Rajasthan Police Constable Model Paper 5

Question : 94 of 155

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Which of the following is the correct chemical formula of ‘gypsum’?

Solution:

Calcium Sulphate Dihydrate ( $CaSO_4 .2H_2O$ ) is commonly known as “Gypsum”.
When Gypsum is heated, it gets converted into Calcium Sulphate Hemihydrate ( $CaSO_4. 1/2H_2O$ ) or “Plaster of Paris (POP)”.
This is prepared by heating the gypsum which contains calcium sulfate dihydrate ( $CaSO _4.2H_2 O$ ) to a temperature of about 150 deg C.
When added water to the plaster of Paris (PoP), it will re-form into gypsum.
Some common chemical compounds with their common names are:-

ChemicalCompounds	CommonNames	ChemicalFormulas
Sodium Bicarbonate	Baking Soda	$NaHCO_3$
CalciumChlorohypoChlorit	BleachingPowder	$Ca(ClO)_2$
Sodium Hydroxide	Caustic Soda	NaOH
Sodium Carbonate	Washing Soda	$Na_2CO_3 .10 H_2O$
Carbon Dioxide	Dry Ice	$CO_2$
Copper Sulphate	Blue Vitriol	$CuSO_4$
Ferrous Sulphate	Green Vitriol	$FeSO_4$
Sulphuric Acid	Oil of vitriol	$H_2SO_4$
Calcium Oxide	Quick Lime	CaO
Calcium SulphateHemihydrate	Plaster ofPairs	( $CaSO_4 .1/2H_2O$ )
Calcium SulphateDihydrate	Gypsum	$CaSO_4 .2H_2O$
Calcium Hydroxide	Slaked Lime	$Ca(OH)_2$
Chile Saltpeter	Sodiumnitrate	$NaNO_3$
Saltpeter	Potassiumnitrate	$KNO_3$
Muriatic acid	Hydrochloricacid	HCl

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