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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, iron(II), Fe2+. This is because a green precipitate indicates the presence of iron(II) ions in the solution. If sodium or potassium were present, a different color would have been observed.
Step 2
Give a reason, using the information in the table, why it is not correct to say that the solution contains calcium ions.
Answer
It is not correct to say that the solution contains calcium ions because, according to the table, when sodium hydroxide is added to calcium ions, a white precipitate forms but remains even with excess sodium hydroxide. In contrast, the white precipitate formed from aluminum ions disappears when excess sodium hydroxide is added. Thus, if only a white precipitate forms without disappearing, it can only indicate aluminum, not calcium.