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Complete the sentence by putting a cross (X) in the box next to your answer - Edexcel - GCSE Chemistry - Question 6 - 2017 - Paper 1
Question 6
Complete the sentence by putting a cross (X) in the box next to your answer. Sodium hydroxide solution is often used to test for ions in solution. When sodium hydr... show full transcript
Worked Solution & Example Answer:Complete the sentence by putting a cross (X) in the box next to your answer - Edexcel - GCSE Chemistry - Question 6 - 2017 - Paper 1
Step 1
Complete the sentence by putting a cross (X) in the box next to your answer.
Answer
The only correct answer is C.
A is not correct because if a green precipitate is formed when sodium hydroxide is added to a solution, it shows the solution contains iron(II) ions, not sodium ions.
B is not correct because if a green precipitate is formed, it indicates that it is not potassium ions present.
C is correct; the formation of a green precipitate indicates the presence of iron(II) ions, Fe²⁺.
D is irrelevant as it pertains to iron(III), which is not suggested by the green precipitate.
(b) The reason why it is not correct to state that the solution contains calcium ions is because aluminum ions can also produce a white precipitate when sodium hydroxide solution is added, which then disappears upon the addition of excess sodium hydroxide. This means the solution could contain aluminum ions instead.