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Published on: 01/08/2018
In this question paper, some of the important one mark, two and five marks questions from the chapter The p-block Elements are covered. The questions are prepared from the book back and creative question.
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Questions + Answers key
Take MCQ Chemistry Test
1.
Why is diamond a bad conductor of electricity but a good conductor of heat?
2.
Why does silicon show a higher covalency than carbon?
3.
Explain the nature of boric acid as a Lewis acid in water?
4.
What is the formula of kernite, an ore of boron?
5.
What is inert pair effect?
6.
Why does lime water turn milky when CO2 is passed through it.
7.
Explain Silicon forms SiF62- ion whereas corresponding chloro molecule is a resonance of carbon is not known.
8.
Explain why is there a phenomenal decrease in ionisation enthalpy from carbon to silicon?
9.
What is the oxidation state of carbon in each of the following:
(i) CO2
(ii) CaC2
(iii) H2CO3
(iv) HCN
(v) CO
10.
Discuss the pattern of variation in the oxidation states of B to TI
11.
Identify the compounds A, X and Z in the following reactions,
\(Z+3LiAlH_{ 4 }\rightarrow X+3LiF+3AlF_{ 3 }\)
\( X+6{ H }_{ 2 }O\rightarrow Y+6{ H }_{ 2 }\)
\(X+3O_{ 2 }\underrightarrow { \Delta } B_{ 2 }O_{ 3 }+3{ H }_{ 2 }O\)
12.
Explain CO is heated with ZnO
13.
Explain Silicon is heated with methyl chloride at high temperature in the presence of copper.
14.
Explain the Aluminium alloys are used to make aircraft body.
15.
Classify the following oxides as neutral acidic, basic or amphotrric
CO, B2O3, Sio2, CO2, Al2O3, PbO2, Tl2O3
16.
Elemental silicon does not form a graphite-like structure as carbon does.Given reason.
17.
What happens when BF3 is reacted with ammonia?
18.
What happens when borax is heated strongly?
1.
( )
Conduction of electricity essentially requires movement of electrons while conduction of heat does not necessarily require movement of electrons.
2.
( )
Si because of the presence of vacant d-orbitals can show a covalency upto six while C because of the absence of d-orbitals cannot have a covalency of more than four.
3.
( )
It is not a protic acid because it does not ionise in H2 O to give a proton. It acts as a Lewis acis by accepting electrons from a hydroxyl ion of water and in turn releases H+ ions.
B(OH)3 + HOH\(\longrightarrow \)[B(OH)4]- + H+
4.
( )
Formula of kernite, Na2[B4O5(OH)4] or Na2B4O7 .2H2O
5.
( )
In the elements of 4th, 5th and 6th period of the p-block the electrons present in the intervening d and f-orbitals do not shield the s-electrons of the valence shell effectively. As a result, ns-2-electrons remain more tightly held by the nucles and hence, do not participate in bonding, this is called inert pair effect.
6.
When carbon dioxide is passed through lime water it turn milky due to the formation of CaCO3.
But when carbon dioxide is passed continuously, the milkiness disappears due to the formation of soluble Ca(HCO3)2.
Ca(OH)2 + CO2\(\longrightarrow \)CaCO3 + H2O
Milkiness
CO2/H2O \(\longrightarrow \)Ca(HCO3)2
Soluble in water
7.
In silicon, vacant 3d orbitals are available due to which it can accomodate electrons from six fluorine atoms, there by forming [SiF6]2- ion.However in case of C only 2p2 filled orbitals are available thus, it cannot expand their covalency more than 4. That why.[CF6]2- is not known.
8.
As we move from carbon to silicon atomic size increases, i.e. the distance between the outermost electron and nucleus increases. Thus, this electron experience very small attraction from the nucleus and hence, easy to remove. Since, the size of Si-atom is larger, the outer electron experience lesser attraction and hence, its ionisation enthalpy (energy required to remove ab electron) is smaller.
9.
| Carbon compounds | oxidation state | |
| (i) | CO2 | +4 |
| (ii) | CaC2 | -1 |
| (iii) | H2CO3 | +4 |
| (iv) | HCN | +2 |
| (v) | CO | +2 |
10.
| Element | B | AI | Ga | In | Tl |
| Oxidation state | +3 | +3 | +3,+1 | +3,+1 | +1 |
Boron and aliminium show an oxidation state of +3 only because they do not exhibit insert pair effect due to the absence of d or f-electrons. Elements from Ga to TI show two oxidation states, i.e +1 and +3.The tendency to show +1 oxidation state increases down the group due to the inability of ns2 electrons of valence shell to participate in bonding which is called inert pair effect. Therefore TI+ is more stable than TI3+
11.
\(4BF_{ 3 }+3LiAlH_{ 4 }\rightarrow 2B_{ 2 }H_{ 6 }+3LiF+3AlF_{ 3 }\)
Boron trifluride(Z) Diborane(X)
\(B_{ 2 }H_{ 6 }+6H_{ 2 }O\rightarrow 2H_{ 3 }BO_{ 3 }+6H_{ 2 }\)
(X) Orthoboric acid(Y)
\(B_{ 2 }H_{ 6 }+3O_{ 2 }\underrightarrow { \Delta } B_{ 2 }O_{ 3 }+3{ H }_{ 2 }O\)
(X)
12.
CO is strong reducing agent but it cannot reduce ZnO and get converted into CO2\(\triangle \)rGo for conversion is always higher than that of formation of ZnO. Thus, no reaction takes place.
13.
When Si is heated with CH3Cl at high temperature in the presence of Cu as a catalyst, a mixture of mono, di and trimethylchlorosilane along with a small amount of tetramethylsilane is formed.
CH3Cl + Si \(\underrightarrow { Cu \ powder } \) CH3SiCl3 + (CH3)2SiCl2 + (CH3)3SiCl + (CH3)4Si
570K
14.
Aluminium alloys such as duralumin is light, tough and resistant to corrosion and hence, it is used in making aircraft body.
15.
Neutral oxides: CO;
Acidic oxides: B2O3, SiO2 and CO2
Basic oxide : Tl2O3
Amphoteric oxides: Al2O3 and PbO2
16.
Silicon does not form \({ p\pi -p\pi }\) multiple bonds because of large size of silicon atom Hence, silicon does not form graphite-like structure as carbon does.
17.
BF3 being a Lewis acid accepts a pair of electrons from NH3 to form the corresponding complex.
F3B NH3\(\rightarrow\) F3B\(\leftarrow\)NH3
Lewis acid Lewis base Complex
18.
When borax is heated strongly, a transparent glassy bead which consists of sodium metaborate and boric anhydride is formed.
Na2B4O7.10H2O\(\overset { heat}{ \rightarrow } \)Na2B4O7 + 10H2O
Anhydrous (swollen white mass)
Na2B4O7\(\overset { heat }{ \rightarrow } \)\(\underbrace { 2Na{ BO }_{ 2 }\quad \quad \quad \quad \quad \quad \quad \quad +\quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad { B }_{ 2 }{ O }_{ 3 }\\ Sodium\quad metaborate \ Boric \ anhydride }_{ Transparent \ glassy \ bead } \)
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