Quick answer: A formula shows the ratio of atoms or ions in a substance, and for ionic compounds the charges must cancel. This Chemistry 9-10 lab on balancing equations gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
When two clear solutions are mixed, a solid sometimes appears. This lab tests five pairs of solutions, records what forms and uses the ion charges to name the solid, so you can write full balanced equations and ionic equations from your own observations.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-7
Aim
To mix pairs of solutions, identify the precipitates that form, and write balanced and ionic equations for each.
Equipment
- 0.1 mol/dm³ solutions of sodium hydroxide, copper(II) sulfate, iron(III) chloride, magnesium sulfate, calcium chloride and sodium carbonate
- Test tubes, rack, droppers, white card, marker, goggles
Safety
Wear goggles. Sodium hydroxide solution can irritate skin and eyes: wash splashes with plenty of water. Copper(II) sulfate is harmful if swallowed. Wash your hands afterwards.
Method
- Put 2 cm³ of one metal salt solution in a test tube standing in front of a white card.
- Add 2 cm³ of the second solution with a clean dropper and look for a colour change or solid.
- Record the colour of any precipitate, then repeat for each pair in the table.
- Rinse the droppers between solutions so the solutions do not mix.
Results
Sample results from Kofi’s group:
| Solution 1 | Solution 2 | Observation |
|---|---|---|
| Copper(II) sulfate | Sodium hydroxide | pale blue precipitate |
| Iron(III) chloride | Sodium hydroxide | red-brown precipitate |
| Magnesium sulfate | Sodium hydroxide | white precipitate |
| Calcium chloride | Sodium carbonate | white precipitate |
| Copper(II) sulfate | Iron(III) chloride | no change, mixed solution stays green-brown |
Analysis questions
Question 1 Formulae of the precipitates
Use ion charges to write the formula of each precipitate.Question 2 Copper equation
Write the balanced equation with state symbols for copper(II) sulfate and sodium hydroxide.Question 3 Iron ionic equation
Write the full equation for iron(III) chloride and sodium hydroxide, then the ionic equation.Question 4 Spectator ions
Name the spectator ions in the magnesium sulfate and sodium hydroxide reaction and write the ionic equation.Question 5 No reaction
Explain why copper(II) sulfate and iron(III) chloride gave no precipitate.Question 6 Identify an unknown
An unknown solution gives a red-brown precipitate with sodium hydroxide. Identify the metal ion and the precipitate.Question 7 Improving reliability
Suggest two ways to make the observations clearer and more reliable.
