Question

State reason for the following :

(i) A tarnished copper vessel begins to shine again when rubbed with lemon.

(ii) all alkalies are bases but all bases are not alkalies
(iii) use of a mild base like baking soda on the honey - bee stung area gives relief.

Answer 1

Here's your answer:-

(I) Copper vessel is tarnished due to copper oxide layer formed on its surface. Copper oxide is basic in nature. Whereas, lemon is acidic in nature. Thus, on rubbing the vessel with lemon, copper oxide reacts with the acid to form a salt which is washed away with water.

(II) A base is a substance that reacts with acids and neutralize them. Alkalis are bases which are soluble in water. However, all bases are not soluble in water. For example, copper oxide is not soluble in water.

(III) Baking soda is a mild base and when applied on the stung area, it neutralises the acidic liquid injected by the bee. Thus rubbing the stung area with mild base gives relief.

Hope this answer helps you.

Answer 2

The reasons for the following are given below:

Explanation:

(i) A tarnished copper vessel begins to shine again when rubbed with lemon because

• Lemon is acidic in nature which dissolves the green coating of basic copper carbonate present on the surface of a tarnished copper vessel and makes it shiny again.
• The citric acid present in the lemon neutralizes the basic copper carbonate and dissolves the layer.

(ii) All alkalies are bases, but all bases are not alkali Because

• Alkalies are bases that dissolve in water, while all alkalies are basic in nature, but all bases are not soluble in water. Hence, all bases are not alkali.

(iii) Use of mild base like baking soda on the honey bee stung area gives relief because

• Bee-sting is acidic in nature which causes pain, redness and irritation.
• With the use of a mild base, such as, baking soda on the stung area, which helps in getting relief because baking soda is basic in nature and neutralizes the acid present in bee stung.

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