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Sunday, September 22, 2013

CBSE Board Important Question For SA_1-2014



10th Chemistry Some Important CBSE BOARD Question solution

Q. An aluminium can is used to store ferrous sulphate solution. It is observed that in a few days

holes appeared in the can. Explain the cause for this observation and write chemical equation to support your answer

Ans: Reactivity of aluminium is far mor than iron(Fe). Because of high reactivity aluminium displaces iron from its sulphate solution and made its sulphate sulution i.e. , aluminium sulphate. and thats why holes appeared.

2Al + 3FeSO4 = Al2(SO4)3 +3 Fe

Q. What do you mean by the term hydrated salt? Give two examples of hydrated salts which are white and state their chemical formula. Why is tooth paste used for cleaning teeth?

Ans: Hydrated salts are those salts which contains some water of crystallization.

For example: MgSO4.7H2O,SnCl2.2H2O

When we wake up at morning our mouth contains sliva of pH=4.1(acidic) due to presence of more lactic acid, which can decay our teeth so we use toothpaste which contains some alkaline compound which neutralizes the acidity of our mouth and protect from decaiying of teeth.

Q.Why do we store silver chloride in dark bottles?

An: we store silver chloride in dark bottles because of to prevent them from direct sunlight .when silver chloride is exposed to light , it decomposes to form silver metal chlorine gas .

2AgCl ----> 2Ag +Cl2

Q. What Happens When Chlorine Is Passed Over dry Slaked Lime? Write The chemical equation involved in the reaction. mention Three properties Of The Product?

Ans: When chlorine is passed through dry slaked lime power Ca(OH)2 , bleaching powder is obtained .

Ca(OH)2 + Cl2 ------> CaOCl2 + H2O

CaOCl2 is bleaching powder

The three properties Of bleaching powder , (CaOCl2) are

It is a yellowish white powder with a strong smell of chlorine

It reacts with carbon dioxide , dil. HCl and di. H2SO4 to form chlorine gas.

It is soluble in water but since it is generally contaminated with Ca(OH)2 , it may produce a milky solution.

Q. why zinc is used in the galvanization of iron and not the copper?

Ans: Zinc is more reactive than iron, it is used to protect it from corrosion because when oxygen in the air reacts with the surface of zinc, a very dense and impermeable coating of zinc oxide is formed and it is this physical barrier that protects the zinc surface from further attack.

Copper is a less reactive metal and it is difficult to form alloys with iron and go on a separate layer. Therefore it is not used for galvanization.

Q. why does the colour of copper sulphate crystals change on heating ?

Answer: The colour of the compound before heating is blue, and after heating is white-grey because the water molecules are lost on heating and copper sulphate pentahydrate is converted to anhydrous copper sulphate.

CuSO4 . 5H2O ---Heat--à CuSO4 + 5H2O

1 comment:

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