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 93 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

Answer:

B) 2 g of hydrogen gas were produced.

Explanation:

Metals and acids react to form a salt and hydrogen gas, so this is the most likely explanation.

Answer 2

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

Explanation:

According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

$Zn(s)+2HCl(aq)\rightarrow ZnCl_2(s)+H_2(g)$

Given: mass of reactants = mass of zinc + mass of  hydrochloric acid  = 65 g + 30 g = 95 g

Mass of products = Mass of zinc chloride + mass of hydrogen

As we know , mass of reactants = mass  of products

Mass of zinc chloride + mass of hydrogen  = 95 g

Given : Mass of zinc chloride = 93 g

93 g + mass of hydrogen  = 95 g

mass of hydrogen  = 95 g - 93 g = 2 g

Thus 2 g of hydrogen gas were produced.