Question

Chemical make-up of one of chloroform
\[\begin{matrix}
   Element & Number\text{ of moles} & Mass\text{ }per\text{ }mole(grams) \\
   Carbon & 1 & 12.011 \\
   Hydrogen & 1 & 1.008 \\
   Chlorine & 3 & 35.453 \\
\end{matrix}\]
A chemical solvent is a substance that dissolves another to form a solution. For example, water is a solvent for sugar. Unfortunately, many chemical solvents are hazardous to the environment. One eco-friendly chemical solvent is chloroform, also known as trichloromethane ($CHC{{l}_{3}}$). The table above shows the chemical makeup of one mole of chloroform.
If a chemist starts with 1000 grams of chloroform and uses 522.5 grams, how many moles of chlorine are left?

Answer 1

Hint: For a molecule, the Avogadro number is equal to molecular weight in grams. Thus, by dividing the given mass by the molar mass of the given compound we can get the number of moles in the remaining amount of sample.

Complete Solution :
- As we know, a major property of Avogadro’s number ($6.023\times {{10}^{23}}$) is that the substance’s molecular weight is equal to the mass of one mole of a substance. Similarly, the gram molecular mass of a compound refers to the mass of a single mole of the compound and the gram atomic mass of an element is the mass of one mole of that element.
- Thus, by the above mentioned relation between molar mass and we could find the number of moles in a given sample by the following equation
\[Number\text{ }of\text{ }moles~~=\dfrac{Given\text{ }mass~~}{Molar\text{ }mass}~~\]

- In the question it’s given as the chemist starts with 1000 grams and uses 522.5 gram. So the remaining amount of chloroform is 1000 − 522.5 = 477.5 grams.
The molar mass of chloroform ($CHC{{l}_{3}}$) = 119.5${g}/{mol}\;$

- Therefore the number of moles of chloroform left in 477.5 grams can be found as below
\[Number\text{ }of\text{ }moles\text{ }of\text{ }chloroform=\dfrac{Given\text{ Mass}}{Molar\text{ }Mass}=\dfrac{477.5g}{119.5{g}/{mol}\;}=4\text{ }moles\]

- We are asked to find the number of moles of chlorine left in 477.5 grams of chloroform. According to the given table, each mole of chloroform consists of 3 moles of chlorine. Therefore in 4 moles of chloroform left, the number of mole of chlorine left will be :

\[Moles\text{ }of\text{ }Chlorine\text{ }left=4\times 3=12\text{ }moles\]
- Thus 12 moles of chlorine will be left if a chemist starts with 1000 grams of chloroform and uses 522.5 grams.

Note: Keep in mind that the chloroform has a number of applications. Chloroform is used as solvent in the manufacturing industries, used in the production of organic compounds and is used in refrigerators and so on.