Tag: water of crystallisation

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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.