Chapter 2, Problem 14STP

Interpretation Introduction

Interpretation: The amount of magnesium and oxygen that react to form 20.0 g of magnesium oxide should be determined.

Concept Introduction: In a chemical change, the chemical bonds present in reactants are broken to form elements that are then rearranged to form new chemical bonds resulting in the formation of products that possess different compositions than the reactants.

Answer to Problem 14STP

The amount of magnesium and oxygen react to form 20.0 g of magnesium oxide 12.0 g and 8.0 g respectively.

Explanation of Solution

Mass of Magnesium (g)	Mass of Oxygen (g)	Mass of magnesium oxide (g)
5	3.30	8.3
6.5	4.30	10.8
13.6	9.00	22.60
19.00	12.50	31.5

According to the law of conservation of mass, mass is conserved in any chemical or physical change. The mass of reactants is always equal to the mass of products during any chemical reaction.

On plotting the mass of magnesium on the x-axis and mass of magnesium oxide on the y-axis, the plot obtained is:

  

In order to determine the amount of magnesium required to form 20.0 g of magnesium oxide, the lines are drawn like this:

  

Thus, the amount of magnesium required to form 20.0 g of magnesium oxide is 12 g.

The amount of oxygen is calculated using the law of conservation of mass:

  $\begin{array}{l}{\text{mass of reactant (Mg + O}}_{\text{2}}\text{) = mass of product (MgO)}\\ \text{12 g + x g = 20 g}\\ \text{x g = 20 g - 12 g}\\ \text{x g = 8 g}\end{array}$

Thus, the amount of oxygen required to form 20.0 g of magnesium oxide is 8 g.