Give reasons :
(a) Sodium metal is kept in Kerosene oil
(b) Platinum, gold, silver are used to make jewellery.
(c) Tarnished copper vessels are cleaned.
CBSE Class X Science SA 2 (3 Marks)
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(a) Na, K, Li etc. are very reactive so these metals reacts vigorously with atmospheric oxygen to
form oxides. Storing them in oil prevents their oxidation.
(b) Platinum, gold and silver are least reactive i.e., they are noble metals, so they are not corroded by air and water easily.
(c) Copper vessels get tarnished by reacting with air and water, due to which a layer is formed, which mainly contains black copper oxide and green copper hydroxide, which is basic in nature. The citric acid in lemon dissolve this layer and washes off easily.
(b) Platinum, gold and silver are least reactive i.e., they are noble metals, so they are not corroded by air and water easily.
(c) Copper vessels get tarnished by reacting with air and water, due to which a layer is formed, which mainly contains black copper oxide and green copper hydroxide, which is basic in nature. The citric acid in lemon dissolve this layer and washes off easily.
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Answer:
(a) Na, K, Li etc. are very reactive so these metals reacts vigorously with atmospheric oxygen to form oxides. Storing them in oil prevents their oxidation.
(b) Platinum, gold and silver are least reactive i.e., they are noble metals, so they are not corroded by air and water easily.
(c) Copper vessels get tarnished by reacting with air and water, due to which a layer is formed, which mainly contains black copper oxide and green copper hydroxide, which is basic in nature. The citric acid in lemon dissolve this layer and washes off easily.
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