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SavannahYear 8
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ScienceChemical reactions, acids and alkalis30 min★★★ difficulty

Acids, alkalis and neutralisation

The pH scale, indicators and one reliable reaction pattern: acid plus alkali gives a salt plus water. That pattern explains indigestion tablets, farming and cleaning products.

Part of your national curriculum
  • Chemistry: chemical reactions: Understand reactions of acids with alkalis to produce a salt plus water, and use the pH scale for measuring acidity

Lesson overview

What you'll learn in this lesson

Understand reactions of acids with alkalis to produce a salt plus water, and use the pH scale for measuring acidity

Key learning points

  • • Reading the scale
  • • Strong and weak, concentrated and dilute
  • • The reaction pattern
  • • Neutralisation you can see used

This lesson at a glance

  • 30 minutes
  • 18 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

reactionsalkalismeasuringacidityreading

Scroll down — the lesson carries on below

Part 1 of 18 · Discover6%
1

Watch & discover

Part 1 of 18

Watch first

Acids, alkalis and neutralisation

An English teaching video on this topic from Archie Science Show. Watch it, then scroll down for the lesson.

Do it for real

The practicals below use what the film shows, with a full method you can follow at home.

Making your own pH indicator

In a nutshell

Understand reactions of acids with alkalis to produce a salt plus water, and use the pH scale for measuring acidity

2

What you already know

Part 2 of 18

Before we start

What you already know

You should know that some substances are acidic and others alkaline.

Recap: Chemical reactions and balancing equations
3

Key words

Part 3 of 18

Key words

Words you'll need today

pH scale
A scale from 0 to 14 measuring acidity and alkalinity.
Indicator
A substance that changes colour according to pH.
Neutralisation
The reaction of an acid with a base or alkali to produce a neutral solution.
Salt
The compound formed when the hydrogen in an acid is replaced by a metal.
Alkali
A soluble base, which forms a solution above pH 7.
4

Learning cycle

Part 4 of 18

Learning cycle 1 of 2

The pH scale and indicators

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 18

Learn

Reading the scale

Below 7 is acidic, 7 is neutral, above 7 is alkaline. Stomach acid is around pH 2, lemon juice 3, pure water 7, soap about 9 and oven cleaner 13. Universal indicator gives a colour for the whole range; litmus only tells you which side of neutral you are on, so choose the indicator that answers your question.

6

Explore the idea

Part 6 of 18

Learn

Strong and weak, concentrated and dilute

Strong and weak describe the acid itself: hydrochloric acid is strong, ethanoic acid in vinegar is weak. Concentrated and dilute describe how much acid there is in a given volume of solution. A dilute strong acid can have a higher pH than a concentrated weak one, so the two pairs of words are not interchangeable.

7

Quick check

Part 7 of 18

Quick check

A solution of pH 3 is...

8

Reset break

Part 8 of 18

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
9

Quick check

Part 9 of 18

Quick check

Hydrochloric acid + sodium hydroxide gives...

10

Learning cycle

Part 10 of 18

Learning cycle 2 of 2

Neutralisation reactions

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 18

Learn

The reaction pattern

Acid + alkali gives salt + water. Hydrochloric acid + sodium hydroxide gives sodium chloride + water. Sulfuric acid + potassium hydroxide gives potassium sulfate + water. Naming the salt is a two-step job: the metal comes from the alkali, and the rest of the name comes from the acid - chloride from hydrochloric, sulfate from sulfuric, nitrate from nitric.

12

Explore the idea

Part 12 of 18

Learn

Neutralisation you can see used

Indigestion tablets contain a base to neutralise excess stomach acid. Lime is added to acidic soil so crops grow. Toothpaste is slightly alkaline to neutralise the acids bacteria produce. In each case pH is being moved towards 7 deliberately - and a titration with indicator is how you find exactly how much is needed.

13

Quick check

Part 13 of 18

Quick check

Which pair of terms describes amount of acid per volume?

14

Quick check

Part 14 of 18

Quick check

Lime is added to soil to...

15

Common mix-ups

Part 15 of 18

Common mix-ups

Things people often get wrong

  • Neutral is pH 7, not 'no pH'.
  • Strong is not the same as concentrated.
  • All alkalis are bases, but only soluble bases are alkalis.
  • Neutralisation always produces water as well as a salt.
16

Challenge round

Part 16 of 18

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

17

Mastery quiz

Part 17 of 18

Marked quiz

End of lesson quiz: Acids, alkalis and neutralisation

6 questions, marked with the reasoning shown. No timer.

  1. 1. Pure water has pH...

  2. 2. Sulfuric acid produces salts called...

  3. 3. Universal indicator is more useful than litmus because it...

  4. 4. An alkali is...

  5. 5. Neutralisation always produces...

  6. 6. Toothpaste is slightly alkaline to...

18

Lesson round-up

Part 18 of 18

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 18 · Watch & discover

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    Understand reactions of acids with alkalis to produce a salt plus water, and use the pH scale for measuring acidity

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