2 Marks Questions

Question 12 Marks

Explain why $NH _3$ is basic while $BiH _3$ is only feebly basic?

Answer

$NH _3$ is basic while $BiH _3$ is only feebly basic because the intensity of charge on $NH _3$ due to its small size is very high, the large electron density on central atom can easily donate its lone pair of electron and acts as Lewis base.
In case of $BiH _3$ due to larger size the electron density around central atom is less. So, it behaves as mild base because it does not donate its lone pair easily.

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Question 22 Marks

Complete the following reaction :
(i) $\quad KBr + Cl _2 \longrightarrow \ldots \ldots+\ldots \ldots$.
(ii) $I _2+ H _2 O + Cl _2 \longrightarrow \ldots \ldots .+\ldots \ldots .$.
(iii) $\quad NaOH + Cl _2 \longrightarrow \ldots \ldots+\ldots \ldots$
(Cold and dilute)

Answer

(i) $2 KBr + Cl _2 \longrightarrow 2 KCl + Br _2$
(ii) $I _2+6 H _2 O +5 Cl _2 \longrightarrow 2 HIO _3+10 HCl$
(iii) $\quad 2 NaOH + Cl _2 \longrightarrow NaCl + NaOCl + H _2 O$
(Cold and dilute)

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Question 32 Marks

$SiF _6^{2-}$ is known but $SiCl _6^{2-}$ is not, why?

Answer

Due to smaller size of F as compared to Cl , steric repulsions will be less in $SiF _6^{2-}$ than in $SiCl _6^{2-}$. Because of smaller $S - F$ bond as compared to $S - Cl$ bond, the interaction of F lone pair of electrons with Si is stronger than that of Cl lone pairs.

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Question 42 Marks

Answer the following :
(a) Sulphurous acid is a reducing agent.
(b) Fluorine forms only one oxoacid.
(c) Boiling point of noble gases increases from He to Rn.

Answer

(a) Because sulphur readily gets oxidized itself to more stable +6 state.
(b) Because of absence of $d$-orbital in fluorine.
(c) From He to Rn, size increases and there is increase in Vandor Wall force.

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Question 52 Marks

Complete the following chemical reactions :
(a) $MnO _2+4 HCl \longrightarrow$
(b) $XeF _6+ KF \longrightarrow$
(c) $I ^{-}( aq )+ H ^{+}( aq )+ O _2(g) \longrightarrow$

Answer

(a) $MnO _2+4 HCl \longrightarrow MnCl _2+ Cl _2+2 H _2 O$
(b) $\quad XeF _6+ KF \longrightarrow K ^{+}\left[ XeF _7\right]^{-}$
(c) $4 I _{( aq )}^{-}+4 H _{( aq )}^{+}+ IO _2(g) \longrightarrow 2 I _{2(s)}+2 H _2 O _{(l)}$

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Question 62 Marks

Write balanced chemical equations for the following processes :
(i) $XeF _2$ undergoes hydrolysis.
(ii) $MnO _2$ is heated with conc. HCl .

Answer

(i) $XeF _2$ is soluble in water and undergoes hydrolysis to produce Xe metal and $O _2$ gas.
$2 XeF _2+2 H _2 O \rightarrow 2 Xe +4 HF + O _2$
(ii) $MnO _2$ reacts with concentrated HCl to produce manganese chloride, water and chlorine gas.
$MnO _2+4 HCl \rightarrow MnCl _2+ H _2 O +2 Cl _2$

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Question 72 Marks

HI is stronger acid than HF. Explain.

Answer

This is due to the fact that the bond strength (or bond dissociation energy) of H-I bond is minimum and that of HCl is maximum and hence HI is capable of giving I ions very easily. Thus the tendency to donate the electron pair (nucleophilicity) to carbon of halide decreases in the order $ I^{-} > Br^{-} > Cl^{-} $, the order of reactivity of halogen acids decreases in the same order $ HI > HBr > HCl $.

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Question 82 Marks

Why oxygen is a gas while sulphur is a solid?

Answer

Oxygen due to its small size and high electronegativity forms $\pi-\pi$ double bond and the intermolecular forces of attraction between oxygen molecules are weak Vander Waals forces so it is gas at room temperature.
Sulphur do not for $\pi-\pi$ multiple bond due to its larger size. It has complex structure. It exists as octa-atomic molecule.

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Question 92 Marks

Halogens are strong oxidising agents. Why?

Answer

The electron affinity of halogens is maximum among all the groups. Higher is electron affinity, more is the tendency to gain electron and thus more is the tendency to get itself reduced and more is oxidizing power.
$ X + e \rightarrow X^{-} $
$ \Delta H = -EA $ (higher values)

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Question 102 Marks

Complete the following :
(i) $NaBr + H _2 SO _4 \xrightarrow[ MnO _2]{\Delta}$
(ii) $I _2+ Na _2 S_2 O _3 \longrightarrow$

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Question 112 Marks

Why do noble gases have comparatively large atomic sizes?

Answer

The atomic radii of noble gases are by far the largest in their respective periods. This is due to the reason that noble gases (because they do not form molecules) have only vander Waals radii while others have covalent radii. As we move down the group at the atomic radii further increase is primarily due to increase in the number of shells.

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