Core Practical 2

Introducing the Practical

This practical focuses on recording the pH at intervals when calcium hydroxide or calcium oxide reacts with dilute hydrochloric acid.

An initial mass of the solid must be added to a fixed volume of the acid, and the pH recorded each time more of the solid is added to the acid.

The pH can be recorded using a pH meter, or universal indicator paper with a glass rod used to take a pH measurement at each interval.

As a general rule, eye protection (goggles) must be worn for all practicals.

This risk assessment is provided as an example only, and you must perform your own risk assessment before doing this experiment.

Hazard	Possible Harm	Precuation
calcium hydroxide powder	skin irritation, serious eye damage, may cause respiratory irritation	wear gloves and avoid making a dust
hydrochloric acid	concentrated acid is corrosive and damages skin and clothes	use dilute hydrochloric acid (only an irritant, wash hands if spillage)

use a measuring cylinder to add 20 ml of dilute hydrochloric acid to a beaker
dip a clean glass rod into the contents of the beaker, then use it to transfer a drop of liquid to a piece of universal indicator paper on a white tile
wait 30 seconds, then match the colour to a pH colour chart - and then record the estimated pH
add 0.3 g of calcium hydroxide powder to the beaker
stir thoroughly, then repeat steps 2 and 3
add another 0.3 g of calcium hydroxide powder to the beaker, and repeat steps 2-4 until you have added a total of 3.0 g of calcium hydroxide powder

Plot a graph to show how the change in pH was affected by the amount of calcium hydroxide added.

Use the graph to estimate the number of spatulas of calcium hydroxide needed to produce a neutral solution.