Chapter 1: Moles and equations
Resources available
Topic name
Syllabus
outcomes
Formulae and
equations
1.5a
Number of
lessons
(suggested)
1
Relative atomic
masses
1.1a, 1.3a, 1.3b
1
The mole and
Avogadro’s
constant
Empirical and
molecular
formulae
1.2a
1
1.4a, 1.4b
2
Reacting masses
1.5a, 1.5b(i)
1
Moles in solution
1.5b(iii)
6
Calculations
involving gas
volumes
Revision
1.5b(ii)
3
1.1 to 1.6
2
Coursebook
material
Key concepts
Chemical
formulae and
chemical
equations
Masses of atoms
and molecules;
Accurate relative
atomic masses
The mole and the
Avogadro
constant
Empirical
formulae
Molecular
formulae
Chemical
formulae and
chemical
equations
Solutions and
concentration
Experiments and
evidence
Calculations
involving gas
volumes
All sections of
Chapter 1
Experiments and
evidence
Teacher CD
resources
Experiments and
evidence
Experiments and
evidence
Experiments and
evidence
Practical 1.1
Experiments and
evidence
Experiments and
evidence
Practical 1.2
Practical 1.3
Practical 1.4
Practical 1.5
Practical 1.6
Practical 1.7
Practical 1.8
Experiments and
evidence
Topic 1: Formulae and equations
Chapter 1: Chemical formulae and chemical equations
Suggested activities
Starter:
•
What is a chemical formula? What does it tell us about a compound? What can we tell from the name of a compound?
a) The elements present.
b) The number of elements present. If the name ends in ‘-ide’ then there are two elements present. If the name ends in
‘-ate’ then there are three elements present and the third one is oxygen.
c) Do some examples. Try to use a selection of different examples.
Practical or activity 1:
•
Ask them to explain the purpose of a chemical equation. Why use a symbol equation instead of a word equation? Go
through how to balance equations (see support for struggling students).
Common misunderstandings and misconceptions
Many students ‘panic’ when confronted by an unbalanced equation. Their first instinct is to change the formulae. They must
be told that the formulae, once decided upon, must not be changed. After that numbers are placed in front of the formulae
to balance the equation.
Supporting struggling students
Give them a strategy to follow. They decide what is wrong with the equation and rectify it. This will inevitably make
something else wrong. This is then corrected and by going backwards and forwards the equation is balanced. Reassure them
that this can take quite a long time …
3CuO + 2NH3 → 3Cu + 3H2O + N2
The equation is now balanced!
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Topic 2: Relative atomic masses
Chapter 1: Masses of atoms and molecules; Accurate relative atomic masses
Suggested activities
Starter:
•
•
Revise work on atomic structure and the number of electrons, protons and neutrons.
Use the Periodic Table to look at the atomic (proton) number. This is always a whole number. But when we look at the
atomic mass their values are almost always not a whole number (or integer). Why is this? Remember that subatomic
particles are indivisible. We cannot have part of a neutron.
Activity 1:
•
•
•
Define the term ‘relative atomic mass’. Emphasise the words weighted average. Use chlorine as an example. It has two
isotopes: 35Cl and 37Cl. The average is 36Cl but the relative isotopic abundances are 75% 35Cl and 25% 37Cl. Show the
calculation and why the Ar is 35.5.
Explain how the relative isotopic abundances are found.
This is one instance where careful consideration of the definition guides the calculation.
Common misunderstandings and misconceptions
Students sometimes think you add up the isotopic masses and find the average rather than the weighted average. This will
have been addressed by looking at the chlorine example.
Supporting struggling students
As long as they have access to a calculator then there is no reason why weaker students should find this particularly difficult.
•
Using chlorine as an example the template is:
1) Let there be 100 atoms
2) a) 75 of these have mass of 35 atomic mass units, i.e. 2625 amu
b) 25 have mass of 37 atomic mass units, i.e. 925
c) Add these together, giving a total of 3550 amu
d) Divide by 100 to get the relative mass for one atom = 35.5
Challenging high achievers
Ask them to produce a spreadsheet to ‘automate’ their calculations.
Homework suggestion
End-of-chapter questions 1 and 2.
Topic 3: The mole and Avogadro’s constant
Chapter 1: The mole and the Avogadro constant
Suggested activities
Starter:
•
•
How small are particles? So small that they are impossible to count. Give various stories that illustrate this. More able
students can be asked to calculate how long it would take to count out the number of water particles in 1 cm3 of water at
the rate of 1 every second. Answer 6.4 × 1016 years.
Therefore, we express in terms of the mole. ‘We weigh out numbers of particles’. See page 5 of the Coursebook for the
definition of a mole.
Activity 1:
•
Use SAQs (self-assessment questions) as an introduction to the calculations of moles and masses.
Activity 2:
•
Now look at numbers of moles by using SAQ 3 and 4. This will test their understanding of formulae and the mole.
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Common misunderstandings and misconceptions
The mole is a difficult concept for some students. Sometimes it is better to not labour the point and rely on a gradual
‘osmosis’ as they understand the concept over time.
Supporting struggling students
A calculation triangle may help them remember the formulae.
Challenging high achievers
Ask them to make up their own problems.
Homework suggestion
End-of-chapter questions that have not been completed in the lesson.
Topic 4: Empirical and molecular formulae
Chapter 1: Empirical formulae; Molecular formulae
Suggested activities
Starter:
•
Define the terms ‘empirical formulae’ and ‘molecular formulae’.
Practical or activity 1:
•
Go through the SAQ.
Practical or activity 2:
•
Introduce the practical they are to do in the next lesson (practical 1.1). They are to find the empirical formula of
CuSO4.5H2O. Show the class what happens when the solid is heated gently. Ask the class how they think they would
find the number of water molecules loosely attached to the copper(II) sulfate.
•
The concept of the practical is quite easy but it is not so easy in practice. The Bunsen flame should be on blue but very
low and the mixture should be stirred continuously.
Common misunderstandings and misconceptions
The molecular formula is not always a multiple of the empirical formula, i.e. quite often the molecular formula is the same as
the empirical formula.
Supporting struggling students
Using worked examples is probably the best strategy here, with a reduction in help with each succeeding example.
Homework suggestion
End-of-chapter questions that have not been completed in lesson.
Topic 5: Reacting masses
Chapter 1: Chemical formulae and chemical equations
Suggested activities
Starter:
•
Chemists and chemical engineers want to know how efficient their processes are. But to do that we have to know the
amounts of what we start out with and what we should end up with. Ask the class how we might be able to do that.
Practical or activity 1:
•
The class is given an example to illustrate this and is then asked to work through some simple examples.
Practical or activity 2:
•
The students can answer the SAQs from the Coursebook.
Common misunderstandings and misconceptions
Many students who are not natural mathematicians can find this topic tricky. See below for hints on this.
Challenging high achievers
The end-of-chapter questions are of the correct level and at this stage are good tests for them.
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Supporting struggling students
A strategy for doing these questions is given on the worked example on page 7 of the Coursebook. However, some students
have a problem with Step 3. One way round this is to work out the answer for one gram and then scale up or scale down.
Homework suggestion
End-of-chapter questions give opportunities to reinforce the work done in the lesson.
Topic 6: Moles in solution
Chapter 1: Solutions and concentration
Suggested activities
Starter:
•
Review the concept of concentration and how it can be calculated. The class is given the formula for concentration and
n
are asked to manipulate the formula C =
to find n and then V.
V
Practical or activity 1:
•
The class goes through some simple calculations by converting cm3 to dm3.
Practical or activity 2:
•
The concept of a standard solution is introduced and the practical on practical sheet 1.4 explained. This is an important
procedure and should not be rushed. There are a lot of concepts and skills involved here.
•
The relative formula mass of the sodium carbonate is calculated.
•
The students have to work out the number of moles required for 250 cm3 of a 0.1 mol dm−3 solution.
•
They then have to make up the solution – they will need this skill for the practical exam.
Practical or activity 3:
•
The standard solution is titrated against HCl and the results used to standardise some hydrochloric acid.
Practical or activity 4:
•
The students use concentrations and moles to find the formula of hydrated sodium carbonate (washing soda). Practical
sheet 1.6 is used. The hydrochloric acid used can be that standardised using the standard sodium carbonate solution in
the previous lessons.
Practical or activity 5:
•
The concentration of calcium hydroxide solution has to be investigated. This takes their understanding to another level
because they have to choose the concentration of hydrochloric acid to use. (See practical sheet 1.7: ‘Finding the
concentration of a calcium hydroxide solution’.)
Practical or activity 6:
•
Use practical sheet 1.2. This can be done on a microscale basis and deals directly with stoichiometry of equations. This
activity could equally fit into the first lesson on formulae and equations.
Common misunderstandings and misconceptions
Because they are used to using cm3, students in practical work when measuring volumes do not immediately realise that the
volume is measured in dm3 when recording concentration (and so dm3 are also used in calculations). Therefore, 25 cm3 is
0.025 dm3, etc.
Challenging high achievers
Get them to discuss amongst themselves how they would work out the mass of sodium carbonate required. Get them to
explain to others how this could be done. The subsequent practical work also lends itself to discussion before embarking on
the task. This will benefit the high achievers who, by verbalising their strategies, will increase their ownership of their
learning.
Supporting struggling students
Seat them with a more able student so that the latter can explain the calculation – this helps both categories of student. Use
the calculations triangle using C, n and V (remembering that V is in dm3).
Homework suggestion
Use questions on the homework sheet. Complete write-ups of practicals.
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Topic 7: Calculations involving gas volumes
Chapter 1: Calculations involving gas volumes
Suggested activities
Starter:
•
Molar volumes – 1 mole of all ideal gases under the same conditions of temperature occupy the same volume at room
temperature and pressure (r.t.p.). This is 24 dm3 or 24 000 cm3. Ask the class why this is useful. The answer is because
gases cannot be weighed (at least not easily). One graphic example of this is to fill a gas syringe with hydrogen. The
syringe weighs less with the hydrogen than when it is empty.
Practical or activity 1:
•
The worked examples and following in-chapter questions from the Coursebook are a good introduction to the topic and
students should understand the basic principles by the time they have finished the questions or worked through some of
the examples.
Practical or activity 2:
•
The class then investigates the relative atomic mass of magnesium using gaseous volumes (see practical sheet 1.8). This
practical is carried out using microscale apparatus but can be adapted to a conventional scale quite easily.
Practical or activity 3:
•
From their work on molar volumes students should realise that equal volumes of gases under the same conditions of
temperature and pressure contain equal numbers of molecules (and hence moles). Therefore, under the same conditions
of temperature and pressure, if one gas occupies 10 cm3 and another gas occupies 20 cm3 then the second gas contains
twice as many gas molecules. Show some data on combustion data and show how the information can be used to find
the molecular formula of the gas.
Notes/comments:
•
Molar volumes incorporates Gay-Lussac’s Law and Avogadro’s hypothesis.
Common misunderstandings and misconceptions
As with moles in solution, the students should make sure they are aware what unit of volume they are working in and when
they express their results make sure that they are working with cm3 or dm3. Because they usually work in cm3 it may give
them a greater understanding of their answers to express them in cm3. However, if they are asked to measure volumes on an
industrial scale dm3 would be a preferred option.
Supporting struggling students
Use a calculation triangle, n =
Vgas
24
(if V is in dm3); help them rearrange the formula.
Challenging high achievers
As with the previous practicals, constructing groups where less able students are teamed with more able students supports the
former whist allowing the latter to improve their understanding by explaining concepts to others.
Homework suggestion
Complete the practical report and the questions.
Topic 8: Revision
Chapter 1: All sections
Suggested activities
Starter:
•
Go over checklists.
Practical or activity 1:
•
Use the homework sheet for this chapter to review the topic.
Notes/comments:
•
This is a revision lesson and therefore the resources used in this lesson can be taken from previous lessons. There are
also synoptic questions that take into account all of the concepts learned in this topic.
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•
One way of choosing which topics to revise is the ‘traffic lights’ system. Ask the class to indicate their level of
understanding of a concept.
RED
do not understand
AMBER partly understand
GREEN understand it fully
Those concepts and topics that obtain the most reds are the priority for revision.
Common misunderstandings and misconceptions
Consider all those highlighted in previous lessons if they proved to be a problem.
Supporting struggling students
Use whatever strategies have worked.
Challenging high achievers
Select exam questions that have caused problems (use examiner’s reports).
Homework suggestion
Revision.
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