Chemistry Test 85

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Chemistry Test 85

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Weekly Quiz Competition

Question 1
4 / -1

Zinc on reaction with NaOH gives a salt (A) along with a gas (X) and (A) on reaction with a gas (Y) gives white precipitate (W). Which of the following is correct?

A
(A) is Na₄ZnO₃,(Y) is H₂ S

B
(X) is H₂,( W) is Zn (OH)₂

C
(A) is Na₂ZnO₂,(X) is O₂

D
(W) is ZnS,(X) is H₂

Solution
Question 2
4 / -1

Which of the following represents the incorrect order of property mentioned?

A
Ac³⁺> Th³⁺> Lr³⁺( ionic radii)

B

C
La³⁺> Ce³⁺< Lu³⁺ (ionic radii)

D
V³⁺>V²⁺ (stability of ions in solution)

Solution

Option (C): In Lanthanide series ionic radii of trivalent ions decreases as atomic number increases. This is known as lanthanide contraction. But the decrease is too small in comparison with atomic number. The decrease in size can be attributed to poor shielding of electrons present in 4f orbital.

Thus, La⁺³>Ce⁺³>Lu⁺³

So, option (C) is in incorrect order.

Option (A): Among actinides also there is a decrease in ionic radii due to poor shielding effect of electrons present in (n−2)f orbital. This is known as actinoid contraction.

Thus, Ac³⁺>Th³⁺>Lr³⁺

Option (B): More the oxidation number, more quickly it will get reduced, which means it is a strong oxidizing agent. The order of oxidation number in the given ions is:

V⁺⁵< Cr⁺⁶< Mn⁺⁷

Option (D): In solution, hydrates are formed and the stability of hydrates directly depends on oxidation number. More the oxidation number more is stability.

V⁺³> V⁺²

Hence, the correct option is (C).
Question 3
4 / -1

Isoelectric point is the pH at which colloidal particles:

A
Coagulate

B
Become electrically neutral

C
Can move toward either electrode

D
All of above

Solution

The H⁺ concentration at which the colloidal particles have no charge is known as the isoelectric point. At this point, the stability of colloidal particles becomes very less, and they do not move under the influence of the electric field. The sol particles at the isoelectric point do not show the electrophoresis process. Isoelectric point (pl or IEP) is the pH of a solution or dispersion at which the net charge on the molecules or colloidal particles is zero. In electrophoresis, there is no motion of the particles in an electric field at the isoelectric point. The net charge (the algebraic sum of all the charged groups present) of any amino acid, peptide or protein, will depend upon the pH of the surrounding aqueous environment. For example, alanine can have a charge of +1,0, or −1, depending on the pH of the solution in which it is dissolved.

Hence, the correct option is (D).
Question 4
4 / -1

The critical temperature of O₂ is less than H₂O because the H₂O molecules have:

A
Fewer electrons than O₂

B
Two covalent bonds

C
V-shaped structure

D
Dipole moment

Solution

The critical temperature is the temperature of a gas in its critical state, above which it cannot be liquefied by pressure alone. The critical temperature of O₂ is lesser than that of H₂O that means H₂O is liquified easily than O₂. Thus we can conclude that H2O molecules might be having more intermolecular attraction than O₂ molecules. Stronger interaction between H₂O molecules is because of the presence of a permanent dipole in it. While O₂ molecules are non-polar and thus have lesser interparticle attraction.

Hence, the correct option is (D).
Question 5
4 / -1

The oxidation number of phosphorus in P₄O₁₀ is:

A
+3

B
0

C
+5

D
+7

Solution

Structure of P₄O₁₀:

Now, we can see all the P atoms are in the same electronic environment and thus, have the same oxidation number.

Let the oxidation number of P be x.

As we know, oxidation of O atoms is -2.

Now we can calculate the oxidation number of P in P₄O₁₀ as:

4(x)+10(−2)=0

⇒4x=20

⇒x=+5

Hence, the correct option is (C).
Question 6
4 / -1

Identify the correct order of reactivity in electrophilic substitution reactions of the following compounds:

A
1 > 2 > 3 > 4

B
2 > 3 > 1 > 4

C
2 > 1 > 3 > 4

D
4 > 3 > 2 > 1

Solution

The −NO₂ group is electron withdrawing group, so it deactivates the benzene ring largely, −Cl atom is also deactivate the benzene ring but this deactivation is lower than −NO₂ group; while −CH₃ group activates the benzene ring. Hence, on the basis of activation and deactivation they have the following order of electrophilic attraction (because more activated group attracts electrophile easily).

Hence, the correct option is (C).
Question 7
4 / -1

Which among the following substances catalyses the conversion of SO₂ to SO₃ and causes classical smog?

A
Plants

B
IR radiation

C
Particulates

D
UV radiation

Solution

Particulate matter or pollutants are minute solid particles or liquid droplets in the air. Some examples are smoke and dust particles, ash, mist, etc. These result in the oxidation of sulphur dioxide to sulphur trioxide. Classical smog consists of smoke, fog and sulphur dioxide. Smoke comes under the category of particulate pollutants.

Hence, the correct option is (C).
Question 8
4 / -1

2,4-pentanedione is treated with excess of KCN in acetic acid solution and finally hydrolysed with dilute H₂SO₄ giving products only with molecular formula C₇H₁₂O₆ (dicarboxylic acids). Mark the correct statement regarding product(s) of this reaction.

A
Product mixture contains four steroisomers which on fractional crystallization gives two fraction.

B
Product mixture contains three steroisomers which on fractional crystallization gives two fraction.

C
Product of either fraction obtained after crystallization, on strong heating lactonizes to give the following compound.

D
Product of only, one fraction obtained after crystallization, on strong heating lactonizes to gives the following compound.

Solution

Cyanide ion is a strong nucleophile. It attacks carbonyl carbon. Thus when 2,4-pentadione is treated with excess KCN and dil acetic acid, two molecules of HCN are added across two carbonyl groups. This is followed by the hydrolysis of cyanide group in presence of dil sulfuric acid to form 2,4-dihydroxy-2,4-dimethyl pentane dioic acid. Crystallization, followed by heating gives the final product lactone.

Hence, the correct option is (C).
Question 9
4 / -1

Which of the following is the monomer of natural rubber?

A
CH₂ = CH₂

B
CH₂ = CHCI

C

D

Solution

Natural rubber considered as a linear polymer of isoprene and is also called a cis- 1,4 -polyisoprene. It is an addition polymer. Natural rubber is a sticky material. This disadvantage can be overcome by vulcanisation.

Hence, the correct option is (D).