CIE iGCSE Co-Ordinated Science C7.2 Oxides Exam Style Questions Paper 1
▶️ Answer/Explanation
Oxides can be classified as acidic or basic based on the metallic or non-metallic character of the element forming the oxide:
- Metals form basic oxides. These oxides react with acids to form a salt and water (neutralisation). For example, magnesium oxide (MgO) is a basic oxide.
- Non-metals form acidic oxides. These oxides react with bases to form a salt and water. For example, sulfur dioxide (SO\(_2\)) and sulfur trioxide (SO\(_3\)) are acidic oxides.
Magnesium is a metal, so it forms a basic oxide. Sulfur is a non-metal, so it forms an acidic oxide. Therefore, magnesium = basic and sulfur = acidic, which matches row C.
✅ Answer: (C)
▶️ Answer/Explanation
Calcium and lithium are metals, and metal oxides are generally basic, so calcium oxide and lithium oxide are basic, not acidic.
Nitrogen and phosphorus are non-metals, and non-metal oxides are generally acidic.
So the acidic oxides are nitrogen oxide and phosphorus oxide, which are oxides 3 and 4.
✅ Answer: (D)
Nitrogen and phosphorus are non-metals, and non-metal oxides are generally acidic.
So the acidic oxides are nitrogen oxide and phosphorus oxide, which are oxides 3 and 4.
✅ Answer: (D)
▶️ Answer/Explanation
Basic oxides are formed by metals; calcium oxide is the oxide of the metal calcium.
Carbon dioxide, nitrogen dioxide, and sulfur dioxide are all oxides of non-metals, making them acidic oxides.
Calcium oxide reacts with acids to form a salt and water, confirming its basic character.
✅ Answer: (A)
Carbon dioxide, nitrogen dioxide, and sulfur dioxide are all oxides of non-metals, making them acidic oxides.
Calcium oxide reacts with acids to form a salt and water, confirming its basic character.
✅ Answer: (A)
▶️ Answer/Explanation
Potassium is a metal, so potassium oxide is a basic oxide, not an acidic oxide as listed.
Sulfur dioxide is a non-metal oxide, so it is an acidic oxide, not a basic oxide as listed.
Carbon dioxide is correctly acidic and sodium oxide is correctly basic, so only potassium oxide and sulfur dioxide are misplaced.
✅ Answer: (B)
Sulfur dioxide is a non-metal oxide, so it is an acidic oxide, not a basic oxide as listed.
Carbon dioxide is correctly acidic and sodium oxide is correctly basic, so only potassium oxide and sulfur dioxide are misplaced.
✅ Answer: (B)
Question
Which substance is classified as an acidic oxide?
(A calcium oxide
(B) carbon dioxide
(C) lithium oxide
(D) sodium oxide
▶️Answer/Explanation
Ans: B