Thursday, August 23, 2012

Chemistry X –Ch:Metal and Non Metal SA-I Guess Question

Chemistry X –Chapter :Metal and Non Metal SA-I Guess Question
What are amphoteric oxides? Why is it that non metals do not displace hydrogen from dilute acid?
The oxides which are acidic as well as basic in nature are called amphoteric oxides. ZnO and Al2Oare amphoteric oxides.
           Al2O3 + 6HCl ® 2AlCl3 + 3H2O
           Al2O3 + 2NaOH ®2NaAlO2 + H2O
Non metals cannot lose electrons so that H+ ions become hydrogen gas.
What is anodizing? What is its use?
The process of forming thick oxide layer of aluminium oxide that makes it resistant to further corrosion.
What is Aqua regia? What is its use?
It is a mixture of concentrated HCl and concentrated HNO3 in the ratio 3:1. It can dissolve gold and platinum. It dissolve gold and silver and reduce weight
Give reason: Aluminium is highly reactive metal, but it is used to make utensils for cooking.
Aluminium form thick layer of aluminium oxide at ordinary temperature. This layer prevents further oxidation that slow down rusting.
Explain why (a) Iron articles are frequently painted.
(b)  Iron sheets are coated with Zinc layer.
(a) Iron articles are frequently painted to prevent further rusting.
(b) Iron sheets are coated with Zinc layer so that  it is not exposed to air and water ad Zn does not rust and rusting is prevented.
On adding dilute HCl acid to copper oxide powder, the solution formed is blue – green. Predict the new compound formed which imparts a blue – green colour to the solution? Write its equation.
CuO +  HCl ® CuCl2 + H2O
Here Copper (II) Chloride imparts a blue – green colour to the solution
Name the property of metal used in the following cases- (i) Aluminium foil (ii) Metal jewellery (iii)  Cable wires (iv) Bells
(i) Aluminium foil - Malleability
 (ii) Metal jewellery – Malleability , Ductility, lustrous
(iii)  Cable wires-Ductility
 (iv) Bells-Sonorous
How can you prove that Zinc is more reactive than Copper?
When we add Zn in CuSO4 solution ,Blue solution became colourless and a redish brown Cu gets deposited hence ZN > Cu
Zn +  CuSO4 ®ZnSO4 + Cu
 Explain the electrolytic refining of impure Copper.
The impure copper metal is purified by the process of electrolytic refining to get pure   copper metal.
The impure metal is made the anode and a strip of pure copper cathode. These are immersed in a copper sulphide solution with a little sulphuric acid added to it. On passing an electric current the anode begins to dissolve pure copper gets deposited on the cathode. The impurity either dissolves in the solution or deposited below the anode as anode mud.
At anode : Cu (Copper)
®Cu2+ (copper ion)
At cathode : Cu2+ (Copper ion)
® Cu (Copper atom) deposits on cathode
Thus pure copper is obtained at the cathode.
What is Thermite reaction?  Give its one use.
The reaction of Al2O3 with Al is highly exothermic that melt iron. This reaction is called Thermite reaction. It is used for welding broken part of iron machinery
Fe2O3 + 2Al  ----Ignite----®Fe (l)  + Al2O3
What is amalgam?
amalgam is an alloy of mercury with various metals used for dental fillings caused by tooth decay
Q. 12
Magnesium when reacts with hot water, starts floating.  Why?
Magnesium when reacts with hot water starts floating bubbles of H2 gas get stick to the surface.  Mg + H2O ® Mg(OH)2    + H2

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