Chemistry Test 23

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Chemistry Test 23

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Weekly Quiz Competition

Question 1
4 / -1

The reason for double helical structure of DNA is operation of

A
van der Waals’ forces

B
dipole-dipole interaction

C
hydrogen bonding

D
electrostatic attractions

Solution

Hydrogen bonding is involved molecular force in the DNA molecule. Watson and Crick observed the purine-pyrimidine type of hydrogen bonding (instead of purine-purine and pyridine-pyridine).
Hence, option C is correct.
Question 2
4 / -1

The decreasing values of bond angles from NH₃ (106 °) to SbH₃ (101 °) down group-15 of the periodic table is due to

A
decreasing 1p – bp repulsion

B
increasing electronegativity

C
increasing bp – bp repulsion

D
increasing p-orbital character in sp³

Solution

The bond angle decreases from tetrahedral angle of 109 °28′ to 107 ° in NH₃ because lp – bp repulsion. On moving form NH₃ to SbH₃, the electronegativity of the central atom decreases, so, bp – bp repulsion decreases and hence bond angle decreases.

Decrease in bond angle is also caused due to increase in p-character of the hybrid (sp³) orbital. In SbH₃ the bond angle decreases to almost 101 ° indicating that pure p-orbitals are involved in bonding.
Question 3
4 / -1

The time for half-life period of a certain reaction A → Products is 1 hour, when the initial concentration of the reactant ‘A’ is 2.0 mol L^–1, how much time does it take for its concentration to come from 0.50 to 0.25 mol L^–1 if it is a zero order reaction?

A
1 h

B
4 h

C
0.5 h

D
0.25 h

Solution

In case of zero order reaction rate of reaction remains constant irrespective of change in concentration of reactant. Since it took one hour for the decrement of 1M concentration of reactant So, the time elapsed in 0.25 M change in concentration of reactant is 0.25 hour.
Question 4
4 / -1

Which of the following oxides is amphoteric in character?

A
CaO

B
CO₂

C
SiO₂

D
SnO₂

Solution

CaO → basic
SiO₂ & CO₂ → acidic
SnO₂→ amphoteric
Hence, option D is correct.
Question 5
4 / -1

The radius of Li³⁺ (Atomic number of La = 57) is 1.06 Å. Which one of the following given values will be closest to the radius of Lu³⁺ (Atomic number of Lu = 71)?

A
1.60Å

B
1.40Å

C
1.06Å

D
0.85Å

Solution

Due to lanthanide contraction there occurs net decrease in size.
Only one 0.85 Å is smaller one.
Hence, option D is correct.

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Chemistry Test 23

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Chemistry Test 23

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SHARING IS CARING

Question 1

van der Waals’ forces

dipole-dipole interaction

hydrogen bonding

electrostatic attractions

Solution

Question 2

decreasing 1p – bp repulsion

increasing electronegativity

increasing bp – bp repulsion

increasing p-orbital character in sp3

Solution

Question 3

1 h

4 h

0.5 h

0.25 h

Solution

Question 4

CaO

CO2

SiO2

SnO2

Solution

Question 5

1.60Å

1.40Å

1.06Å

0.85Å

Solution

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increasing p-orbital character in sp³

CO₂

SiO₂

SnO₂