The reaction between an acid and an alkali

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

The reaction between an acid and an alkali
These activities investigate what happens to pH and temperature as an acid reacts with an alkali.

Observe what happens to the pH as an acid reacts with an alkali using a Universal Indicator
Method

1. Measure 20 cm³ of hydrochloric acid into a beaker using a measuring cylinder.
   
2. Add a few drops of Universal Indicator – sufficient to produce an obvious colour.
   
3. Place a thermometer in the solution and record its temperature.
   
4. Use a pH chart to record the pH of the solution.
   
5. Add 18 cm³ of sodium hydroxide solution to the mixture gradually and observe any colour changes.
   
6. Add the sodium hydroxide one drop at a time until we reach the pH of 7 (using the colour chart).
   
7. Indicate using a colour chart how the pH changed during the experiment.
   NaOH + HCl → NaCl + H₂O

Observe what happens to the temperature as an acid reacts with an alkali
Method

1. Measure 50 cm³ of hydrochloric acid into a plastic cup using a measuring cylinder.
   
2. Measure 50 cm³ of sodium hydroxide solution into a second plastic cup using a measuring cylinder.
   
3. Measure the temperature of the hydrochloric acid.
   
4. Wash the thermometer and the measure the temperature of the sodium hydroxide solution.
   
5. When both solution are at the same temperature, add the sodium hydroxide solution to the acid. (Take care to avoid any loss of liquid).
   
6. Record the change in temperature
   (The heat of neutralization is the heat of reaction produced when a gram equivalent of a base or acid is neutralized with a gram equivalent of an acid or base in dilute solution)

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Questions

1. Explain how and why the temperature changed during the experiment.
   
2. What was done in the experiment to obtain accurate results?
   
   
   • Show Answers
     1. The temperature rises. This is because the neutralisation reaction is exothermic and gives out heat to the surroundings.
        
     2. To reduce heat loss: a plastic cup was used instead of a beaker, the cup was covered.
        Used a digital thermometer to record the temperature more accurately.

Neutralisation Reactions
Hazard Symbols Explained
The pH Scale & Indicators
Neutralisation Reactions (Acid + Base)
Investigating Indigestion Remedies

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