3.4-6 Molar Calculations

1. Molar calculations review

1. 6.02 x 10²³ particles = 1 mole
2. [molar mass] g = 1 mole
1. molar mass is the sum of atomic masses
3. Reaction coefficients can be interpreted as moles or particles.

Ex VIDEO

When the ore lead (II) sulfide reacts with oxygen, the products are lead (II) oxide and sulfur dioxide gas. How many grams of oxygen are required to react with 0.125 mol of lead (II) sulfide?

2. Empirical formulas

• Lowest whole-number ratio of atoms in a compound
• The molecular (true) formula is the same or a multiple of the empirical formula.

2. Empirical formulas

C. Given mass or % composition, find relative moles of each element. Then divide by the smallest number of moles.

D. If within 0.1, round to whole number. Otherwise, multiply:

Ex VIDEO

Ascorbic acid, also known as vitamin C, is 40.9% carbon, 4.58% hydrogen, & 54.5% oxygen by mass. If the molar mass is 176 g, what are the empirical and molecular formulas?

3. Combustion Analysis

1. CO₂ & H₂O are collected as products.
2. Use mass of products to find mass of reactants.

Ex VIDEO

When 1.125 g of a liquid hydrocarbon, CxHy, was burned in a combustion apparatus, 3.447 g of CO₂ and 1.647 g of H₂O were produced. In a separate experiment, the molar mass of the compound was found to be 86.2 g/mol. Determine the empirical and molecular formulas for the unknown hydrocarbon.

Ex VIDEO

A hydrocarbon is composed of C, H, and O atoms. Combustion of a 0.225 g sample of this compound produces 0.512 g CO₂ and 0.209 g H₂O. What is the empirical formula? If the molar mass is 116 g/mol, what is the molecular formula?