Lead Pencil contains

PbS
FeS
Pb₃O₄
Graphite

Solution

Lead pencil has graphite.

Gas A is bubbled through slaked lime when a white precipitate is formed. On prolonged bubbling the precipitate is dissolved. On heating the resultant solution, the white precipitate appears with evolution of gas B.The gases A and B respectively are

CO and CO
CO₂ and CO
CO and CO₂
CO₂ and CO₂

Solution

Which of the following attacks glass

Solution

Glass being a mixture of sodium and calcium silicates reacts with hydrofluoric acid forming sodium and calcium fluorosilicates respectively.
Na₂SiO₃ + 6HF ⟶ Na₂SiF₆ + 3H₂O
CaSiO₃ + 6HF ⟶ CaSiF₆ + 3H₂O

Lead pipes are not suitable for drinking water because

A layer of lead dioxide is deposited over pipes
Lead reacts with air to form litharge
Lead reacts with water containing air to form Pb(OH)₂
Lead forms basic lead carbonate

When vapours of SiCl₄ are passed over hot Mg, the product formed is

MgSiCl₆
SiCl₂ + MgCl₂
Si + MgCl₂
MgSi + Cl₂

Solution

SiCl₄ + 2Mg ⟶ Si + 2MgCl₂(vapours) hot.

Which one of the following statements about the zeolites is false ?

They are used as cation exchangers
They have open structure which enables them to take up small molecules
Zeolites are aluminosilicates having three dimensional network
None of the above

Which of the following has the highest calorific value ?

Coal gas
Water gas
Producer
Carbon dioxide gas

Solution

The larger the percentage of hydrogen present in a fuel, the higher will be its calorific value. Thus the calorific values of coal gas, water gas and producer gas are of the order of 500,350 and 103 BTH (British Thermal Unit) per cubic foot respectively.1 BTH = 252 calories.

To a piece of charcoal, sulphuric acid is added. Then:

there is no reaction
water gas is formed
SO₂ and CO₂ are evolved
CO and SO₂ are evolved

Solution

Charcoal is a pure form of carbon, its reaction with hotconc.H₂SO₄ is as follows :
C + 2H₂SO₄ ⟶ 2H₂O + 2SO₂ + CO₂

Unlike the other elements of its group carbon and silicon does not form MX₂ type molecules because :

energetically this is not possible
carbon undergoes catenation
it is non-metallic
carbon does not contain d-orbital

Solution

The stability of dihalides (MX₂) increases down the group. Except C and Si, the other members form dihalides.

Tetra ethyl lead is used as:

fire extinguisher
antiknock compound
pain killer
mosquito killer

Solution

Knocking (metallic sound or rattle) decreases the power and increases the wear of the engine. Knocking is more if petrol contains greater percentage of straight chain hydrocarbon. It is least in case of alkene/ branched chain HC/ aromatic HC. Tetra ethyl lead dissociates into ethyl radicals which combine with some straight chain HC and thus lowering the knocking property of fuel by forming branched chain HC.

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