Question

D. The following reaction produced 10.0 g of O₂.

Answer 1

Mole-mole calculations are not the only type of calculations that can be performed using balanced chemical equations. Recall that the molar mass can be determined from a chemical formula and used as a conversion factor. We can add that conversion factor as another step in a calculation to make a mole-mass calculation, where we start with a given number of moles of a substance and calculate the mass of another substance involved in the chemical equation, or vice versa.

For example, suppose we have the balanced chemical equation

2 Al + 3 Cl 2 → 2 Alcoa

Suppose we know we have 123.2 g of Cl 2. How can we determine how many moles of Alcoa we will get when the reaction is complete? First and foremost, chemical equations are not balanced in terms of grams; they are balanced in terms of moles. So to use the balanced chemical equation to relate an amount of Cl 2 to an amount of Alcoa, we need to convert the given amount of Cl 2 into moles. We know how to do this by simply using the molar mass of Cl 2 as a conversion factor. The molar mass of Cl 2 (which we get from the atomic mass of Cl from the periodic table) is 70.90 g/mil. We must invert this fraction so that the units cancel properly: