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7. (a) Qualitative tests are carried out on ionic substances to identify the ions present in the substances - Edexcel - GCSE Chemistry - Question 7 - 2019 - Paper 1
Question 7
7. (a) Qualitative tests are carried out on ionic substances to identify the ions present in the substances. (i) Explain why the test for a given ion must be unique... show full transcript
Worked Solution & Example Answer:7. (a) Qualitative tests are carried out on ionic substances to identify the ions present in the substances - Edexcel - GCSE Chemistry - Question 7 - 2019 - Paper 1
Step 1
Explain why the test for a given ion must be unique to that ion.
Answer
A test for a given ion must be unique to that ion to ensure that the identification process is accurate and reliable. If a test were not unique, there could be confusion and misidentification of ions. Specificity in testing helps to avoid false positives, ensuring that the observed result directly correlates to the intended ion without interference from other ions.
Step 2
Step 3
Step 4
Describe tests to show the presence of each of these metal ions.
Answer
To test for sodium ions, flame test can be performed; a yellow flame indicates the presence of sodium. For potassium ions, the flame test will show a lilac or light purple flame. Calcium ions can be tested using a flame test that gives an orange-red flame. Lastly, aluminum ions can be detected by adding sodium hydroxide, which forms a white precipitate that dissolves in excess, indicating the presence of aluminum.