Moles and Stoichiometry

Ms. Randall

I. Moles• 1 mole is 6.02 x 1023 of anything!!

• 6.02 x 1023 is called Avogadro's number.

• A mole can be 6.02 x 1023 atoms or molecules

A Mole is a UnitSing-a-long!!!

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II. Interpreting Chemical Formulas

A. Empirical Formula

• Simplest ratio of atoms in a compound (Ex. C2H5)

• The subscript tells you how many moles of each ion in the compound.

• Ex. Al2O3 = 2 mol Al+3 3 mol O-2

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B. Molecular Formula• Actual ratios of atoms in a molecule or

compound (Ex. C4H10)

• Molecular formulas are whole-number multiples of an empirical formula

• Ex: C4H10 molecular formula

C2H5 empirical formula

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C. Structural Formula

• Shows the arrangement of the atoms in the actual compound

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III. Stoichiometry

• The study of quantitative relationships that can be derived from chemical formulas and equations

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• 1 mole of atoms has a mass equal to the atom’s atomic mass in grams.

• Atomic mass located on periodic table.

• Round to the nearest TENTH ( 0.1)

Example:

C= 12.0 amu = 12.0 g/mol

O= 16.0 amu = 16.0 g/mol

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B. Gram Formula Mass (GFM)

• the sum of all the atomic masses in the formula of the substance

1. add up the mass of each atom in the formula.

2. Multiply by the number of each atom if there is more than one of each atom.

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Element Atomic Mass # of Atoms in

Formula

Product

H 1 2 2

O 16 1 16

Total Mass = 18 g

Example: silver nitrate

Element # of atoms Mass Product

Ag = 1 × 108amu = 108 g

N = 1 × 14amu = 14 g

O = 3 × 16 amu = 48 g

170g/mol

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Regents Practice

The gram formula mass of NH4Cl is

(1) 22.4 g/mole

(2) 28.0 g/mole

(3) 53.5 g/mole

(4) 95.5 g/mole

N 1 x 14.0 =

H 4 x 1.0 =

Cl 1 x 35.5 = _______

g/mole

1. Calculating Moles from Mass

Formula on table T in reference table

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given mass (g)

Gram formula mass

Mole =

2. Calculating Grams from Moles

• Rearrange the formula in

table T to solve for grams

given mass (g)

Gram formula mass

Mole =

Mole x GFMGrams =

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Grams Moles÷ gfm

x gfm

Summary

• Step1: Find the formula mass of the substance and express it in grams per mole

• Step 2: Apply the formula

mol =grams_

GFM

mol =390g__

110 g/mol

= 3.5 mol

CaCl2Ca = 40 × 1 = 40Cl = 35 × 2 = 70

110 g/mol

What is the mass of 2 moles of sodium thiosulfate?

Na2S2O3

Na = 23 × 2 = 46S = 32 × 2 = 64O = 16 × 3 = 48

158 g/mol= GFM

grams = moles × GFM

= 2 mol × 158 g/mol

= 316 g

step 1

step 2