Molar Mass Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Molar Mass.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

The mass in grams of exactly one mole of a substance, calculated by summing the atomic masses of all atoms in the chemical formula.

How much one mole weighs. For elements, it's the number on the periodic table.

Read the full concept explanation →

How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Molar Mass starts with the given amount, names the substance, and chooses the conversion factor that cancels the old unit.

Common stuck point: Students often know a formula related to molar mass but skip the recognition step: Am I using a mole bridge, molar mass, formula ratio, or balanced-equation ratio to connect measured amounts? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I using a mole bridge, molar mass, formula ratio, or balanced-equation ratio to connect measured amounts?

Common Mistakes to Watch For

Before you work through the examples, skim the mistake guide so you know which shortcuts and sign errors to avoid.

Moles Mistakes Stoichiometry Mistakes

Worked Examples

Example 1

easy

Calculate the molar mass of glucose (

\text{C}_6\text{H}_{12}\text{O}_6

Answer

M = 180.16\,\text{g/mol}

First step

6 \times 12.01 = 72.06\,\text{g/mol}

Full solution

2
H: $12 \times 1.008 = 12.10\,\text{g/mol}$ .
3
O: $6 \times 16.00 = 96.00\,\text{g/mol}$ .
4
Total: $72.06 + 12.10 + 96.00 = 180.16\,\text{g/mol}$ .

Molar mass is calculated by adding the atomic masses of all atoms in the formula. It tells us the mass of one mole of the substance.

Example 2

medium

What mass of calcium chloride (

\text{CaCl}_2

) contains

0.75

mol? (Ca = 40.08, Cl = 35.45 g/mol)

Example 3

medium

Calculate the molar mass of

\text{KMnO}_4

. (K = 39.1, Mn = 54.9, O = 16.0)

Example 4

medium

Find the molar mass of

\text{Al}_2(\text{SO}_4)_3

. (Al = 27, S = 32, O = 16)

Example 5

medium

Find the molar mass of

\text{Mg}_3(\text{PO}_4)_2

. (Mg = 24.3, P = 31.0, O = 16.0)

Example 6

hard

3.6\,\text{g}

of a hydrocarbon contains

0.20\,\text{mol}

. Find its molar mass and propose a formula in the

\text{CH}_x

family.

Example 7

hard

A compound is

40.0\%

6.7\%

53.3\%

O by mass and has molar mass

180\,\text{g/mol}

. Determine its molecular formula. (C = 12, H = 1, O = 16)

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

Calculate the molar mass of sulfuric acid (

\text{H}_2\text{SO}_4

). (H = 1.008, S = 32.07, O = 16.00)

Example 2

easy

What mass of calcium carbonate (

\text{CaCO}_3

) is equal to

0.250

mol? (Ca =

40.08

, C =

12.01

, O =

16.00

)

Example 3

easy

What is the molar mass of carbon (

C

)? (atomic mass 12)

Example 4

easy

What is the molar mass of water

H_2O

? (H=1, O=16)

Example 5

easy

What is the molar mass of

CO_2

? (C=12, O=16)

Example 6

easy

How many moles are in

36\text{ g}

of water? (

M = 18\text{ g/mol}

)

Example 7

easy

What is the mass of 3 mol of carbon? (

M = 12\text{ g/mol}

)

Example 8

easy

What is the molar mass of

NaCl

? (Na=23, Cl=35.5)

Example 9

easy

What is the molar mass of

O_2

? (O=16)

Example 10

easy

How many moles are in

58.5\text{ g}

NaCl

? (

M = 58.5

)

Example 11

medium

What is the molar mass of

Ca(OH)_2

? (Ca=40, O=16, H=1)

Example 12

medium

What is the molar mass of glucose

C_6H_{12}O_6

? (C=12, H=1, O=16)

Example 13

medium

How many moles are in

90\text{ g}

of glucose? (

M = 180\text{ g/mol}

)

Example 14

medium

What is the mass of 0.25 mol of

CaCO_3

? (Ca=40, C=12, O=16)

Example 15

medium

How many grams of

NaOH

are in 2 mol? (Na=23, O=16, H=1)

Example 16

medium

A 2 mol sample weighs

44\text{ g}

. What is its molar mass?

Example 17

medium

What is the molar mass of

(NH_4)_2SO_4

? (N=14, H=1, S=32, O=16)

Example 18

medium

What is the molar mass of

H_2SO_4

? (H=1, S=32, O=16)

Example 19

medium

How many grams of

CO_2

are in 0.5 mol? (

M=44

)

Example 20

challenge

A compound is 2 mol and

36\text{ g}

. If it contains only H and O in a 2:1 atom ratio, what is it?

Example 21

challenge

How many oxygen atoms are in

50\text{ g}

CaCO_3

? (

M=100

, O=16)

Example 22

challenge

100\text{ g}

of an oxide

MO

contains

0.5

mol. If O=16, what is the atomic mass of M?

Example 23

easy

What is the molar mass of

\text{N}_2

? (N = 14)

Example 24

easy

Find the molar mass of

\text{KCl}

. (K = 39.10, Cl = 35.45)

Example 25

easy

How many moles are in

50\,\text{g}

\text{CaCO}_3

? (

M = 100\,\text{g/mol}

)

Example 26

easy

What is the mass of

1\,\text{mol}

\text{HCl}

? (H = 1, Cl = 35.5)

Example 27

easy

What is the molar mass of

\text{MgO}

? (Mg = 24.3, O = 16.0)

Example 28

medium

What mass of

\text{Na}_2\text{CO}_3

is in

0.20\,\text{mol}

? (Na = 23, C = 12, O = 16)

Example 29

medium

How many moles are in

250\,\text{g}

\text{CaCl}_2

? (Ca = 40.08, Cl = 35.45)

Example 30

medium

Calculate molar mass of

\text{Fe}_2\text{O}_3

. (Fe = 55.85, O = 16.00)

Example 31

medium

Determine the mass of

0.10\,\text{mol}

\text{C}_2\text{H}_5\text{OH}

(ethanol). (C = 12, H = 1, O = 16)

Example 32

medium

What is the molar mass of

\text{Cu(NO}_3)_2

? (Cu = 63.5, N = 14, O = 16)

Example 33

medium

How many grams of

\text{C}_3\text{H}_8

(propane) is

2.0\,\text{mol}

? (C = 12, H = 1)

Example 34

hard

A compound has formula

\text{X}_2\text{O}_3

with molar mass

102\,\text{g/mol}

. (O = 16) Find the atomic mass of X.

Example 35

hard

200\,\text{g}

\text{NaOH}

is dissolved in water. How many moles of

\text{Na}^+

are released? (Na = 23, O = 16, H = 1)

Example 36

hard

How many grams of oxygen are in

98\,\text{g}

\text{H}_2\text{SO}_4

? (

M = 98

, O = 16)

Example 37

hard

Calculate the molar mass of hydrated copper sulfate

\text{CuSO}_4 \cdot 5\text{H}_2\text{O}

. (Cu = 63.5, S = 32, O = 16, H = 1)

Example 38

hard

What mass of

\text{KClO}_3

contains

48\,\text{g}

of oxygen? (K = 39, Cl = 35.5, O = 16)

Example 39

hard

0.500\,\text{mol}

of an unknown gas weighs

22.0\,\text{g}

. Identify the gas if it is a common diatomic.

Example 40

challenge

A mixture of

\text{NaCl}

and

\text{KCl}

weighs

5.85\,\text{g}

and contains

0.100\,\text{mol}

total. Find the mass of each. (NaCl = 58.5, KCl = 74.55)

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Related Concepts

Mole Atomic Mass Stoichiometry Concentration

Background Knowledge

These ideas may be useful before you work through the harder examples.

moleatomic mass