Here is a fun quiz for early year secondary students, Key Stage 3 (KS3; ages 11 to 14), to find out whether chemicals present in everyday life are acids or alkalis.
A brief introduction to increase the students’ knowledge and understanding of acids and alkalis prior to the quiz. Subjects to include:
- Acids – solutions of pure compounds in water. Corrosion. Strong and weak acids.
- Alkalis – examples of strong and weak alkalis.
- Neutral Substances.
- Litmus solution and paper tests.
- The pH scale.
- To give students the opportunity to consider the acidity or alkalinity of chemicals used in everyday life.
- To increase understanding of the pH scale and universal indicators to categorise the strength of acids and alkalis.
- The quiz will also develop analytical thinking, discussion and teamwork skills.
Materials & Methods
A list of cards and posters/slides required for the quiz. The quantity of cards will depend on class numbers. These can be laminated to keep in good condition for future use.
- 14 cards with the colours of universal indicator papers (figure 2).
- 14 cards with descriptions of acid and alkali strength (figure 2).
- Picture cards of item (chemical) with descriptions (figure 3).
- pH scale, with numbers and universal indicator colours (figure 1).
- Student scorecards, a table with item, pH, colour and strength columns (table 1) .
- Answers to scorecards – items, pH, colour and strength (table 2).
Students work in groups of 2 to 6, depending on class sizes, resources, and teacher’s discretion. Each group is provided with a scorecard and card sets: pictures, colours, and descriptions.
Firstly, the groups take a picture card of, for example, lemon juice, vinegar, washing powder or rainwater. They discuss whether the chemical in question is an acid, neutral or alkali, the pH number of the chemical and corresponding colour and description. A designated scribe records the predictions on the scorecard.
For example, if the item was car battery acid, the pH number would be zero, the colour red and the strength, very strong acid.
Scores are collated and a ‘prize’ given to the highest scoring group. The lesson could end with a whole class discussion on the pH scale/number of the items considered.
Figure 1: The pH scale, with numbers and universal indicator colours.
Figure 2: Universal indicator colours & strength descriptions.
Figure 3: Picture cards of item (chemical) with descriptions.
Table 1: Scorecard.
Table 2: Answers.
Presented at ASE Annual Conference Reading 2013
I compiled and presented this quiz for Dr Sue Howarth’s workshop: Giles, P. and Howarth, S. (2013) Acids and alkalis. TES resources were used.
T118 Crazy ideas in secondary science teaching that work
Dr Sue Howarth, Inst of Educ, Univ of Worcester. Organisation: University of Worcester
1130-1230 Henley business school 102: We will share some crazy – and not-so-crazy – ideas. Mostly the result of challenging Science PGCE and GTP student teachers, to take more risks in their lessons, these ideas have been tried and tested in classrooms/labs/outdoors and elsewhere. A booklet containing the best of their learning and teaching ideas will be given to those attending. It is hoped that some of the students, who came up with these ‘risky’ ideas, and are now NQTs, will help them present.
Overall conference theme: science for all. Disciplines: curriculum development research. Target audiences: 11-14 14-16 post 16 ITE Technicians Advisors. https://www.ase.org.uk/conferences/previous-annual-conferences/ase-annual-conference-2013-reading/?preview=true T118, p80.
Acids and alkalis (Gallagher and Ingram, 2001)
An important group of chemicals is called acids.
- They are solutions of pure compounds in water.
- Need to be handled carefully because they are corrosive. They can eat away metals, skin, and cloth.
- Some are not so corrosive even when concentrated. They are weak acids. Citric acid is a weak acid found in oranges and lemons.
You can tell if something is an acid, by its effect on litmus. Litmus is a purple dye. It can be used as a solution, or on paper.
- Litmus solution is purple. Litmus paper for testing acids is blue.
- Acids will turn litmus solution red.
- They will also turn blue litmus paper red.
|Strong acids||Weak acids|
|Hydrochloric acid||Ethanoic acid|
|Sulphuric acid||Citric acid|
|Nitric acid||Carbonic acid|
Some common acids and their formulas:
|Hydrochloric acid||HCl (aq)|
|Sulphuric acid||H2SO4 (aq)|
|Nitric acid||HNO3 (aq)|
|Citric acid||C6H8O7 (aq)|
|Ethanoic acid||CH3COOH (aq)|
There are many other weak acids that, like citric acid, occur naturally. Ethanoic acid is found in vinegar, and tannic acid on tea. Ant and nettle stings contain methanoic acid.
There is another group of chemicals that also affect litmus, but in a different way to acids. They are the alkalis.
Alkalis turn litmus solution blue and red litmus paper blue.
Like acids, they must be handled carefully, because they can burn skin.
|Strong alkalis||Weak alkalis|
Some common alkalis. Most alkalis are solids. However, they are usually used in laboratory as aqueous solutions. The main one are:
|Sodium hydroxide||NaOH (aq)|
|Potassium hydroxide||KOH (aq)|
|Calcium hydroxide||Ca(OH)2 (aq)|
|Ammonia solution||NH3 (aq)|
Many substances do not affect the colour of litmus solution, so they are not acids or alkalis. They are neutral. Sodium chloride and sugar solutions are both neutral.
The pH scale
Some acids are weaker than others. It is the same with alkalis. The strength of an acid or alkali is shown using the pH scale that goes from 0 to 14.
On this scale:
- An acidic solution has a pH number less than 7.
- An alkaline solution has a pH number greater than 7.
- A neutral solution has a pH number of exactly 7.
You can find the pH of any solution by using universal indicator. Universal indicator is a mixture of dyes. Like litmus, it can be used as a solution, or as universal indicator paper. It goes a different colour at different pH values.
Gallagher, R. and Ingram, P. (2001) Acids and bases. In: Coordinated science. Chemistry for Higher Tier. 3rd edition. Oxford University Press, pp. 44-51.