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Qualitative tests are used to identify ions - Edexcel - GCSE Chemistry - Question 6 - 2016 - Paper 1
Question 6
Qualitative tests are used to identify ions. (a) A student carries out a flame test on an unknown solid. A red flame is seen. The student concludes that the solid i... show full transcript
Worked Solution & Example Answer:Qualitative tests are used to identify ions - Edexcel - GCSE Chemistry - Question 6 - 2016 - Paper 1
Step 1
Explain why this conclusion is not justified.
Answer
The conclusion that the solid is lithium carbonate based solely on the appearance of a red flame is not justified because multiple substances can produce similar flame colors. It is essential to conduct further tests to confirm the identification of the solid, as the red flame could originate from other sources such as strontium or certain organic compounds.
Step 2
Step 3
Why is it necessary to add dilute nitric acid in this test?
Answer
B Nitrate ions are needed for the test to work. Dilute nitric acid ensures that any carbonate ions or other interfering anions are neutralized, allowing the formation of a clear precipitate with silver nitrate when chloride ions are present.
Step 4
Step 5
Describe the test when sodium hydroxide solution is added to each of the solutions.
Answer
When sodium hydroxide solution is added to a solution containing iron(II) ions, a green precipitate of iron(II) hydroxide forms. In contrast, when added to a solution containing iron(III) ions, a reddish-brown precipitate of iron(III) hydroxide appears. This difference in color helps distinguish between the two types of iron ions.