Consider the following pairs : Chemical Reaction — Type of Chemical Reaction I. Fe(s) + CuSO₄(aq.) → FeSO₄(aq.) + Cu(s) — Displacement reaction II. Na₂SO₄(aq.) + BaCl₂(aq.) → BaSO₄(s) + 2NaCl(aq.) — Double displacement reaction III. Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g) — Redox reaction IV. 2KClO₃(s) → 2KCl(s) + 3O₂(g) — Thermal decomposition reaction How many of the pairs given above are correctly matched?
- A.One
- B.Two
- C.Three
- D.All four
Correct answer
Explanation
The correct answer is D, All four. Each reaction is labelled with its correct type, so every pair is matched correctly.
In I, iron is more reactive than copper and pushes it out of copper sulphate, a displacement reaction. In II, sodium sulphate and barium chloride exchange ions and white barium sulphate settles out, a double displacement (precipitation) reaction. In III, iron oxide loses oxygen and is reduced while carbon monoxide gains oxygen and is oxidised, so it is a redox reaction; this is how iron is extracted in a blast furnace. In IV, potassium chlorate breaks down on heating into potassium chloride and oxygen, a thermal decomposition.
A is wrong because more than one pair is correct.
B is wrong because all four pairs, not just two, are correct.
C is wrong because not one of the four pairs is mismatched.
Exam tip: one element replaces another = displacement; two compounds swap ions = double displacement; oxygen gained and lost together = redox; heat breaks one compound = thermal decomposition.
Practice Questions
View allHow is carbon black obtained ?
- A.By heating wood at high temperature in absence of air
- B.By heating coal at high temperature in absence of air
- C.By burning hydrocarbons in a limited supply of air
- D.By heating coal at high temperature in presence of air
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When natural gas or heavy oil burns with too little air, the carbon cannot all turn into carbon dioxide and separates as a very fine black soot, which is collected as carbon black.
Read the full explanation →The equivalent weight of oxalic acid in C₂H₂O₄·2H₂O is
- A.45
- B.63
- C.90
- D.126
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Hydrated oxalic acid has a molar mass of 126 and is a dibasic acid, so its equivalent weight is 126 ÷ 2 = 63.
Read the full explanation →Which one of the following is not a monatomic element?
- A.Copper
- B.Helium
- C.Iodine
- D.Barium
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Iodine exists as diatomic molecules, I₂, in which two iodine atoms share a pair of electrons; so its atomicity is two, not one.
Read the full explanation →Which one of the following reactions does not result in the evolution of hydrogen gas ?
- A.Reaction of zinc metal with dilute sulphuric acid solution
- B.Mixing water to Plaster of Paris
- C.Heating zinc metal with sodium hydroxide solution
- D.Reaction of potassium metal with water
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Here water only combines with calcium sulphate hemihydrate to form gypsum; no gas is given off and the paste simply sets hard.
Read the full explanation →Which one of the following statements is not correct?
- A.Most carbon compounds are good conductors of electricity.
- B.Bonding in organic compounds is covalent.
- C.Graphite is used as a lubricant.
- D.Diamond is an allotrope of carbon.
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Most carbon compounds are poor conductors of electricity, because their atoms are joined by covalent bonds and they do not form ions or free electrons that could carry a current.
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