CIE iGCSE Co-Ordinated Science C12.5 Identification of ions and gases Exam Style Questions Paper 1
Question
The results of two tests on substance X are listed.
1. A lilac flame is produced in a flame test.
2. A gas which turns damp red litmus blue is produced when X is heated with aluminium powder and aqueous sodium hydroxide.
What is X?
A. potassium nitrate
B. potassium sulfate
C. sodium nitrate
D. sodium sulfate
▶️Answer/Explanation
Answer: A
Explanation: The lilac flame indicates the presence of potassium, and the gas that turns damp red litmus blue is ammonia, which is produced when nitrates are heated with aluminium powder and sodium hydroxide. Therefore, X is potassium nitrate.
Question
Three different tests are carried out on an aqueous solution of substance X. The results are shown.
| Test | Result |
|---|---|
| Add a few drops of aqueous sodium hydroxide | Blue precipitate |
| Add acidified aqueous silver nitrate | No precipitate |
| Add acidified aqueous barium nitrate | White precipitate |
What is X?
A. copper(II) chloride
B. copper(II) sulfate
C. iron(II) chloride
D. iron(II) sulfate
▶️Answer/Explanation
Answer: B
Explanation: The blue precipitate with sodium hydroxide indicates the presence of copper(II) ions. The white precipitate with barium nitrate indicates the presence of sulfate ions. Therefore, X is copper(II) sulfate.
Question
A white solid X dissolves in dilute hydrochloric acid. A gas is produced which turns limewater milky. A flame test is carried out on solid X and produces a red-colored flame. What is X?
A) lithium carbonate
B) lithium chloride
C) potassium carbonate
D) potassium chloride
▶️Answer/Explanation
Answer: A) lithium carbonate
Explanation: The gas produced (CO₂) turns limewater milky, indicating the presence of a carbonate. The red flame test indicates the presence of lithium.
Question
Which test and its result identifies aqueous bromide ions?
A adding acidified aqueous silver nitrate forming a cream precipitate
B adding acidified aqueous silver nitrate forming a white precipitate
C adding aluminium foil and heating with sodium hydroxide forming a gas that turns red litmus
paper blue
D adding dilute acid forming a gas that produces a white precipitate when bubbled through
limewater
▶️Answer/Explanation
Ans :B
Question
Which row shows the flame test colours for lithium and sodium?
▶️Answer/Explanation
Ans : D
Question
A piece of damp blue litmus paper is put in a test-tube of a gas. The litmus paper turns red and then changes to white.
What is the gas?
(A) ammonia
(B) carbon dioxide
(C) chlorine
(D) oxygen
▶️Answer/Explanation
Ans: C
Question
Substance X is mixed with aqueous sodium hydroxide.
A green precipitate is produced.
Which metal ion is present in X?
(A) Cu$^{2+}$
(B) Fe$^{2+}$
(C) Fe$^{3+}$
(D) Zn$^{2+}$
▶️Answer/Explanation
Ans : B
Question
What is used to test for the presence of carbon dioxide?
(A) Benedict’s solution
(B) ethanol
(C) iodine solution
(D) limewater
▶Answer/Explanation
Ans : D
Question
White solid X reacts with dilute hydrochloric acid. A gas is produced which turns limewater milky. A flame test is done on solid X and produces a red coloured flame.
What is X?
(A) lithium carbonate
(B) lithium chloride
(C) potassium carbonate
(D) potassium chloride
▶️Answer/Explanation
Ans: A
Question
Which chemical test does not produce a precipitate?
A. carbon dioxide and limewater
B. carbonate ions and dilute hydrochloric acid
C. chloride ions and aqueous silver nitrate
D. copper(II) ions and aqueous sodium hydroxide
▶️Answer/Explanation
Answer: B. carbonate ions and dilute hydrochloric acid
Explanation: Carbonate ions react with dilute hydrochloric acid to produce carbon dioxide gas, not a precipitate.
Question
What test is used to test for chlorine?
A. damp litmus paper
B. glowing splint
C. lighted splint
D. limewater
▶️Answer/Explanation
Answer: A. damp litmus paper
Explanation: Chlorine gas bleaches damp litmus paper, turning it white. This is a standard test for chlorine.
Question
Which test is used to identify sulfate ions?
A. aqueous barium ions under acidic conditions
B. aqueous silver nitrate under acidic conditions
C. dilute acid and then limewater
D. reduction with aluminium
▶️Answer/Explanation
Answer: A
Explanation: Sulfate ions (SO42-) can be identified by adding aqueous barium ions (Ba2+) under acidic conditions. A white precipitate of barium sulfate (BaSO4) forms, which is insoluble in acids.