Question

In carbon disulphide $(C{S_2})$ the mass of sulphur in combination with $3.0g$ of carbon is
A.$4.0g$
B.$6.0g$
C.$64.0g$
D.$16.0g$

Answer 1

We know molar mass of $C{S_2}$ is $76g$, so think of percentage of contribution in mass of each atom in the molecule and then apply the basic concept of mass percentage and simple stoichiometry to find ratio of contribution in mass of each atom.

Complete step by step answer:
The above question is from the stoichiometric concept. Stoichiometry is the branch of chemistry that deals with the quantitative relationship of reactants and products and determines the amount of reactants needed and the amount of product formed.
First of all we will calculate the Molar mass of $C{S_2}$
Molar mass of C $= 12g$
Molar mass of S $= 32g$
Now,
Molar mass of $C{S_2} =$ molar mass of C + (molar mass of S) × 2
Molar mass of $C{S_2} =$ $12g + 32 \times 2g$
Molar mass of $C{S_2} =$ $76g$
Now in the above question we can see that C and S react to form $C{S_2}$ .So applying basic knowledge of stoichiometry,
$12g$ of C reacts with $64g$ of S to form $76g$ of $C{S_2}$
Or we can say that,
$12g$ of C forms $76g$ of $C{S_2}$
Then, $3.0g$ of C forms $= 76g \times 3g/12g$ of $C{S_2}$ $= 19g$ of $C{S_2}$
So, we can conclude that $3.0g$ of C forms $19.0g$ of $C{S_2}$
Now, we can also say
$76g$ of $C{S_2}$ has $64g$ of S
Then, $19g$ of has $= (64g \times 19g)/76g$ of S $= 16g$ of S
Thus we can conclude that $3.0g$ of C combines with $16g$ of S .
Hence option D is the correct answer.

Additional information: Stoichiometry is very helpful when it comes to finding unknown masses of compounds. In a simple reaction for example,
$X + Y \to W + Q$
If masses of X and W are known at a certain point then we can calculate what their masses will be in any other proportion because the ratio in which X is consumed and W is made will not change.

Note:
Do not forget to put the units wherever required. Calculate the Molar mass correctly. Use precision up to two decimal places for approximate value in calculation. Keep in mind the basic stoichiometric concept and unitary method.