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?

The mass has been lost as hydrogen gas.

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.

Mass of reactants= mass of zinc+ mass of hydrogen chloride= 65 g + 30 g= 95 g

Mass of products= mass of zinc chloride + mass of hydrogen=93 g +?

But mass of products = mass of reactants

Mass of hydrogen = (95-93)g = 2g

Thus 2 grams has been lost in the form of hydrogen gas which has escaped.