Tag: percentage composition and empirical formula

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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.

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

Potash alum contains ___________ number of water molecules.

  1. 24

  2. 22

  3. 20

  4. 25
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Potash Alum $(K _2SO _4 Al _2 (SO _4) _3 .24H _2O)$ is a colourless, odourless and crystalline substance. Its crystals are prepared by mixing concentrated solutions of potassium sulphate and aluminium sulphate. It is soluble in water. It contains 24 molecules of water.

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

Copper sulphate pentahydrate is commonly called as____, whereas ferrous sulphate heptahydrate is commonly called as _____ .

  1. white vitriol, blue vitriol

  2. green vitriol, blue vitriol

  3. blue vitriol, green vitriol

  4. blue vitriol, white vitriol
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Copper sulphate pentahydrate ($CuSO _4.5H _2O$) commonly known as blue vitrol contains 5 water molecules which gives it a blue color. Similarly, the green color of ferrous sulphate heptahydrate ($FeSO _4.7H _2O$) is due to 7 molecules water present in it. This water is responsible for the geometric shape and color of the crystals.

Multiple choice chemistry introduction to analytical chemistry percent composition water of crystallisation percentage composition and empirical formula

Compound Q contains $40\%$ carbon by mass.
What could Q be?
$1$. glucose, $C _6H _{12}O _6$
$2$. starch, $(C _6H _{10}O _5) _n$
$3$. sucrose, $C _{12}H _{22}O _{11}$.

  1. $1, 2$ and $3$ are correct
  2. $1$ and $2$ only are correct
  3. $2$ and $3$ only are correct
  4. $1$ only is correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
$\text{percentage mass of C}=\dfrac{\text{mass of C X 100%}}{\text{total mass}}$

$\text{1. percentage of C in glucose=40%}$
$\text{2. percentage of C in starch=44%}$
$\text{3. percentage of C in sucrose=42%}$
Multiple choice chemistry introduction to analytical chemistry percent composition water of crystallisation percentage composition and empirical formula

What is % composition of a substance?

  1. Sum of all the components.

  2. % composition of the sum of two components.

  3. % of the total mass of a substance.

  4. None of the above.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component.

Multiple choice chemistry introduction to analytical chemistry percent composition water of crystallisation percentage composition and empirical formula

What is the percent of composition of the compound that forms when $222.7g$ of N combines compleletly with $77.4g$ of O?

  1. $70%, 30%$
  2. $80%, 20%$
  3. $74.2%, 25.8%$
  4. $72.2%, 27.8%$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The mass composition$:$
Total mass$: 222.7+77.4=300.1$
Mass percentage of N$:$
$222.7300.1=74.25$
Mass percentage of O$:$
$100-74.2=25.8%$