Acids and Bases teacher guidance

Review my learning 14–16 years

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Acids and bases: teacher guidance

This resource forms part of the Review my learning series from the Royal Society of

Chemistry. Additional support for addressing misconceptions identified using these

worksheets can be found at rsc.li/3mm0IeW.

These worksheets assess content from the 11–14 and 14–16 specifications. They can

be used to identify learners’ knowledge gaps and misconceptions following the

completion of that part of the curriculum.

The Acids and bases worksheets cover the following topics:

• the pH scale

• the pH of acidic and alkaline solutions

• common acids and alkalis

• general word equations for the reactions of an acid with a metal, metal

oxide, metal hydroxide and a metal carbonate

• chemical formulas of common laboratory acids

• types of salts produced from reactions with hydrochloric acid, sulfuric acid

and nitric acid

• universal and litmus indicators.

If learners successfully answer questions on these topics, they can attempt the

extension questions. These cover:

• word equations for the reactions between an acid and a metal, metal oxide,

metal hydroxide or metal carbonate

• symbol equations for the reactions between an acid and a metal, metal

oxide, metal hydroxide or metal carbonate.

Level 1 ( ) is a scaffolded worksheet in which learners select words from a word list

to complete sentences. Level 2 ( ) is a partially scaffolded worksheet in which

learners complete sentences. Level 3 ( ) is an unscaffolded worksheet in which

most of the tasks involve answering questions with a minimum of prompts.

The worksheets can be used in a variety of ways:

• as an assessment of learners’ knowledge at the beginning or end of a period

of teaching – the level of the worksheet used can be matched to the ability

of the learners

• as an assessment of knowledge during a period of teaching and after

learners have completed the relevant section of the specification

• as a revision tool prior to the relevant examination

• as a refresher exercise for teachers or non-subject specialists.

There is also scope to increase the level of the worksheets used as learners progress

through their curriculum.

Review my learning 14–16 years

Available from rsc.li/3kJ97IR

The ‘What do I understand?’ page is common to all levels of worksheet and can be

used both to identify areas needing whole class attention and as an indicator for

learners to help guide their revision.

The Teacher guidance provides model answers for each level and guidance on

learners’ misconceptions. Learners can use the model answers to self- or peer assess.

Answers

Acids and bases: knowledge check

1.1 scaffolded/partially scaffolded/unscaffolded

(a)–(c)

Guidance: Some learners will only label pH 1 and pH 14 as acidic or alkaline.

Emphasise that acids have pH values from 1 to 6 and alkalis from 8 to 14.

Learners may refer to strong and weak acids and alkalis. At this stage, they are

probably just referring to the pH of the solution. Understanding strong and weak

acids and alkalis and concentrated and dilute acids and alkalis requires

knowledge on a particle level, which learners have probably not yet

encountered.

1.2 scaffolded/partially scaffolded

(a) The pH scale measures the acidity or alkalinity of a solution.

(b) Acidic solutions have a pH less than 7.

(d) Alkaline solutions have a pH greater than 7.

Review my learning 14–16 years

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unscaffolded

(a) The pH scale measures the acidity or alkalinity of a solution.

(b) acid/acidic solutions

(d) alkali/alkaline solutions

Guidance: The knowledge required to answer this question is a repeat from

question 1.1, but learners need to be familiar with using similar terms, such as

alkaline and alkalinity. Learners also need to be aware that water is not the

only neutral substance. Many liquids and solutions have pH values of 7, such as

ethanol and sodium chloride solution.

1.3 scaffolded/partially scaffolded

(a) Three acids commonly found in school laboratories are hydrochloric acid,

nitric acid and sulfuric acid.

(b) An alkali commonly found in school laboratories is sodium hydroxide

solution.

unscaffolded

(a) hydrochloric acid, nitric acid, sulfuric acid

(b) hydrogen ions

Guidance: Familiarisation with laboratory reagents will help learners remember

chemical names. Because the word ‘acid’ is commonly used in fiction and the

media, learners usually have some familiarity with the term. ‘Base’ and ‘alkali’

are not commonly used terms and learners will not be so familiar with them.

Although hydrogen ions are present in all acid solutions, most hydrogen-

containing compounds are not acids. Simple models can be used to illustrate

that acids dissociate in solution to give hydrogen ions.

Learners commonly misuse the term ‘molecular’. Acid solutions contain

hydrogen ions and are not molecular. Likewise, alkaline solutions contain

hydroxide ions and are not molecular.

Review my learning 14–16 years

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1.4 scaffolded/partially scaffolded

(a) acid + metal → salt + hydrogen

(b) acid + metal oxide → salt + water

(d) acid + metal carbonate → salt + water + carbon dioxide

unscaffolded

(a) acid + metal → salt + hydrogen

(b) acid + metal oxide → salt + water

(d) acid + metal carbonate → salt + water + carbon dioxide

Guidance: Learners need to realise that sodium chloride is not the only salt.

A salt is produced when the hydrogen in an acid is replaced by a metal.

Simple models can be used to represent the equations.

1.5 scaffolded/partially scaffolded

(a) Two everyday acids you might find in your home are vinegar and lemon

juice.

(b) Two everyday bases you might find in your home are laundry detergent

and baking soda.

unscaffolded

(a) Two everyday acids you might find in your home are vinegar and lemon

juice.

(b) Two everyday bases you might find in your home are laundry detergent

and baking soda.

Guidance: Learners confuse alkalis and bases. See the Teacher guidance for

questions 2.5 and 2.6. Many learners consider acids to be very corrosive and

‘eat things away’ (an idea fuelled by fiction and the media). Acids commonly

found in the home are mostly weak acids with pH values greater than 3. Battery

acid is an exception.

Review my learning 14–16 years

Available from rsc.li/3kJ97IR

Acids and bases: test myself

2.1 scaffolded/partially scaffolded/unscaffolded

An indicator is a substance that changes colour depending on the pH of the

solution.

Guidance: Learners need to understand it is the indicator that changes colour,

not the acid or alkali solution.

2.2 scaffolded/partially scaffolded/unscaffolded

(a) Universal indicator is red in acidic solution.

(b) Universal indicator is blue in alkaline solution.

Guidance: This is recall of knowledge. The two indicators learners are probably

familiar with are universal indicator and litmus. Both turn red in solutions with a

pH of 1 and blue in solutions with a pH of 10–14. Learners need to appreciate

that there are other indicators which have different colour changes to universal

indicator and litmus.

2.3 scaffolded/partially scaffolded/unscaffolded

Universal indicator is red in a solution with a pH of 1.

Guidance: Learners could use the pH scale from the Knowledge check

worksheet to colour in the colours of universal indicator in different pH solutions.

2.4 scaffolded/partially scaffolded/unscaffolded

Litmus indicator solution turns red in acidic solutions and blue in alkaline

solutions.

Guidance: If learners are investigating this practically, they may find it easier to

use both red and blue litmus paper to see the colours.

Review my learning 14–16 years

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2.5 scaffolded/partially scaffolded

A base is any substance that reacts with an acid to form a salt and water.

For example, copper oxide is a base.

unscaffolded

A base is any substance that reacts with an acid to form a salt and water.

2.6 scaffolded/partially scaffolded/unscaffolded

Alkalis are soluble bases and have a pH greater than 7. For example, sodium

hydroxide is an alkali.

Guidance: Learners may get confused with the terms ‘base’ and ‘alkali’. They

are probably only familiar with using the alkali sodium hydroxide solution. They

need to know that bases are chemicals which react with acids in neutralisation

reactions. They are usually metal oxides, metal hydroxides or metal carbonates.

Examples are copper oxide and copper carbonate. Many bases are insoluble

in water, but if the base is soluble in water, it is also called an ‘alkali’.

2.7 scaffolded/partially scaffolded/unscaffolded

A neutralisation reaction occurs when an acid reacts with an alkali.

Guidance: This is recall of knowledge. A common view of neutralisation is that

an alkali cancels out an acid – an alkali may stop the action of an acid.

2.8 scaffolded/partially scaffolded/unscaffolded

(a) Hydrochloric acid produces chlorides.

(b) Sulfuric acid produces sulfates.

Guidance: Learners may understand that part of the name of the acid is in the

name of the salt, but they need to ensure they have the correct suffixes.

Review my learning 14–16 years

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2.9 scaffolded/partially scaffolded/unscaffolded

The salt made when copper oxide reacts with sulfuric acid is copper sulfate.

Guidance: The comments for question 2.8 also apply to question 2.9. Knowing

that (in this example) the name of the salt contains a metal from the base and

a non-metal part from the acid, may help learners answer this correctly.

2.10 scaffolded/partially scaffolded

(a) hydrochloric acid H

(b) sulfuric acid HNO

unscaffolded

(a) hydrochloric acid: HCl

(b) sulfuric acid: H

Guidance: Learners need to be familiar with chemical formulas to answer this

correctly.

Review my learning 14–16 years

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Acids and bases: feeling confident?

3.1 scaffolded/partially scaffolded/unscaffolded

(a) Hydrochloric acid reacting with sodium hydroxide:

hydrochloric acid + sodium hydroxide → sodium chloride + water

(b) Sulfuric acid reacting with sodium hydroxide:

sulfuric acid + sodium hydroxide → sodium sulfate + water

nitric acid + sodium hydroxide → sodium nitrate + water

Guidance: The problem with writing word equations is that learners cannot

always identify the elements contained in the substances from the names.

They need some simple understanding of nomenclature.

3.2 scaffolded/partially scaffolded/unscaffolded

(a) HCl + NaOH → NaCl + H

(b) H

+ 2NaOH → Na

+ 2H

+ NaOH → NaNO

+ H

Guidance: Learners are required to select the correct formula and balance the

symbol equations. Common errors are:

• not understanding the use of subscripts in a formula

• not understanding that a large number in front of a formula multiplies the

whole formula by that number

• changing the formula of a substance to make the equation balanced

• inserting large numbers in the middle of a formula to balance the

equation.

Writing and balancing chemical equations is a difficult topic for many learners

and a skill that develops throughout their course.

Review my learning 14–16 years

Available from rsc.li/3kJ97IR

Acids and bases: what do I understand?

Mini-topic Assessed via:

I can describe the pH scale. Q1.1, Q1.2

I know the pH of acidic and alkaline

solutions.

Q1.1, Q1.2

Q2.5, Q2.6

I can name common acids and alkalis.

Q1.3, Q1.5

Q2.5, Q2.6

I can write general word equations for

reactions of an acid with a:

• metal

• metal oxide

• metal hydroxide

• metal carbonate.

Q1.4

I know the chemical formulas for common

laboratory acids.

Q2.10

I can name types of salt produced by

reactions with:

• hydrochloric acid

• sulfuric acid

• nitric acid.

Q2.8

I can use universal and litmus indicators to

identify acidic, alkaline and neutral

solutions.

Q2.1 (partially), Q2.2, Q2.3, Q2.4

Feeling confident? topics Assessed via:

I can write word equations for reactions

between an acid and a:

• metal

• metal oxide

• metal hydroxide

• metal carbonate.

Q3.1

I can write symbol equations for reactions

between an acid and a:

• metal

• metal oxide

• metal hydroxide

• metal carbonate.

Q3.2