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.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The conclusion that the solid is lithium carbonate is not justified because a red flame can be produced by other metal ions, such as strontium. Therefore, the presence of a red flame alone is insufficient to confirm the identity of the compound.
Step 2
Give the name and formula of the substance.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The name of the substance is sodium chloride, and its formula is NaCl.
Step 3
Why is it necessary to add dilute nitric acid in this test?
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
It is necessary to add dilute nitric acid to eliminate any carbonate ions that could react with silver nitrate. This ensures that any precipitate formed is solely due to the presence of chloride ions.
Step 4
Describe the test to show the gas is ammonia.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To test for ammonia gas, you can use a damp red litmus paper. When ammonia is present, it will turn the red litmus paper blue, indicating the basic nature of ammonia.
Step 5
Describe the test when sodium hydroxide solution is added to each of these.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
When sodium hydroxide solution is added to iron(II) ions, a green precipitate of iron(II) hydroxide, Fe(OH)₂, is formed. In contrast, when added to iron(III) ions, a reddish-brown precipitate of iron(III) hydroxide, Fe(OH)₃, is formed. This difference helps distinguish between the two types of iron ions.
