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प्रश्न
Explain why, the surface of some metals acquires a dull appearance when exposed to air for a long time.
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उत्तर १
Some metals, when exposed to air for a long time, react with oxygen in the atmosphere to form a dull layer of metal oxide on their surfaces. This makes the metals look dull.
उत्तर २
Most of the metals are reactive towards air. They react with oxygen present in the air to form metal oxides. The metal oxide formation appears on the surface of the metals as a thin layer. This thin layer formation of metal oxide on the metallic surface causes the dull appearance of the metals. Thus, the surface of some metals acquires a dull appearance when exposed to air for a long time.
संबंधित प्रश्न
A solution of CuSO4 in water is .................... in colour.
(a) Pink
(b) Blue
(c) Colourless
(d) Green
_________ solution is blue in colour.
(a) CuSO4
(b) FeSO4
(c) ZnSO4
(d) Al2(SO4)3
Iron is
(a) More reactive than zinc
(b) More reactive than aluminium
(c) Less reactive than copper
(d) Less reactive than aluminium
Write the chemical reaction when iron reacts with dilute H2SO4.
Write the electron-dot structures for sodium, oxygen and magnesium.
An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be:
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.
Complete and balance the following equation:
Na + O2 →
Complete and balance the following equation:
Na2O + H2O →
Complete and balance the following equation:
Cu (NO3)2 (aq) + Zn(s) →
What happens when calcium reacts with chlorine? Write an equation for the reaction which takes place
Name two metals which cannot displace hydrogen from dilute acids.
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?
An element X forms two oxides XO and XO2. The oxide XO is neutral but XO2 is acidic in nature. The element X is most likely to be:
(a) sulphur
(b) carbon
(c) calcium
(d) hydrogen
An element is soft and can be cut with a knife. If is very reactive and cannot be kept open in the air. It reacts vigorously with water. The element is most likely to be:
(a) Mg
(b) S
(c) P
(d) Na
If A, B, C, D, E, F, G, H, I, J and K represent metals in the decreasing order of their reactivity, which one of them is most likely to occur in a free state in nature?
Write the chemical equation of the above process.
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?
