Qualitative tests are used to identify ions in compounds. (a) Solid X contains two ions. The tests for these ions and their results are shown in Figure 10. test result flame test on solid X red-orange flame dilute nitric acid is added to an aqueous solution of X, followed by silver nitrate solution Figure 10 Use the information in Figure 10 to name the cation and the anion in solid X. name of cation name of anion (b) Another solid, Y, also contains two ions. a test was carried out on solid Y. A few drops of sodium hydroxide solution were added to a solution of solid Y. A white precipitate formed. (i) Give the reason why this test does not identify the cation in solid Y. (ii) Give the reason why this test does not identify the anion in solid Y. (c) Instrumental methods are often used for analysis. Give a reason why instrumental analysis may be better than other methods of analysis. (d) Iron(II) sulfate solution reacts with sodium hydroxide solution to form a pale green precipitate of iron(II) hydroxide, Fe(OH)₂. (i) Write the ionic equation for this reaction. (ii) The green iron(II) hydroxide precipitate gradually turns brown when exposed to air. Explain this observation.

GCSE Edexcel Chemistry Tests for anions: Qualitative tests are used to id

Qualitative tests are used to identify ions in compounds - Edexcel - GCSE Chemistry - Question 8 - 2018 - Paper 1

Question 8

Qualitative tests are used to identify ions in compounds. (a) Solid X contains two ions. The tests for these ions and their results are shown in Figure 10. test... show full transcript

Worked Solution & Example Answer:Qualitative tests are used to identify ions in compounds - Edexcel - GCSE Chemistry - Question 8 - 2018 - Paper 1

Step 1

Use the information in Figure 10 to name the cation and the anion in solid X.

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Answer

The cation in solid X can be identified as calcium ( ext{Ca}^{2+}) due to the red-orange flame test, which indicates the presence of calcium ions. The anion can be identified as chloride ( ext{Cl}^-) since the addition of dilute nitric acid followed by silver nitrate produces a white precipitate, indicating the presence of chloride ions.

Step 2

Give the reason why this test does not identify the cation in solid Y.

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Answer

The test does not identify the cation in solid Y because sodium hydroxide can produce a white precipitate with multiple cations. Therefore, the formation of a white precipitate does not uniquely indicate the presence of any specific cation.

Step 3

Give the reason why this test does not identify the anion in solid Y.

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Answer

The presence of a white precipitate could result from several anions, so this test does not uniquely identify any specific anion in solid Y.

Step 4

Give a reason why instrumental analysis may be better than other methods of analysis.

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Answer

Instrumental analysis may be better because it improves sensitivity and accuracy of results, allowing for more precise identification and quantification of ions than traditional methods.

Step 5

Write the ionic equation for this reaction.

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Answer

The ionic equation for the reaction of iron(II) sulfate with sodium hydroxide can be written as:

ightarrow ext{Fe(OH)}_2 (s)$$

Step 6

Explain this observation.

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Answer

The green iron(II) hydroxide precipitate gradually turns brown upon exposure to air because it is oxidized to iron(III) hydroxide ext{Fe(OH)}_3, which has a brown coloration. This oxidation occurs as iron(II) ions are converted to iron(III) ions on exposure to oxygen in the air.

Qualitative tests are used to identify ions in compounds - Edexcel - GCSE Chemistry - Question 8 - 2018 - Paper 1

Worked Solution & Example Answer:Qualitative tests are used to identify ions in compounds - Edexcel - GCSE Chemistry - Question 8 - 2018 - Paper 1

Use the information in Figure 10 to name the cation and the anion in solid X.

Give the reason why this test does not identify the cation in solid Y.

Give the reason why this test does not identify the anion in solid Y.

Give a reason why instrumental analysis may be better than other methods of analysis.

Write the ionic equation for this reaction.

Explain this observation.

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