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Identification of ions by chemical and spectroscopic means
Study qualitative chemical tests for ions, including required practical methods, and compare them with instrumental analysis.
56
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaGcseChemistryChemical analysis
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56 objective pages available
Flame tests9 objectives
- Describe how flame tests can be used to identify some metal ions.
- Recall that lithium ions produce a crimson flame.
- Recall that sodium ions produce a yellow flame.
- Recall that potassium ions produce a lilac flame.
- Recall that calcium ions produce an orange-red flame.
- Recall that copper ions produce a green flame.
- Interpret flame colour observations to identify metal ions.
- Explain why flame tests are qualitative tests.
- Carry out flame tests safely using appropriate apparatus. (AT 8)
Metal hydroxide precipitate tests10 objectives
- Describe how sodium hydroxide solution can be used to test for some metal ions.
- Recall that aluminium ions form a white precipitate that dissolves in excess sodium hydroxide.
- Recall that calcium ions form a white precipitate with sodium hydroxide.
- Recall that magnesium ions form a white precipitate with sodium hydroxide.
- Recall that copper(II) ions form a blue precipitate with sodium hydroxide.
- Recall that iron(II) ions form a green precipitate with sodium hydroxide.
- Recall that iron(III) ions form a brown precipitate with sodium hydroxide.
- Interpret precipitate colours and solubility in excess sodium hydroxide to identify metal ions.
- Distinguish metal hydroxide precipitate tests from flame tests.
- Carry out metal ion tests using sodium hydroxide solution safely. (AT 8)
Carbonate ions7 objectives
- Describe the test for carbonate ions using dilute acid.
- Recall that carbonate ions react with dilute acid to produce carbon dioxide.
- Explain that carbon dioxide can be confirmed by bubbling the gas through limewater.
- Recall that limewater turns milky if carbon dioxide is produced.
- Interpret effervescence and limewater turning milky as evidence for carbonate ions.
- Distinguish the carbonate ion test from sulfate and halide ion tests.
- Carry out the carbonate ion test safely. (AT 8)
Sulfate ions6 objectives
- Describe the test for sulfate ions using barium chloride solution.
- Explain that the sample is acidified before adding barium chloride solution.
- Recall that sulfate ions produce a white precipitate of barium sulfate.
- Interpret a white precipitate with acidified barium chloride solution as evidence for sulfate ions.
- Distinguish the sulfate ion test from carbonate and halide ion tests.
- Carry out the sulfate ion test safely. (AT 8)
Halide ions8 objectives
- Describe the test for halide ions using silver nitrate solution.
- Explain that the sample is acidified with dilute nitric acid before adding silver nitrate solution.
- Recall that chloride ions produce a white precipitate.
- Recall that bromide ions produce a cream precipitate.
- Recall that iodide ions produce a yellow precipitate.
- Interpret precipitate colour after adding acidified silver nitrate solution to identify halide ions.
- Distinguish the halide ion test from carbonate and sulfate ion tests.
- Carry out the halide ion test safely. (AT 8)
Required practical: identifying ions8 objectives
- Use flame tests to identify metal ions in unknown compounds.
- Use sodium hydroxide solution to identify metal ions in unknown compounds.
- Use carbonate, sulfate and halide tests to identify negative ions in unknown compounds.
- Record observations accurately during ion identification tests.
- Use observations to make valid conclusions about the ions present.
- Plan a sequence of tests to identify ions in an unknown compound.
- Explain why positive ion tests and negative ion tests may both be needed to identify an ionic compound.
- Evaluate test results for consistency with expected observations. (AT 8; WS 2.2, 2.4)
Instrumental methods8 objectives
- Explain that instrumental methods can be used to detect and identify elements and compounds.
- Explain that instrumental methods are accurate, sensitive and rapid.
- Explain that instrumental methods are especially useful when the sample is very small.
- Compare instrumental methods with chemical tests in terms of speed, sensitivity and sample size.
- Describe flame emission spectroscopy as an example of an instrumental method.
- Explain that flame emission spectroscopy can identify metal ions from a line spectrum.
- Explain that the intensity of lines in flame emission spectroscopy can be used to measure concentration.
- Interpret information from instrumental analysis to identify substances.
Key terms
Flame testMetal ion identificationlithium ionflame testSodium Ion Flame TestFlame Colour ObservationPotassium ionCalcium Ion Flame TestFlame TestCopper Ion Flame TestFlame Test MethodologyQualitative test
Exam tips
- Master Flame Test Identification: Remember to memorize the flame colors produced by common metal ions: lithium (crimson), sodium (yellow), potassium (lilac), calcium (orange-red), and copper (green). Link your answer to Flame tests, and keep the test, observation, and conclusion distinct where qualitative analysis is involved.
- Remember Lithium's Flame Color: Remember to when preparing for your exam, memorize that lithium ions produce a crimson flame during flame tests. Link your answer to Flame tests, and keep the test, observation, and conclusion distinct where qualitative analysis is involved.
Common mistakes
- Confusing Flame Colors: To fix this, students should memorize the specific flame colors associated with each metal ion, such as lithium for crimson, sodium for yellow, and potassium for lilac.
- Confusing Flame Colors: Remember that lithium ions specifically produce a crimson flame, while sodium ions produce a yellow flame. Use visual aids or color charts to help differentiate between the two.
Practice preview
- Which statement would earn credit for Describe how flame tests can be used to identify some metal ions.?
- For Identification of ions by chemical and spectroscopic means, which option uses the correct Chemical analysis evidence for flame test?
- Which answer avoids confusing flame test with another qualitative analysis result?
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