RP: Analysis + Purification of Water

What is the aim of the water purification required practical?

To analyse and purify water samples using appropriate techniques.

How can the pH of a water sample be measured?

Using universal indicator or a pH meter.

Why is a pH meter useful?

It provides a numerical pH reading.

How can dissolved solids in a water sample be investigated?

Evaporate a measured volume of water and examine or weigh the residue.

Why does evaporation leave dissolved solids behind?

The water evaporates, while non-volatile dissolved substances remain.

How can the mass of dissolved solids be determined?

Measure the mass of the dry residue after evaporating the water.

Why should an evaporating basin be weighed before use?

To allow the mass of residue to be determined by subtraction.

Why must the basin be dry before weighing?

Residual water would increase the measured mass.

Why should a water sample be heated carefully?

To avoid spitting, splashing and loss of dissolved solids.

How can distillation be used to purify water?

Water is boiled, vapour is cooled and the condensate is collected.

What is the purpose of the condenser in distillation?

To cool water vapour so it condenses into liquid water.

Why is the distillate generally purer than the original water sample?

Most non-volatile dissolved substances remain in the boiling flask.

Why should water samples of equal volume be used when comparing dissolved solids?

To make the comparison fair.

What is the independent variable when comparing different water sources?

The source or type of water sample.

What is the dependent variable when comparing dissolved solids?

The mass of dissolved residue.

Why should the same evaporation method be used for all samples?

To ensure consistent experimental conditions.

How can reliability be improved?

Repeat measurements and calculate a mean.

Why is distillation not necessarily sufficient to guarantee safe drinking water?

Some volatile contaminants may distil over, and additional treatment or testing may be needed.

Why must laboratory-produced distilled water not automatically be assumed potable?

It may have been contaminated by laboratory apparatus or chemicals.