Chemistry Test 187

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Chemistry Test 187

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Weekly Quiz Competition

Question 1
4 / -1

Sodium and potassium react with water much more vigorously than lithium because :

A
sodium and potassium have high values of hydration energy as compared to that of lithium.

B
sodium and potassium have higher melting point than that of lithium.

C
sodium and potassium have lower melting point than that of lithium.

D
sodium and potassium have lower hydration energy than that of lithium.

Solution

When sodium and potassium react with water, the heat evolved causes them to melt, giving a larger area of contact with water, lithium on the other hand, does not melt under these condition and thus reacts more slowly.
Question 2
4 / -1

On dissolving moderate amount of sodium metal in liquid NH₃ at low temperature, which one of the folloiwng does not occur ?

A
Blue coloured solution is obtained.

B
Solvated Na⁺ ions are formed in the solution

C
Lilquid NH₃ becomes good conductor of electricity

D
Liquid NH₃ remains diamagnetic

Solution

liquid NH₃ solution is paramagnetic due to the presence of solvated unpaired electrons.
Question 3
4 / -1

KO₂ (potassium super oxide) is used in space and submarines because it :

A
absorbs CO₂ and increases O₂ contents

B
eliminates moisture and increases CO contents

C
absorbs CO₂ only

D
produces ozone

Solution
Question 4
4 / -1

Which of the following statements is incorrrect ?

A
The superoxide ion (i.e., O₂^–) is stable only in presence of larger cations such as K, Rb, Cs.

B
Alkali metals are normally kept in kerosene oil.

C
All the alkali metal hydrides are ionic solids with high melting points.

D
The concentrated solution of alkali metals in liquid ammonia are paramagnetic in nature.

Solution

(A) Bigger anion is stabilised by bigger cation through lattice energy effect.

(B) Because of their high reactivity towards air and water.

(C) True Statement

(D) In concentrated solution, unpaired electrons with opposite spins paired up-forming the solution diamagnetic.
Question 5
4 / -1

On commercial scale, sodium hydroxide is prepared by which one of the following methods ?

A
Dow's process

B
Solvay process

C
Castner-Kellner cell

D
Hall-Heroult process

Solution

(A) Used for extraction of Mg from sea water.

(B) Used for the manufacture of Na₂CO₃ using NaCl as raw material.

(C) Used for manufacture of NaOH by electrolysis of brine(concentrated NaCl solution).

(D) Used for the extraction of aluminium from bauxite.
Question 6
4 / -1

A metal (M) burns with dazzling brilliance in air to give a white powder. The white powder reacts with water to form a white precipitate and a colourless gas with a characteristic smell. The metal (M) decomposes hot water but not cold water, liberating the inflammable hydrogen gas. The metal(M) is :

A
K

B
Ca

C
Mg

D
Rb

Solution

Hydrogen is liberated when Mg reacts with hot water. Rb, K and Ca gives hydrogen gas even with cold water.
Question 7
4 / -1

On the addition of mineral acid to an aqueous solution of borax, the compound formed is:

A
borodihydride

B
orthoboric acid

C
metaboric acid

D
pyroboric acid

Solution

Na₂B₄O₇ + H₂SO₄ + 5H₂O → Na₂SO₄ + 4H₃BO₃ (orthoboric acid)
Question 8
4 / -1

B³⁺ cannot exist in aqueous solution becuase of its :

A
strong reducing ability

B
strong oxidizing ability

C
small size and large charge

D
large size and small charge

Solution

Being covalent in nature because of small size and large charge it gets hydrolysed in aqueous solution according to the following reaction
Question 9
4 / -1

The decrease stability of higher oxidation state in p-block with increasing atomic number is due to :

A
the reluctance of electrons of s-sub shell to participate in chemical bonding

B
increase in bond energy on going down the group

C
poor screening effect of d-orbitals

D
none of the above

Solution

The inert pair effect is the tendency of the electrons in the outermost atomic s orbital to remain unionized or unshared in compounds of post-transition metals. Down the group in the p-block, the inert pair effect becomes more pronounced on account of enhanced increase in effective nuclear charge. Therefore, due to reluctance of electrons of s-subshell to participate in chemical bonding, there occurs a decrease in stability of higher oxidation states in p-block with increasing atomic number.
Question 10
4 / -1

The structural unit present in pyrosillicates is :

A

B

C

D

Solution

In pyrosilicate, one oxygen atom is shared between two SiO₄^4- tetrahedra.