Chemical tests: aqueous ions (including zinc)
Lesson details
Learning outcome
I can perform and interpret sodium hydroxide precipitate tests for metal ions and other tests for identifying ammonium, carbonate, sulfate, and halide ions.
Key learning points
- Some metal ions form coloured precipitates in a reaction with sodium hydroxide solution.
- Ammonium ions can be identified by heating with NaOH and using damp red litmus paper, which turns blue if positive.
- A dilute acid is usually added before testing for carbonates, sulfates or halides to avoid false positives.
- Halide ions produce different coloured precipitates when silver nitrate is added to a solution containing them.
- A white precipitate is formed when barium chloride is added to an acidified solution containing sulfate ions.
Keywords
Precipitate - An insoluble solid formed when two solutions react together.
Ion - An ion is an atom or group of atoms with a positive or negative charge due to the loss or gain of electrons.
Cation - A positively charged ion.
Anion - A negatively charged ion.
Common misconception
All white precipitates in chemical tests indicate the presence of the same ion without the need for further testing.
Explain that white precipitates can indicate different ions depending on the test. For instance, barium sulfate indicates sulfate ions, silver chloride indicates chloride ions, and sodium hydroxide tests distinguish between cations.
Teacher tip
Emphasise the importance of following proper procedures for each specific test, including using the correct reagents and conditions, to avoid confusion and ensure accurate results.
Equipment
NaCl, CaSO₄, Na₂SO₄, BaCl₂, HCl, AgNO₃, HNO₃, pipettes, test tubes, test tube racks, limewater, delivery tubes, bungs, boiling tubes
Content guidance
Risk assessment required - chemicals
Risk assessment required - equipment
Supervision
Adult supervision required
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which particle does an atom lose or gain one or more of to form an ion?
Q2.What does litmus paper indicate?
Q3.What is the charge of a cation?
Q4.Which of the following is a common laboratory acid?
Q5.Which of the following are basic laboratory techniques?
Q6.What does a basic understanding of chemical reactions include?
Assessment exit quiz
6 Questions
Q1.What colour precipitate does copper(II) form with sodium hydroxide?
Q2.Which gas is released when ammonium ions are heated with sodium hydroxide?
Q3.What colour does damp red litmus paper turn in the presence of ammonia gas?
Q4.What colour precipitate is formed when silver nitrate is added to a solution containing chloride ions?
Q5.Why is dilute nitric acid added before testing for halides?
Q6.What precipitate is formed when barium chloride is added to an acidified solution containing sulfate ions?
To help you plan your 11 chemistry lesson on: Chemical tests: aqueous ions (including zinc), download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 11 chemistry lesson on: Chemical tests: aqueous ions (including zinc), download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
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