Topic: Moles

Moles quiz

1. What is the meaning of the word mole in Chemistry?

Question 1 of 10

2. Balance the following equation: WO₃ + H₂ → W + H₂O

Question 2 of 10

3. Calculate the relative formula mass(Mr) of aluminium oxide (Al₂O₃)

Question 3 of 10

4. Complete the following expression: Mᵣ =

Question 4 of 10

5. What mass of calcium bromide will fully react with 71g of chlorine?

Question 5 of 10

6. What are the units for amount in Chemistry?

Question 6 of 10

7. Calculate the relative formula mass(Mr) of aluminium nitrate (Al(NO₃)₃)

Question 7 of 10

8. Complete the following expression: amount (in moles) =

Question 8 of 10

9. What do each of the following state symbols represent: (s), (l), (g), (aq)

Question 9 of 10

10. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

Question 10 of 10


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Flashcards: Moles

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Q&A slides – Moles

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Calculate reacting masses from experimental data – QUIZ

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1:25 write word equations and balanced chemical equations (including state symbols): for reactions studied in this specification and for unfamiliar reactions where suitable information is provided


Sodium (Na) reacts with water (H2O) to produce a solution of sodium hydroxide (NaOH) and hydrogen gas (H2).

Word equation:

     sodium + water –> sodium hydroxide + hydrogen

Writing the chemical equation

A chemical equation represents what happens in terms of atoms in a chemical reaction.

Step 1: To write a chemical equation we need to know the chemical formulae of the substances.

     Na + H2O –> NaOH + H2

Step 2: The next step is to balance the equation: write a large number before each compound so the number of atoms of each element on the left hand side (reactants) matches the number on the right (products). This large number is the amount of each compound or element.

During this balancing stage the actual formulas for each compound must not be changed. Only the number of each compound changes.

     2Na + 2H2O –> 2NaOH + H2

If asked for an equation, the chemical equation must be given.


State symbols are used to show what physical state the reactants and products are in.

State symbolsPhysical state
(aq)Aqueous solution (dissolved in water)


A solid piece of sodium (Na) reacts with water (H2O) to produce a solution of sodium hydroxide (NaOH) and hydrogen gas (H2).

     2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)

Balancing equations – Tyler de Witt videos

This excellent Tyler de Witt video is an introduction to balancing equations:

And here’s another of the lovely Tyler’s videos with some practice questions and answers on equation balancing:

1:26 calculate relative formula masses (including relative molecular masses) (Mᵣ) from relative atomic masses (Aᵣ)

Relative formula mass (Mr) is mass of a molecule or compound (on a scale compared to carbon-12).

It is calculated by adding up the relative atomic masses (Ar) of all the atoms present in the formula.


The relative formula mass (Mr) for water (H2O) is 18.

Water                     = H2O

Atoms present      = (2 x H) + (1 x O)

Mr                           = (2 x 1) + (1 x 16) = 18

Calculation of relative formula mass – Tyler de Witt video

Here’s an excellent Tyler de Witt video explaining how to calculate the relative formula mass of compounds with:

  • a simple formula
  • a formula which includes brackets
  • a formula which includes a dot (water of crystallisation)

1:27 know that the mole (mol) is the unit for the amount of a substance

In Chemistry, the mole is a measure of amount of substance (n).

The abbreviation for mole is mol.

The mass of 1 mole of a substance is the relative formula mass (Mr) of the substance in grams.


The Mr of water is 18.

Therefore the mass of 1 mol of water equals 18 g.

1:28 understand how to carry out calculations involving amount of substance, relative atomic mass (Aᵣ) and relative formula mass (Mᵣ)

The following formula allows for the interconversion between a mass in grams and a number of moles for a given substance:

    \[Amount(mol) = \frac{mass(g)}{M_r} \]

Example 1:

Calculate the amount, in moles, of 8.8 g of carbon dioxide (CO2).

Step 1: Calculate the relative formula mass (Mr) of carbon dioxide (CO2).

    \[Carbon\,dioxide = CO_2 \]

    \[Atoms\,present = (1 \times C) + (2 \times O) \]

    \[M_r = (1 \times 12) + (2 \times 16) = 44 \]

Step 2: Use the formula to calculate the amount in moles.

    \[Amount = \frac{mass(g)}{M_r} \]

    \[Amount = \frac{8.8}{44} \]

    \[Amount = 0.2 mol \]

Example 2:

Calculate the mass of 2 mol of copper(II) sulfate (CuSO4).

Step 1: Calculate the relative formula mass (Mr) of copper(II) sulfate (CuSO4).

    \[copper(II)\,sulfate = CuSO_4 \]

    \[Atoms\,present = (1 \times Cu) + (1 \times S) + (4 \times O) \]

    \[M_r = (1 \times 63.5) + (1 \times 32) + (4 \times 16) = 159.5 \]

Step 2: Rearrange the formula to calculate the mass.

    \[mass = amount \times M_r \]

    \[mass = 2 \times 159.5 \]

    \[mass = 319g\]

Calculations involving mass (in grams), amount (in moles) and relative atomic mass – Tyler de Witt video

This video shows how to perform calculations involving mass (in grams), amount (in moles) and relative atomic mass:

1:29 calculate reacting masses using experimental data and chemical equations

Example: When calcium carbonate (CaCO3) is heated calcium oxide is produced. You can use reacting mass calculations to calculate the mass of calcium oxide produced when heating 25 g of calcium carbonate.

     CaCO3     –>         CaO      +      CO2

Step 1: Calculate the amount, in moles, of 25 g of calcium carbonate (CaCO3)

    \[M_r(CaCO_3)=(1 \times 40) + (1\times12) + (3 \times 16) \]

    \[M_r(CaCO_3)= 100\]

    \[Amount = \frac{mass(g)}{M_r} \]

    \[Amount = \frac{25}{100} \]

    \[Amount = 0.25 mol \]

Step 2: Deduce the amount, in moles, of CaO produced from 0.25 mol of CaCO3.

This step involves using the ratio of CaCO3 to CaO from the chemical equation.

     CaCO3     –>         CaO      +      CO2

From the equation you can see that the ratio of CaCO3 to CaO is 1:1.

Therefore if you have 0.25 mol of CaCO3 this will produced 0.25 mol of CaO.

Step 3: Calculate the mass of 0.25 mol of CaO.

    \[M_r(CaO)=(1 \times 40) + (1 \times 16) \]

    \[M_r(CaO)= 56\]

    \[Mass(CaO)=amount \times M_r \]

    \[Mass(CaO)= 0.25 \times 56\]

    \[Mass(CaO)= 14g\]


A simple format for laying out this method can be used.

Example: What mass of ammonia (NH3) is formed when 7 g of nitrogen (N2) is combined with hydrogen (H2).



Calculate Reacting Masses video

This video steps through a very useful method used to calculate reacting masses.

2020-02-07T14:47:28+00:00Categories: Uncategorized|Tags: , , , , |
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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals

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