Question

State the reason why ?

i. carbon is not used to reduce the oxides of sodium or aluminium.

ii. an iron strip is dipped in a blue copper sulphate solution turns the blue solution pale green.

iii. metals replace hydrogen from acids whereas non-metals do not.

iv. calcium does not occur free in nature.

v. zinc is used in the galvanisation of iron and not the copper.​

Answer 1

Solution :

(i) Both sodium and aluminium are stronger reducing agents than carbon. Therefore, carbon is not in a position to reduce the oxides of these metals to the metallic form. <br> (b) Iron displaces copper from copper sulphate solution to form iron sulphate which imparts pale green colour to it. <br> (iii) Calcium (Ca) is a reactive metal and is placed high in the activity series. It therefore, does not exist in free state also called native state. <br> (iv) Zinc is placed above iron in the activity series. When deposited over its surface (galvanisation), zinc gets corroded and not iron. But copper is placed below iron and therefore, does not participate the corrosion. In this case, iron is corroded or rusted.

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Answer 2

Answer :-

i. Carbon cannot reduce the oxides of reactive metals like sodium or aluminium. This is beacuse sodium & aluminium have a great affinity for oxygen (urge for combining) than carbon and therefore oxides of such metals cannot be reduced by carbon.

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ii. When an iron strip is dipped in a blue copper sulphate solution, a displacement reaction takes place and iron metal displaces copper from copper sulphate solution. Hence, the colour of the solution changes to pale green due to the formation of iron sulphate solution.

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iii. Most metals have high ionisation energy. This means that metals easily loose electrons. So they can replace hydrogen from acids as these hydrogen ions will receive the electrons from these metals and form gaseous hydrogen. On the other hand, ionisation energy of non-metals is lower than that of hydrogen, hence, they cannot displace hydrogen from acids.

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iv. Calcium is higly reactive metal and hence, readily combines with oxygen or water vapour present in air to form various compounds. As a result, these metals are not found in their free state.

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v. According to the reactivity series, zinc metal is more reactive than iron. Hence, when zinc is coated on iron metal, it will get oxidised and attains a coating of zinc oxide which prevents rusting of iron. But, copper is less reactive than iron hence, it will not react with iron and does not form any oxide layer on it. Therefore, zinc is used in the galvanization of iron and not copper.