AQA GCSE Chemistry
AQA GCSE Chemistry 4.8.3 Identification of Ions by Chemical and Spectroscopic Means Exam Questions
Free AQA GCSE Chemistry exam questions for 4.8.3 Identification of Ions by Chemical and Spectroscopic Means, with a mark scheme for every pack. Covers flame tests, metal hydroxide precipitates, tests for carbonates, halides and sulfates, instrumental methods and flame emission spectroscopy.
4.8.3 Identification of Ions by Chemical and Spectroscopic Means exam questions
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About AQA GCSE Chemistry 4.8.3 Identification of Ions by Chemical and Spectroscopic Means
AQA GCSE Chemistry 4.8.3 is separate Chemistry only content on identifying the ions in an unknown compound. You learn flame tests for metal ions, the sodium hydroxide test for metal ions that form coloured or white precipitates, and the tests for carbonate, halide and sulfate ions. The required practical asks you to use these tests to identify the ions in unknown single ionic compounds. You also compare these with instrumental methods such as flame emission spectroscopy. It is assessed on Paper 2 and links to transition metal colours in 4.1.3. Expect questions that ask you to identify a compound from a set of results.
What you need to know
- Flame tests Lithium: crimson; sodium: yellow; potassium: lilac; calcium: orange-red; copper: green. A mixture of ions may mask some colours.
- Sodium hydroxide test Add a few drops of sodium hydroxide solution. Aluminium, calcium and magnesium give white precipitates; only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide. Copper(II) gives blue, iron(II) gives green and iron(III) gives brown precipitates.
- Carbonates Add dilute acid: effervescence, and the carbon dioxide produced turns limewater milky.
- Halides Add dilute nitric acid then silver nitrate solution. Chloride gives a white precipitate, bromide a cream precipitate and iodide a yellow precipitate.
- Sulfates Add dilute hydrochloric acid then barium chloride solution. A white precipitate shows sulfate ions.
- Instrumental methods Instrumental methods are accurate, sensitive and rapid. Flame emission spectroscopy passes light from a flame through a spectroscope to give a line spectrum that identifies metal ions and, by comparing intensity, their concentration.
Common mistakes in 4.8.3 Identification of Ions by Chemical and Spectroscopic Means
- Adding hydrochloric acid before silver nitrate in the halide test. The chloride ions would give a false positive; use nitric acid.
- Adding sulfuric acid before barium chloride in the sulfate test. The added sulfate ions would always give a precipitate; use hydrochloric acid.
- Confusing iron(II) and iron(III) colours. Iron(II) hydroxide is green; iron(III) hydroxide is brown.
- Saying calcium and magnesium can be told apart with sodium hydroxide. Both give white precipitates that do not dissolve in excess; use a flame test (calcium is orange-red, magnesium gives no colour).
- Describing results as a 'blue solution' when the test gives a blue precipitate (solid).
Try three 4.8.3 Identification of Ions by Chemical and Spectroscopic Means exam-style questions
1. A student adds sodium hydroxide solution to a solution of an unknown compound and a blue precipitate forms. Identify the metal ion and write an ionic equation. (2 marks)
Show the mark scheme answer
Copper(II), Cu2+; Cu2+ + 2OH- → Cu(OH)2.
2. Describe how to test a solution for bromide ions. Give the result. (3 marks)
Show the mark scheme answer
Add dilute nitric acid; then silver nitrate solution; cream precipitate.
3. A white solid gives a yellow flame and forms a white precipitate with dilute hydrochloric acid and barium chloride solution. Identify the compound. (2 marks)
Show the mark scheme answer
Sodium (from yellow flame); sulfate (white precipitate with barium chloride); sodium sulfate.
4.8.3 Identification of Ions by Chemical and Spectroscopic Means FAQs
What does AQA GCSE Chemistry 4.8.3 cover?
It covers flame tests, sodium hydroxide precipitate tests for metal ions, tests for carbonate, halide and sulfate ions, and instrumental methods including flame emission spectroscopy.
Is 4.8.3 on combined science?
No. 4.8.3 is separate Chemistry only content assessed on Paper 2, and it includes the identifying ions required practical.
How do I learn all the ion test results?
Make a table with the ion, reagents and result, and test yourself until you can fill it in from memory. Pay attention to which acid is added first in each test and why.
