Acids and alkalis are all around us; many everyday foods, drinks, cleaning products are acidic or alkaline.
Study the image of the pH scale "wheel". This scale gives a measure of the acidity or alkalinity of a substance. A value of pH 7 is regarded as neutral . Substances with a pH value greater than 7 are regarded as alkaline and those with pH value of less than 7 are acidic.
Acids can be neutralised by alkalis and alkalis can be neutralised by acids.
2.28 Activity 1. The Acid test
Use this simulation to find out the approximate pH of the range of substances available in the drop down list.
Prepare a table of results to record the pH values
2.28 -2.30 Activity 2. Using indicators
Students should:
- 2.28 describe the use of litmus, phenolphthalein and methyl orange to distinguish between acidic and alkaline solutions
- 2.29 understand how to use the pH scale, from 0–14, can be used to classify solutions as strongly acidic (0–3), weakly acidic (4–6), neutral (7), weakly alkaline (8–10) and strongly alkaline (11–14)
- 2.30 describe the use of universal indicator to measure the approximate pH value of an aqueous solution
Use the images to copy and complete the table below. Once completed, you should learn the colour changes for each indicator in each condition.
Solubility rules
2.28 - 2.30 Activity 3. Remember the colours. Complete the matching exercise below
2.31 Activity 4. Neutralisation
Students should:
- 2.31 know that acids in aqueous solution are a source of hydrogen ions and alkalis in a aqueous solution are a source of hydroxide ions
- 2.32 know that alkalis can neutralise acids
Work your way through the animation .
Note down the formulas and names of the acids involved.
2.33 Activity 5. Doing titrations
Students should:
- 2.33C describe how to carry out an acid-alkali titration
Titration is a laboratory technique which is used to to measure accurately the volume of a solution required to react completely with another solution.
If one of the solutions is of unknown concentration, the titration results can be used to do calculations to find it out.
The solution( of unknown concentration) is measured out accurately into a conical flask and a suitable indicator is added. The solution of known concentration is then added in measured amounts until the indicator changes.
Watch both videos and answer the questions below: