Question

When Kay added 30 g of hydrochloric acid (HCl) to 65 g of Zn, bubbles appeared and a white precipitate, zinc chloride (ZnCl2) was produced. She found that the mass of the zinc chloride was 63 g. Since the Law of Conservation of Matter stated that matter can't be created or destroyed, she was puzzled about the difference in mass. What is the best explanation for the missing 2 g?
A) 2 g of zinc disappeared.
B) 2 g of hydrogen gas were produced.
C) Kay didn't correctly mass the precipitate.
D) Kay didn't collect all of the precipitate.

Answer 1

B) 2g of hydrogen gas were produced...

Answer 2

Hello!

The best explanation for the missing 2 g is that B) 2 g of hydrogen gas were produced.

Why?

The reaction between Hydrochloric acid (HCl) and Zn is the following one:

2HCl(aq) + Zn(s) → ZnCl₂(s) + H₂(g)

In this reaction, we can see that Hydrogen gas (H₂) is produced as well as Zinc chloride.

If the container was open to the environment, the gaseous H₂ that is produced in the reaction is lost and the mass that Kay records is only the mass of the Zinc Chloride.

Have a nice day!