Chemistry Test 219

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Chemistry Test 219

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Weekly Quiz Competition

Question 1
4 / -1

The oxidation number of Cl in Cl₂O₇ is

A
+ 3

B
+ 5

C
+ 7

D
– 7

Solution

Cl show different oxidation state as -1 to +7 due to vacant d orbital.

As oxygen is more electronegative than Cl.

Oxygen size is small hence its more electronegative and show -2 oxidation states.

2x + 7 (-2) = 0

x = +7
Question 2
4 / -1

The standard reduction potentials E°, for the half reactions are as:

A
–0.35 V

B
+0.35 V

C
+1.17 V

D
–1.17 V

Solution
Question 3
4 / -1

The binding of oxygen by haemoglobin (Hb) forming (HbO₂), is partially regulated by the concentration of H₃O + and dissolved CO₂ in blood.

Release of O₂ is favoured when there is

A
production of CO₂ during excertion

B
production of lactic acid during excertion

C
Both (a) and (b) take place

D
None of (a) and (b) takes place

Solution

During exercise muscle need energy hence consume more oxygen and produce more CO₂ and lactic acid gets accumulated as well. According to bohr's effect oxygen binding affinity is inversely proportional to CO₂ concentration and acidity. Thus favours the dissociation or release of O₂.
Question 4
4 / -1

Fuel cells are _________ that are designed to convert the energy of combustion of fuels like hydrogen, methane, methanol, etc. directly into _________.

A
Galvanic cells, electrical energy

B
Electrolytic cells, electrical energy

C
Galvanic cells, hydraulic energy

D
Galvanic cells, thermal energy

Solution

A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) directly into electrical energy through a pair of redox reactions.

Fuel cells are different from most batteries in requiring a continuous source of fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from metals and their ions or oxides that are commonly already present in the battery, except in flow batteries.

Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.
Question 5
4 / -1

Which of the following atom has been assigned only single oxidation number?

A
H

B
O

C
N

D
F

Solution

Fluorine is the most electronegative element. It can gain one electron.

Thus, Oxidation number = -1

F+ e- → F^-

Due to very high (IE), it cannot lose electrons.

(a) H^- (-1), (H⁺ (+1)

(b) O^-2 in oxide, -1 in peroxide, and +2 in OF₂

(c) +3 in N₂O₃, -3 in NH₃, +3 in HNO₂, +5 in HNO₃, + 1 in N₂O
Question 6
4 / -1

Cl₂ gas is passed into a solution containing KF, Kl and KBr, and CHCI₃ is added. There is a colour in CHCI₃ (lower) layer. It is due to

A
formation of l₂ (violet)

B
formation of Br₂ (orange)

C
formation of l₂ and Br₂ both

D
formation of F₂ (colourless)

Solution
Question 7
4 / -1

Which of the following reactions is a decomposition redox reaction?

A
P₄(s) + 3OH⁻(aq) + 3H₂O(l) → PH₃(g) + 3H₂PO2−(aq)

B
2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g)

C
N₂(g) + O₂(g) → 2NO(g)

D
Cl₂(g) + 2OH⁻(aq) → ClO⁻(aq) + Cl⁻(aq) + 4H₂O(l)

Solution

Decomposition redox reaction leads to breakdown of a compound into two or more compounds at least one of which must be in the elemental state with change in oxidation number.
Question 8
4 / -1

In each of the following equilibria, pressure is made four times after equilibrium is set up. In which case yield of the product(s) is maximum?

A

B

C

D

Solution

The effect of pressure on equilibrium yield depends on the change in number of gas moles (Δn_g) between reactants and products.

The general relationship is: yield ∝ (1 / pressure)^Δn_g

For (a) N₂O₄ ⇌ 2NO₂: Δn_g = 2 - 1 = +1 Increasing pressure 4 times decreases product yield by (1/4)⁺¹ = 1/4 times (yield decreases).

For (b) C + H₂O ⇌ CO + H₂: Δn_g = (1 + 1) - 1 = 1 (Note: C is solid, so only gases count) Increasing pressure 4 times decreases product yield by (1/4)⁺¹ = 1/4 times (yield decreases).

For (c) N₂ + 3H₂ ⇌ 2NH₃: Δn_g = 2 - (1 + 3) = 2 - 4 = -2 Increasing pressure 4 times increases product yield by (4)² = 16 times (yield greatly increases).

For (d) 2Fe + 3H₂O ⇌ Fe₂O₃ + 3H₂: Δn_g = 3 - 3 = 0 No change in number of gas moles, so pressure change has no effect on yield.

Thus, the equilibrium where Δn_g is negative and largest in magnitude (case c) shows the maximum increase in product yield with increased pressure.
Question 9
4 / -1

The passage of current through a solution of certain electrolye results in the evolution of H₂ at cathode and Cl₂ at anode. The electrolytic solution is -

A
Water

B
H₂SO₄

C
A NaCl

D
A CuCl₂

Solution

In this Cl^– will oxidise to give Cl₂ ,Na⁺ reduction potential has lower potential than water reduction polenlid so water will reduce to give H₂.
Question 10
4 / -1

The decomposition of hydrogen peroxide to form water and oxygen is an example of

A
Displacement reactions

B
Decomposition reactions

C
Disproportionation reaction

D
Combination reactions

Solution

A disproportionation reaction is a particular type of redox reaction in which a single compound is transformed into two different compounds, one being reduced and the other being oxidized.

The decomposition of hydrogen peroxide to form water and oxygen is a classic example of a disproportionation reaction.