Chemistry
Ms. Boon
Name: ________________
Period: ____ Date: _______
Unit 3 Study Guide
Standard 3c: What is the mole?
The mole is a number we use to make counting atoms, ions, and molecules much easier.
 1 mole (mol) = 6.022 x 1023 particles.
 The number of particles in 1 mole is called Avogadro’s number.
 To convert from moles to particles (atoms or molecules), multiply by Avogadro’s number.
 To convert from # of particles (atoms or molecules), divide by Avogadro’s number.
Standard 3d: Molar mass and mole-gram conversions (
 The molar mass of an element is the mass of exactly one mole (6.022 x 1023 atoms) of that element. (Other names for molar
mass are “gram formula mass” and “molar weight”)
 The units for molar mass are g/mol. “g” is for gram and “mol” is for mole. We say this “grams per mole”.
 The molar mass of an element is the same number as the atomic mass. Just change the units from amu to g/mol.
How do I convert from number of moles to the mass in grams?
Why do I care? In chemistry class, we use the triple beam balance to measure the mass of different substances in grams. However,
the coefficients in chemical reaction equations tell us the number of moles of the reactants and products. We need to convert from
number of moles to mass in grams so that we know what mass of reactants to use in experiments.
Example Problem: The balanced chemical equation for the combustion of octane (gasoline) shows that 25 moles of oxygen gas (O 2)
are required in order to burn (combust) 2 moles of octane (C8H18). What is the mass (in grams) of 25 moles oxygen gas?
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O + energy
Step 1: Find the molar mass of O2 (16 x 2 = 32 g/mol)
Step 2: Multiply the molar mass by the number of moles. (32 g/mol) x (25 mol) = 800 g
How do I convert the mass in grams to number of moles?
Why? This is the opposite situation as above. Often, scientists have a certain amount of a reactant and they want to know if they
have enough to make a reaction happen. Converting from grams to moles will help us answer this type of question.
Example Problem: A chemist wants to synthesize salt from solid sodium and chlorine gas (2 Na (s) + Cl2 (g) → 2 NaCl (s)). The
chemist has 10g sodium. How many moles of sodium does she have?
Step 1: Find the molar mass of sodium. (23 g/mol)
Step 2: Divide the # grams given by the molar mass. (10g / 23g/mol = 0.43 mol sodium)
Standard 3a: Chemical Reactions (
Know the definitions of the following: reactant, product, subscript, coefficient, synthesis reaction, decomposition reaction,
combustion reaction, single replacement/displacement, double replacement/displacement. Be able to balance a chemical reaction
equation!
 Practice: Balance the equation and state what type of reaction it represents.
__Fe (s) + __ O2 (g) → __ Fe2O3 (s)
Standard 3e & 3f: Stoichiometry (
Vocabulary Review: Fill in the blanks (coefficients, percent, limiting, product, excess, mole, theoretical, molar mass, actual, balance)
All stoichiometric calculations involving equations use _________ ratios. When solving stoichiometric problems, you must
____________ the equation first. The _____________ in chemical equations provide mole ratios that can be used as conversion
factors. The conversion factor for converting between mass (g) and moles is the _______________ of the substance.
A(n) _________ reactant is not completely used up in a chemical reaction. A(n) _____________ reactant is used up first
and thus controls the quantity of _____________ that can be formed in a chemical reaction. The limiting reactant should be used to
calculate the ___________ yield. The __________ yield must be measured experimentally. The ____________ yield describes how
close the actual yield is to the theoretical yield.