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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$:$
$100-74.2=25.8%$

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

The formula for % composition of a compound is:

  1. molar mass of a compound/mass due to specific component $\times$ 100
  2. mass due to specific component $\times$ 100
  3. mass due to specific component/molar mass of a compound $\times$ 100
  4. molar mass of a specific component/temperature $\times$ 100
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

To calculate the per cent composition of a component in a compound: Find the molar mass of the compound by adding up the masses of each atom in the compound using the periodic table or a molecular mass calculator. Calculate the mass due to the component in the compound you are for which you are solving by adding up the mass of these atoms. Divide the mass due to the component by the total molar mass of the compound and multiply by 100.

% $\text{composition of a compound}=\cfrac{\text{ Mass due to specific component}}{\text{molar mass of a compound}}\times 100$

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

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

% composition requires ................ of the compound :

  1. molar mass

  2. temperature

  3. atmospheric pressure

  4. both a and b
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The present composition (by mass) of a compound can be calculated by dividing the mass of each element by the total mass of the compound. i.e. by calculating the $molar$ $mass$ of the compound.

Multiple choice chemistry d- and f-block elements comparison of lanthanoids and actinoids actinoids the actinoids

More number of oxidation states are exhibited by the actinoids than by lanthanoids. The main reason for this is:

  1. greater metallic character of the lanthanoids than that of the corresponding actinoids.

  2. more active nature of the actinoids.
  3. more energy difference $5f$ and $6d$-orbitals than that between $4f$ and $5d$-orbitals.
  4. lesser energy difference between $5f$ and $6d$-orbitals than that between $4f$ and $5d$-orbitals.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Actinoids display more oxidation states because of very small energy gap between 5f, 6d and 7s sub shells. Thus, the outermost electrons get easily excited to the  higher energy level giving variable oxidation state.

Hence,option D is correct.