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Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

The crystalline salt ${ Na } _{ 2 }{ SO } _{ 4 }.x{ H } _{ 2 }O$ on heating loses 55.9% of its mass. The formula of crystalline salt is:

  1. ${ Na } _{ 2 }{ SO } _{ 4 }.5{ H } _{ 2 }O$
  2. ${ Na } _{ 2 }{ SO } _{ 4 }.7{ H } _{ 2 }O$
  3. ${ Na } _{ 2 }{ SO } _{ 4 }.2{ H } _{ 2 }O$
  4. ${ Na } _{ 2 }{ SO } _{ 4 }.10{ H } _{ 2 }O$
  5. ${ Na } _{ 2 }{ SO } _{ 4 }.6{ H } _{ 2 }O$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Molar mass of Na2SO4 = 142. Mass of water = 18x. Total mass = 142 + 18x. Water loss = 18x / (142 + 18x) = 0.559. Solving for x gives x = 10.

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

State whether the given statement is true or false:

Water of crystallization is the water that occurs inside crystals.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Water of crystallization or water of hydration is water that occurs inside the crystals. It refers to water that is found in the crystalline framework of a metal or a salt that is not directly bonded to the metal cation.

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

In $FeSO _4$.$7H _2O$, $H _2O$ represents:

  1. molar mass

  2. molecular weight

  3. molar weight

  4. water of crystallisation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Water of crystallization or water of hydration is the water present inside the crystal. Solids are purified by the procedure called as crystallization in which after purification some pure form of water trap down inside the crystal called as water of crystallization.

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

The number of molecules of water of crystallisation present in one molecule of ferrous sulphate is_______.

  1. $5$
  2. $7$
  3. $6$
  4. $10$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When water is used in the formation of crystals knows as water of crystallization. 'OR' 

Water of crystallization is the total weight of water in a substance at a given temperature and is mostly present in a definite ratio. 
On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a brown-colored anhydrous solid. 


$FeSO _4.7H _2O$ the heptahydrate in solution (water as solvent) transforms to both heptahydrate and tetrahydrate when the temperature reaches $56.6 ^\circ C$.


Hence, option $B$ is correct.

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

The definite number of water molecules which enters into a chemical combination with the substance when the substance is crystallized from its hot saturated solution is called ________. 

  1. crystallization

  2. water of crystallization

  3. formation of water molecule

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The definite number of water molecules which enters into a chemical combination with the substance when the substance is crystallized from its hot saturated solution is called water of crystallization.

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

A salt associated with water of crystallization is known as a:

  1. acid

  2. buffer

  3. hydrate

  4. anion
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A salt associated with the water of crystallization is known as a hydrate. The structure of hydrates can be quite elaborate, because of the existence of hydrogen bonds that define polymeric structures.


Hence, the correct option is $\text{C}$

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

Water of crystallization is present in a definite :

  1. shape

  2. ratio

  3. volume

  4. size
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Water of crystallization or water of hydration or crystallization water is water that occurs inside crystals. Water is often necessary for the formation of crystals. Water of crystallization is the total weight of water in a substance at a given temperature and is mostly present in a definite (stoichiometric) ratio.

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

Heated calcium sulphate with half a water of crystallization is commonly called as :

  1. washing soda

  2. plaster of paris

  3. naushadar salt

  4. bleaching powder
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Plaster of paris which is chemically called calcium sulphate hemihydrate. Since, it is brought to use from paris, called as "plaster of paris". It is prepared by heating of gypsum at 373K. 

Multiple choice chemistry substances in common use percent composition water of crystallisation percentage composition and empirical formula

Since there are 10 water molecules in washing soda, hence it is known as:

  1. sodium bicarbonate decahydrate

  2. sodium carbonate decahydrate

  3. sodium bicarbonate nanohydrate

  4. sodium decahydrate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Washing soda is called sodium carbonate. Since, there are $10$ water molecules in washing soda, hence it is known as sodium carbonate decahydrate.