Question

The reaction of Copper with Sulphur
Mass of $Cu$ before reaction:	$3.17g$
Mass of $S$ before reaction:	$2.93g$
Mass of $CuS$ formed:	$4.78g$
Mass of unreacted $S$:	?

Copper $\left(Cu\right)$ and Sulphur $\left(S\right)$ were heated in a covered container. After the reaction was complete, the unreacted sulphur was removed. The table contains the results of the investigation. How much sulphur, in grams, failed to react with the copper?

• A. $1.2$
• B. $1.25$
• C. $1.3$
• D. $1.32$

Answer 1

The correct option is D $1.32$

According to the law of conservation of mass, “Mass can neither be created nor be destroyed but can be transformed from one form to another”. Which can be interpreted as, the mass of reactants= the mass of products.

Mass of $Cu$ before reaction $+$ mass of $S$ before reaction $=$ mass of $CuS$ formed $+$ unreacted$S$
Therefore mass of unreacted $S=3.17g+2.93g-4.78g=1.32g$