Grams (Mass) Examples: 47 Problems with Answers

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Grams (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

A gram (g) is the standard working unit of mass in chemistry, defined as one thousandth of a kilogram (the SI base unit of mass).

Grams tell you how heavy something is. A paperclip is about 1 gram. Moles tell you how many particles you have—a completely different question.

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: Grams (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 grams (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?

Worked Examples

Example 1

easy

Convert

2.50

moles of sodium chloride (NaCl) to grams. (Molar mass of NaCl =

58.44\,\text{g/mol}

)

Answer

146.1 g of NaCl

First step

Use the relationship: mass (g) = moles × molar mass.

Full solution

2
$m = 2.50\,\text{mol} \times 58.44\,\text{g/mol}$ .
3
$m = 146.1\,\text{g}$ .

Grams are the standard mass unit used in laboratory chemistry. The molar mass serves as the conversion factor between moles (the counting unit) and grams (the measurable unit on a balance).

Example 2

medium

How many moles are in

49.0

g of sulfuric acid (

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

)? How many molecules does this represent? (Molar mass =

98.09\,\text{g/mol}

)

Example 3

medium

How many grams of glucose (

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

M=180\,\text{g/mol}

) are needed to prepare

0.500\,\text{L}

of a

0.250\,\text{M}

solution?

Example 4

medium

How many grams of Fe

_2

_3

(

M=160

) are needed to react with excess CO in

\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2

to produce

11.2\,\text{g}

Fe (

M=55.85

Example 5

hard

How many grams of AgNO

_3

(

M=170

) are needed to react with excess NaCl to produce

14.35\,\text{g}

AgCl (

M=143.5

)? Reaction:

\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3

Example 6

hard

A reaction yields

4.5\,\text{g}

of product but the theoretical yield is

5.0\,\text{g}

. Find the percent yield.

Example 7

challenge

A mixture of

4.0\,\text{g}

_4

(

M=16

) and

16\,\text{g}

_2

(

M=32

) reacts via

\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}

. Find the limiting reagent and grams of CO

_2

produced. (

M_{CO_2}=44

)

Practice Problems

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

Example 1

medium

What mass in grams of iron is needed to provide

2.00 \times 10^{24}

atoms of iron? (Fe =

55.85\,\text{g/mol}

)

Example 2

hard

In the reaction

2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3

, calculate the mass in grams of

\text{AlCl}_3

produced from

13.5

g of aluminum reacting with excess chlorine. (Al =

26.98

, Cl =

35.45\,\text{g/mol}

)

Example 3

medium

How many grams are in

0.30\text{ mol}

H_2SO_4

(

M=98\text{ g/mol}

Example 4

easy

How many grams are in

2\text{ mol}

of carbon (

M=12\text{ g/mol}

Example 5

easy

How many moles are in

36\text{ g}

of water (

M=18\text{ g/mol}

Example 6

easy

Convert

2500\text{ g}

to kilograms.

Example 7

easy

Convert

0.75\text{ g}

to milligrams.

Example 8

easy

What is the mass of

0.5\text{ mol}

NaCl

(

M=58.5\text{ g/mol}

Example 9

easy

Is a gram a unit of mass or of amount of substance?

Example 10

easy

How many grams are in

3\text{ mol}

of oxygen gas

O_2

(

M=32\text{ g/mol}

Example 11

easy

How many moles are in

50\text{ g}

CaCO_3

(

M=100\text{ g/mol}

Example 12

medium

2H_2 + O_2 \rightarrow 2H_2O

, how many grams of water form from

4\text{ g}

H_2

? (

H_2=2

H_2O=18\text{ g/mol}

)

Example 13

medium

How many grams of

O_2

react with

0.25\text{ mol}

CH_4

CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

? (

O_2=32

)

Example 14

medium

What mass of

C

(

M=12

) contains the same number of moles as

32\text{ g}

O_2

(

M=32

Example 15

medium

How many grams are in

1.5\times 10^{24}

molecules of

H_2O

? (

N_A = 6\times 10^{23}

M=18

)

Example 16

medium

0.20\text{ mol}

sample of a compound weighs

11\text{ g}

. What is its molar mass?

Example 17

medium

How many grams of

NaOH

(

M=40

) are needed to make

0.5\text{ L}

of a

2\text{ M}

solution?

Example 18

medium

Convert

0.05\text{ kg}

CO_2

(

M=44

) to moles.

Example 19

medium

How many grams of product

H_2O

form from

5\text{ g}

H_2

reacting with excess

O_2

? (

H_2=2

H_2O=18

2H_2+O_2\rightarrow 2H_2O

)

Example 20

challenge

A mixture contains

4\text{ g}

He (

M=4

) and

28\text{ g}

N_2

(

M=28

). What is the total number of moles, and the mass percent of He?

Example 21

challenge

A hydrate

MgSO_4\cdot xH_2O

has mass

24.6\text{ g}

and contains

12.0\text{ g}

MgSO_4

(

M=120

) and the rest water (

M=18

). Find

x

Example 22

challenge

How many grams of

O_2

(

M=32

) are produced from decomposing

24.5\text{ g}

KClO_3

(

M=122.5

)? (

2KClO_3 \rightarrow 2KCl + 3O_2

)

Example 23

easy

How many grams are in

4\,\text{mol}

of helium (

M=4\,\text{g/mol}

Example 24

easy

How many moles are in

44\,\text{g}

of CO

_2

(

M=44\,\text{g/mol}

Example 25

easy

What is the molar mass of MgO (

\text{Mg}=24,\,\text{O}=16

Example 26

easy

How many grams of N

_2

(

M=28\,\text{g/mol}

) are in

0.25\,\text{mol}

Example 27

medium

Find the molar mass of

\text{Ca}(\text{NO}_3)_2

(

\text{Ca}=40,\,\text{N}=14,\,\text{O}=16

Example 28

medium

\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3

, how many grams of NH

_3

(

M=17

) form from

14\,\text{g}

of N

_2

(

M=28

Example 29

medium

How many moles are in

25.0\,\text{g}

of NaCl (

M=58.5

Example 30

medium

A jewelry piece contains

4.50\,\text{g}

of gold (

M=197

). How many moles of gold does it contain?

Example 31

medium

How many grams of CaCO

_3

(

M=100

) form from

0.40\,\text{mol}

Ca in

\text{Ca} + \text{C} + \frac{3}{2}\text{O}_2 \rightarrow \text{CaCO}_3

Example 32

medium

How many grams of glucose (

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

M=180

) contain

3.01 \times 10^{23}

molecules? (

N_A=6.02\times 10^{23}

)

Example 33

medium

What is the mass percent of N in NH

_4

_3

(

M=80

, atomic N=14)?

Example 34

hard

How many grams of H

_2

O (

M=18

) form from burning

32\,\text{g}

_4

(

M=16

) in

\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}

Example 35

hard

How many grams of CO

_2

(

M=44

) are produced from burning

46\,\text{g}

ethanol C

_2

_5

OH (

M=46

)? Reaction:

\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}

Example 36

hard

\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3

14\,\text{g}

_2

reacts with

6\,\text{g}

_2

. Find the limiting reagent and grams of NH

_3

formed. (

M

: N

_2

=28, H

_2

=2, NH

_3

=17)

Example 37

hard

What mass of

\text{KMnO}_4

(

M=158

) is needed to prepare

2.00\,\text{L}

of a

0.0500\,\text{M}

solution?

Example 38

hard

How many grams are in

9.03\times 10^{22}

atoms of carbon? (

N_A=6.02\times 10^{23}

M_C=12

)

Example 39

hard

A hydrate

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

has total mass

5.00\,\text{g}

and contains

3.20\,\text{g}

CuSO

_4

(

M=160

). The rest is water (

M=18

). Find

x

Example 40

challenge

0.500\,\text{g}

sample of an unknown metal M reacts completely with excess HCl to release

0.0200\,\text{mol}

_2

via

\text{M} + 2\text{HCl} \rightarrow \text{MCl}_2 + \text{H}_2

. Identify M by molar mass.

← Back to Grams (Mass) Practice Mode

Related Concepts

Mole Molar Mass