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Practical Work

Detection of Some Gases

Test for hydrogen (H2):

Hydrogen gas is liberated when active metals such as Na, K, Mg react with dilute acids.

M + H2SO4             MSO4 + H2M + HCl            MCl + H2M=Ca, Mg, Zn, etc.

Few characteristics of this gas are as follows.

i. It is a colourless and odourless gas.

ii. When this gas is allowed to pass through a moist red or blue litmus paper, the colour of the paper does not change. This shows that hydrogen gas is neutral to litmus.

iii. A burning wooden splint, when brought near this gas, gets off and burns with a pale blue flame producing a pop sound.

2 H2 + O2          2 H2O

 

Test for oxygen (O2):

Oxygen gas is liberated on heating metal nitrates, potassium chlorate, potassium dichromate, potassium permanganate, hydrogen peroxide, barium peroxide and oxides such as HgO, PbO2, Pb3O4.

2PbO2      Δ      2 PbO + O22 HgO       Δ       2 Hg + O2

Few characteristics of this gas are as follows.

i. It is a colourless and odourless gas.

ii. When this gas is allowed to pass through a moist red or blue litmus paper, the colour of the paper does not change. This shows that oxygen gas is neutral to litmus.

iii. A burning wooden splint when brought near this gas re-lights brightly which shows that it is a supporter of combustion.

 

Test for water vapour (H2O):

Water vapour is liberated on heating salts containing water of crystallisation, metallic hydroxides and metallic hydrogen carbonates.

Na2CO3.10H2O       Δ      Na2CO3 + 10 H2OCuSO4.5H2O       Δ       CuSO4 + 5 H2O

Few characteristics of this gas are as follows.

i. It is a colourless and odourless gas.

ii. When this gas is allowed to pass through a moist red or blue litmus paper, the colour of the paper does not c…

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