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प्रश्न
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
उत्तर
Copper reacts with moist carbon dioxide in the air to form copper carbonate, which causes a copper vessel to lose its shiny brown surface and form a green layer of copper carbonate. The citric acid present in lemon or tamarind neutralises the base copper carbonate and dissolves the layer. That is why tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface its characteristic lustre.
\[\ce{2Cu + \underset{(Present in air)}{H2O + CO2 + O2} -> \underset{(green)}{\underset{Basic copper carbonate}{CuCO3.CU(OH)2}}}\]
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संबंधित प्रश्न
Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.
| Metal | Iron (II) sulphate | Cooper (II) sulphate | Zinc sulphate | Silver nitrate |
| A | No reaction | Displacement | ||
| B | Displacement | No reaction | ||
| C | No reaction | No reaction | No reaction | Displacement |
| D | No reaction | No reaction | No reaction | No reaction |
Use the Table above to answer the following questions about metals A, B, C and D.
- Which is the most reactive metal?
- What would you observe if B is added to a solution of copper (II) sulphate?
- Arrange the metals A, B, C and D in the order of decreasing reactivity.
Explain the following reaction with the help of a balanced chemical equation:
Magnesium reacts with hot water.
How would you show that silver is chemically less reactive than copper?
Complete and balance the following equation:
Na2O + H2O →
Complete and balance the following equation:
Fill in the following blank with suitable word:
Ordinary aluminium strips are not attacked by water because of the presence of a layer of ................. on the surface of aluminium.
Which of the following elements would yield a neutral oxide?
Na, S, C, K, H
How do non-metals react with hydrogen? Explain with an example.
Can we keep sodium immersed under water? Why?
Write the chemical equation of the reaction which takes place when iron reacts with dilute sulphuric acid. What happens when the gas produced is ignited with a burning matchstick?
Name one metal which displaces copper from copper sulphate solution and one which does not.
The least reactive metal among the following is:
(a) sodium
(b) silver
(c) copper
(d) lead
A metal less reactive and another metal more reactive than hydrogen are:
(a) aluminium and lead
(b) iron and magnesium
(c) copper and tin
(d) copper and mercury
An element E forms an oxide E2O. An aqueous solution of E2O turns red litmus paper blue.
(a) What is the nature of the oxide E2O?
(b) State whether element E is a metal or a non-metal.
(c) Give one example of an element like E.
Metal A burns in air, on heating, to form an oxide A2O3 whereas another metal B burns in air only on strong heating to form an oxide BO. The two oxides A2O3 and BO can react with hydrochloric acid as well as sodium hydroxide solution to form the corresponding salts and water.
(a) What is the nature of oxide A2O3?
(b) What is the nature of oxide BO?
(c) Name one metal like A.
(b) Name one metal like B.
When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding sodium metal to water catches fire. Why is it so?
Explain the following:
Reactivity of aluminium decrease if it is dipped in nitric acid.
A cable manufacturing unit tested few elements on the basisof their physical properties.
| Properties | W | X | Y | Z |
| Malleable | Yes | No | No | Yes |
| Ductile | Yes | No | No | Yes |
| Electrical conductivity | Yes | Yes | Yes | No |
| Melting Point | High | Low | Low | High |
Which of the above elements were dicarded for usage by the company?
Metals are generally solid. Which of the following metals is in the liquid state at room temperature?
Find the odd one out:
