Consider the following statements regarding burning of magnesium ribbon in air : 1. White powder of MgO is formed. 2. It is an example of combustion reaction. 3. Heat and light are produced. Which of the statements given above are correct?
- A.1 and 2 only
- B.1 and 3 only
- C.2 and 3 only
- D.1, 2 and 3
Correct answer
Explanation
The correct answer is D, 1, 2 and 3. Magnesium ribbon burns in air with a dazzling white flame, giving off heat and light and leaving a white powder of magnesium oxide.
The reaction is 2Mg + O₂ → 2MgO. Magnesium combines with oxygen of the air, so it is a combustion reaction, and it is also a combination and an oxidation reaction. It is strongly exothermic: the heat and the bright white light are why magnesium was once used in photographers' flash powder and is still used in fireworks and flares. The white ash is magnesium oxide, a basic oxide that turns red litmus blue when dissolved in water.
A is wrong: it leaves out statement 3, though heat and light are clearly produced.
B is wrong: it leaves out statement 2, but burning in oxygen is combustion.
C is wrong: it leaves out statement 1, but the product is indeed white MgO powder.
Exam tip: magnesium burns with a dazzling white flame to give MgO, a basic oxide; clean the ribbon with sandpaper first to remove the oxide layer.
Practice Questions
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