1. The Mathematics of Formulas and Equations
Chemistry Topic 3
The Mathematics of Formulas and Equations

2. Mass of atom is based on the mass of a Carbon-12 atom
Formula Mass – sum of the atomic masses of all the atoms present.
Gram Formula Mass – formula mass expressed in grams instead of atomic mass units.
Use 35.5 for Cl

3. Find the Gram Formula MassesNa O2
NaCl
HBr
NaOH
Mg3N2
Al2(SO4)3

4. Percent Composition – composition as a percentage of each element compared to the total mass of the compound.

5. Find the Percent CompositionNa O2
NaCl
HBr
NaOH
Mg3N2
Al2(SO4)3

6. Hydrates – crystals that contain water.
Anhydrous – substances without water
To calculate % water, treat the water molecule as a single unit.

7. Calculate % Water
CuSO4∙5H2O

8. 11/6 Chemistry Aim: What calculations can we perform with formulas
11/6 Chemistry Aim: What calculations can we perform with formulas? Obj: SWBAT calculate moles, find molecular formulas, and set up mole ratios Do Now: What is the formula mass of NaOH? Homework: Worksheet

9. Moles Mole = number of atoms of carbon present in 12.000 g of C-12
Avogadro’s number = x 1023
Number of particles in a mole of a substance

10. Moles = grams / gram formula mass
Grams = moles x gram formula mass

11. What is the mass in grams of a 8.4 mole sample of iron?
Convert 0.45 g of sodium hydroxide, NaOH to moles.
How many moles of potassium nitrate, KNO3 are present in a sample with a mass of 85.2 g.
What is the mass in grams of 0.94 moles of sodium bicarbonate, NaHCO3?

12. Finding Molecular Formulas from Empirical Formulas
Find the formula mass of the empirical formula
Divide mass of compound by the mass of the empirical formula.
Multiply your empirical by that answer.

13. A compound has an empirical formula of CH2 and a molecular mass of 56 amu. What is its molecular formula?
A compound has an empirical formula of CH and a molecular mass of 78 amu. What is the molecular formula?

14. Mole Relations in Balanced Equations
Set up ratios
Also works for volumes of gases