Question

Read the passage and answer the following question:

Clean a magnesium ribbon about 2 cm long by rubbing it with a sand paper.

Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the

ash so formed in a watch glass. Burn the magnesium ribbon keeping it as far as

possible from our eye. What do you observe?

i. What is the symbol of magnesium?

ii. Why the magnesium ribbon is rubbed with a sand paper?

iii. Name the ash formed as a result of burning of magnesium ribbon?

iv. Name the elements present in the ash formed?

v. Write its balanced equation and the type of reaction?​

Answer 1

1) The symbol of magnesium is Mg.  

2) The magnesium ribbon is rubbed with a sand paper because magnesium forms magnesium oxide on reacting with oxygen present in the air.  

3) MgO  

4) Mg and MgO  

5) Mg+ O₂  ==≻ MgO

Answer 2

The following questions are answered below:

1. The symbol of magnesium is Mg.

2. The magnesium ribbon is rubbed with sandpaper before burning because-

• There may be a layer of magnesium oxide formed and accumulated on the surface, which may inhibit the reaction of magnesium with oxygen.
• Besides this, other impurities, if present can also be removed by rubbing with sandpaper.

3. The name of the ash formed as a result of burning of magnesium ribbon is - magnesium oxide.

• Upon burning in air, magnesium reacts with oxygen with a dazzling white flame and magnesium oxide is formed.
• This magnesium oxide is in white powder form.

• Hence, it is obtained as ash.

4. The elements present in the ash formed are named below: Magnesium oxide.

• Magnesium will burn to form magnesium oxide.
• Magnesium is greyish-white in colour while magnesium oxide is white in colour.
• In the ash, only magnesium oxide will be present.

5. The balanced equation and the type of reaction are written below:

Balanced equation -

$2Mg(s)+O_{2} \rightarrow 2MgO$

Type of reaction - Combination reaction

• As we can see, here there are two reactants, magnesium and oxygen. Both these reactants combine to form magnesium oxide, a single product. Thus, this is a combination reaction.
• And like most of the combination reactions, energy is liberated in this reaction too.