Answer the questions.[Che-3M]

Question 13 Marks

A solution of a substance 'X' is used for whitewashing i. Name the substance 'X' and writes its formula. ii. Write the reaction of the substance 'X' named in (i) above with water.

Answer

i. The substance whose solution in water is used for white washing is calcium oxide. Its formula is $\mathbf{C a O}$.
ii. When quicklime is mixed with water, the following reaction takes place:
$\underset{\substack{\text { Calcium } \$\text { QuickL } \mathrm{Im} e)}}{\mathrm{CaO}(\mathrm{s})}+\underset{\text { water }}{\mathrm{H}_2 \mathrm{O}(\mathrm{l})} \rightarrow \underset{\substack{\text { Calcium hydroxide } \\ \text { (Sleked lime) }}}{\mathrm{Ca}(\mathrm{OH})_2(\mathrm{aq})}+$ Heat

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Question 23 Marks

In a chemistry laboratory, students were instructed to set up three experiments, details of which are given below:

Experiment No.	Set up details
1.	2 iron nails in a cork capped test tube + Tap water immersing the nails +
2.	2 iron nails in a cork capped test tube + Boiled water immersing the nails + Oil on top of water layer.
3.	2 iron nails In a cork capped test tube + Cotton wool on top of the iron nails + Granules of calcium chloride on cotton wool.

Indicate the changes observed in the nails kept in all the three setups, with reasons.

Answer

Test tube 1 : Iron nails would get rusted that is corroded as they are exposed to moisture and air.
Test tube 2 : Iron nails won't get rusted as they are exposed to water that is devoid of oxygen due to boiling and further the layer of oil is not letting oxygen come into contact with the water in which nails are immersed.
Test tube 3 : Iron nails won't get rusted or corroded because they are not exposed to moisture and air.

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Question 33 Marks

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
i. In thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
ii. Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.

Answer

i. $\underset{\text { From }[\text { ITI }) \text { maxid: }}{\mathrm{Fe}_2 \mathrm{O}_3(\mathrm{~s})}+\underset{\text { Aluminimum }}{2 \mathrm{Al}(\mathrm{s})} \xrightarrow{\Delta} \underset{\text { Mattes inon }}{2 \mathrm{Fe}(\mathrm{l})}+\underset{\text { Shuminium prolfr }}{\mathrm{Al}_2 \mathrm{O}_{3(\mathrm{~s})}}$
The thermite reaction is a displacement reaction.
ii. $\underset{\text { Magnesium }}{3 M g(s)}+\underset{\text { Nitrogen }}{N_2(g)} \xrightarrow{\Delta} \underset{\text { Magnesium nitride }}{M g_3 N_2(s)}$
The formation of magnesium nitride as above is a combination reaction.

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