Question

Ms. Block's students are studying chemical reactions. A classic reaction occurs when a metal is added to hydrochloric acid. Miguel and Kai added 30g of hydrochloric acid (HCl) to 30g of magnesium (Mg) in a large test tube; bubbles appeared, the test tube felt warm, and they could no longer see the magnesium. They found that the mass of the products of the reaction was 52g. Since the Law of Conservation of Matter stated that matter cannot be created or destroyed, they was puzzled about the difference in mass. What is the best explanation for the missing 8g?

Answer 1

The boys should cover the end of the test tube to a ballon

Answer 2

Answer: The missing mass of 8 grams was of hydrogen.

Explanation:

Law of conservation of mass states that mass can neither be created nor be destroyed but it can only be transformed from one form to another form.

This also means that total mass on the reactant side must be equal to the total mass on the product side.

The chemical equation for the reaction of magnesium metal and hydrochloric acid follows:

$Mg+2HCl\rightarrow MgCl_2+H_2$

Let the mass of hydrogen gas be 'x' grams

We are given:

Mass of hydrochloric acid = 30 grams

Mass of magnesium metal = 30 grams

Mass of magnesium chloride = 52 grams

Total mass on reactant side = 30 + 30 = 60 g

Total mass on product side = 52 + x  

So, by applying law of conservation of mass, we get:

$60=52+x\\\\x=(60-52)g=8g$

The missing mass of 8 grams was the mass of hydrogen gas which was also formed in the reaction but got disappeared in the air.

Hence, the missing mass of 8 grams was of hydrogen.