry and radiochemistry. The following example illustrates a typical case, involving chemical/electrochemical reaction, which requires a clear understanding of the mole concept. A 4.0 molar aqueous solution NaCl is prepared and 500 mL of this solution is electrolysed. This leads to the evolution of chlorine gas at one of the electrodes (Atomic mass : Na = 23, Hg = 200;1 Faraday = 96500 coulombs).
If the cathode is a Hg electrode, the maximum weight (g) of amalgam formed from this solution is

A
200

B
225

C
400

D
446

Solution

In presence of Hg cathode sodium ion will discharge in place of hydrogen gas due to over voltage in the form of amalgams.
Weight of amalgam = 2 × (23 + 200) = 446 g
Question 5
1 / -0

How many coulombs of electricity is required for the complete reduction of MnO₄^- in 500 ml of 0.5 M solution to Mn₂⁺ ions?

A
96500 C

B
1.93 105 C

C
120625 C

D
9.65 * 10⁵ C

Solution
Question 6
1 / -0

The energies of activation for forward and reverse reactions of A2 + B2 → 2AB are 180 kJ mol-1 and 200 kJ mol^-1 respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by 100 kJ mol^-1. The enthalpy change of the reaction (A2 + B2 → 2AB) in the presence of catalyst will be (in kJ mol^-1)

A
280

B
-20

C
300

D
-120

Solution

ΔH does not change due to catalyst.
ΔH = 180 -200 = -20
Question 7
1 / -0

Hydrolysis of DDT is a first order reaction. Its half-life is 10 year. Time to hydrolyse 10 g DDT to half of its original amount is

A
100 year

B
50 year

C
5 year

D
10 year

Solution
Question 8
1 / -0

The rate constant of a first order reaction is 3 * 10^-6 per second and initial concentration is 0.10 M. The initial rate of reaction is

A
3 * 10^-6 Ms^-1

B
3 * 10^-8 Ms^-1

C
3 * 10^-7 Ms^-1

D
3 * 10^-9 Ms^-1

Solution

Rate = K[A]¹
= 3 x 10^-6 x 0.1 = 3 x 10^-7 Ms^-1
Question 9
1 / -0

For the reaction Cl₂ + 2I^-⇒ I₂ + 2Cl^-, the initial concentration of I- was 0.20 mol L^-1 and the concentration after 20 min was 0.18 mol L^-1. The rate of formation of I2 in mol lit^-1 would be

A
1 * 10^-3

B
5 * 10^-4

C
1 * 10^-4

D
2 * 10^-3

Solution
Question 10
1 / -0

Which of the following does not express the reaction rate for the above reaction?

A

B

C

D

Solution
Question 11
1 / -0

Directions: The following question has four choices out of which ONLY ONE is correct.
The method usually employed for dispersion of a colloidal solution is

A
addition of electrolytes

B
diffusion through animal membrane

C
condensation

D
dialysis

Solution

Peptization - Some freshly prepared precipitates, such as AgCl, Fe (OH)₃ and Al(OH)₃, can be converted into colloidal solutions by addition of small amount of suitable electrolyte. An electrolyte having an ion common with material to be dispersed is required for sol formation.
For example, the ferric hydroxide sol is obtained when small amount of ferric chloride solution is added. Similarly, Al(OH)₃ sol is obtained when small amount of hydrochloric acid is added to freshly precipitated Al(OH)₃.
Question 12
1 / -0

Coagulation of lyophobic colloids can be carried out by

A
boiling

B
persistent dialysis

C
electrophoresis

D
All of the above

Solution

The phenomenon of precipitation of a colloidal solution by the addition of excess of an electrolyte is called coagulation or flocculation.
The coagulation of lyophobic colloids can be carried out by the following methods:
(1) By electrophoresis: In electrophoresis, the colloidal particles move towards oppositely charged electrode. When these come in contact with the electrode for long, these are discharged and precipitated.
(2) By mixing two oppositely charged sols: When oppositely charged sols are mixed in almost equal proportions, their charges are neutralised. Both sols may be partially or completely precipitated as the mixing of ferric hydroxide (+ve sol) and arsenious sulphide (–ve sol) brings them in precipitated form. This type of coagulation is called mutual coagulation or meteral coagulation.
(3) By boiling: When a sol is boiled, the adsorbed layer is disturbed due to increased collisions with the molecules of dispersion medium. This reduces the charge on the particles and ultimately they settle down to form a precipitate.
(4) By persistent dialysis: On prolonged dialysis, the traces of electrolyte present in the sol are removed almost completely and the colloids become unstable.
Question 13
1 / -0

Directions: The following question has four choices out of which ONLY ONE is correct.
Which of the following statements is not correct?

A
Adsorption energy for chemical adsorption is generally greater than that for physical adsorption.

B
Physical adsorption is due to van der Waals forces.

C
Physical adsorption decreases at high temperature.

D
Physical adsorption is an irreversible reaction.

Solution

Physical adsorption can be reversed by increasing the temperature. So, it is a reversible process.
Question 14
1 / -0

In adsorption, rate of physisorption increases when

A
temperature is decreased

B
temperature is increased

C
pressure is decreased

D
None of these

Solution

The rate of physical adsorption increases on decreasing the temperature and the rate decreases on increasing the temperature.
Question 15
1 / -0

A colloidal phase in which gas bubbles are dispersed in a liquid phase is known as

A
foam

B
sol

C
aerosol

D
emulsion

Solution

A foam is a colloidal system in which gas bubbles are dispersed in a liquid or solid. Although the diameters of the bubbles usually exceed 10⁴Å, the distance between the bubbles is usually less than 10⁴Å, so foam is classified as colloidal system.