Molar Ratios and Stoichiometry

CHEMISTRY SEMESTER 2

Coefficient of
moles given

Coefficient of
moles unknown

Mole to Mole

Molar Ratio

The coefficients in a balanced chemical
equation tell us the mole ratios of the

reactants and products.

Whichever unit you start with will be the same
unit on the bottom of the first "train track"
Remember when mole on top of mole you
MUST look at the coefficients in the equation

2 : 1 : 2

# moles given

= moles
unknown

Formula for Mole to Mole Stoichiometry

Multiple Choice

Use the balanced equation to answer the following question.

3 Ba(NO₃)₂ + 2 Na₃PO₄ --> Ba₃(PO₄)₂ + 6 NaNO₃

i. 3 Ba(NO₃)₂ : 3 Ba(NO₃)₂ ii. 3 Ba(NO₃)₂ : 2 Na₃PO₄

iii. 3 Ba(NO₃)₂ : 1 Ba₃(PO₄)₂ iv. 3 Ba(NO₃)₂ : 6 NaNO₃

What are the possible molar ratios for 3 Ba(NO₃)₂ in the following equation?

• I and II

• III and IV

• I, II, III, and IV

• II, III, and IV

Multiple Choice

Use the balanced equation to answer the following question.

2 FeCl₃ + MgO --> Fe₂O₃ + 3 MgCl₂

How many moles of iron chloride (FeCl₃) will be produced from 5.50 moles of magnesium oxide (MgO)?

• 5.50 mol FeCl₃

• 11.0 mol FeCl₃

• 2.25 mol FeCl₃

• 3.67 mol FeCl₃

Whatever unit you start with, must go on the bottom.

Mole & Mass

Coefficient of
Moles Given

Coefficient of
Moles Unknown

= Mass Unknown

1 Mole Unknown

Molar Mass (PT)
of Unknown (g)

Molar Mass (PT)

Given (g)

Coefficient of
Moles Unknown

= Moles
Unknown (mol)

1 Mole Given

Coefficient of
Moles Given

The hardest part of these types of problems is stopping. Before

beginning these calculations, please check the starting and ending

units to ensure you get the correct answer.

​# Moles Given

Grams Given

Multiple Choice

Use the balanced equation to answer the following question.

4 NH₃ + 5 O₂ → 4 NO + 6 H₂O

How many grams of nitrogen monoxide (NO) will be produced from 2.50 moles of oxygen (O₂)?

Molar Mass NO: 30.01 g/mol Molar Mass O₂: 32.00 g/mol

• 60.0 g NO

• 64,.0 g NO

• 2.00 g NO

• 75.0 g NO

Multiple Choice

Use the balanced equation to answer the following question:

2 C₂H₆ + 7 O₂ --> 4 CO₂ + 6 H₂O

Given 8.25 grams of ethane (C₂H₆), how many moles of carbon dioxide (CO₂) will be produced?

• 0.27 mol CO₂

• 0.55 mol CO₂

• 16.5 mol CO₂

• 0.405 mol CO₂

Mass to Mass
Stoichiometry

When completing these calculations, please be sure that your units cancel.

This means whatever unit you start with MUST match the following bottom unit.

The words or numbers in color represent something other than 1.

Coefficient of
Moles Given

Coefficient of
Moles Unknown

= Mass Unknown (g)

1 Mole Unknown

Molar Mass (PT)
of Unknown (g)

Molar Mass (PT)

Given (g)

1 Mole Given

# Mass Given

Multiple Choice

Use the balanced equation to answer the following question.

3 Ca(OH)₂ + 2 H₃PO₄ --> Ca₃(PO₄)₂ + 6 H₂O

Molar mass of Ca(OH)₂: 74.10 g/mol Molar mass of Ca₃(PO₄)₂: 310.18 g/mol

How many grams of calcium hydroxide (Ca(OH)₂) are required to produce 65.1 grams of calcium phosphate (Ca₃(PO₄)₂)?

• 0.21 g Ca(OH)₂

• 46.7 g Ca(OH)₂

• 23.3 g Ca(OH)₂

• 272.5 g Ca(OH)₂

Mole to Mole Stoichiometry: 1 Train Track

Mole to Gram Stoichiometry: 2 Train Tracks

Gram to Mole Stoichiometry: 2 Train Tracks

Gram to Gram Stoichiometry: 3 Train Tracks

Stoichiometry Calculations

Dropdown

For a stoichiometry problem converting moles to moles, there will be ​

Select answer

. For a stoichiometry problem converting moles to grams, there will be ​

Select answer

. For a stoichiometry problem converting grams to grams, there will be ​

Select answer

.

This value comes from a
calculation or question
will state "theoretical"

mass.

Theoretical Yield

This value is a representation of
how successful a reaction is. If the
number is closer to 100% then the

reaction is more successful.

Percent Yield

This number comes from lab
measurements. This value will

typically be less than the

theoretical yield.

Actual Yield

Theoretical Yield

Actual Yield

x 100

Multiple Choice

The following reaction is carried out:

2 Na + Cl₂  --> 2 NaCl

The mass of the reactant Na is 47.0 g and the mass of the reactant chlorine is 35.0 g. The final mass of NaCl produced is found to be 63.5 g. What is the percent yield of the reaction?

• 55.1%

• 74.5%

• 77.4%

• 129.1%

Once the limiting reactant
is consumed, the reaction is

complete.

Controls Reaction

Look at the data table

and determine what is left
after the reaction. That's

your excess reactant.

Read the Data

The excess reactant will be

left over even after the
reaction is complete.

Excess Reactant

LIMITING REACTANT

Multiple Choice

A classic chemistry class demonstration is the burning of copper (II) chloride with a Bunsen burner for flame lab. In this demonstration, two chemical reactions are occurring: the burning of methane gas and the reaction between oxygen and copper (II) chloride. Of the two reactions, what is the only limiting reactant?

• Oxygen Gas consumed by combustion in the bunsen burner.

• Methane Gas from the gas supply.

• Copper (II) chloride salt that is burned.

• None of the above.