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CBSE TEST PAPER SCIENCE Class-10 Metal and Non-metals Important questions

1: A metal is found in liquid state in nature .It is less reactive than hydrogen .It occurs as sulphide ore .Describe the reactions how can we extract this metal from its ore .Name the ore also.
2: Explain why
(i) Aluminium cannot be extracted by reducing alumina with carbon.
(ii)Concentrated HNO3 can be stored in aluminum containers.
(iii)Aluminium is used for making transmission wires.
(iii) 24 carat gold cannot be used for making ornaments.
3: An alkali metal A gives a compound B (molecular mass=40) on reacting with water .The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B, and C and give the reaction involved.
4: A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen.
5: Given below are the steps for extraction of copper from its ore .Write the reaction involved
(i)Roasting of copper (I) sulphide.
(ii)Reduction of copper (I) oxide with copper (1) sulphide.
(iii) Draw a neat and well labelled diagram for electrolytic refining of copper.
6: An element A burns with golden flame in air .It reacts with another element B, atomic number 17 to give a product C .An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen .Identify A, B, C and D. Also write down the equations for the reactions involved.
7: A metal which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature .Identify the metal and its ore and give the reaction involved.
8: Give reasons
(i)Copper is used to make hot water tanks but steel is not.
(ii) Tarnished copper vessels being cleaned with lemon or tamarind juice.
(iii)Metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters.
(iv) A salt which does not conduct electricity in the solid state becomes a good conductor in molten state
(v) Why ionic compounds have high melting points?
(vi) Why sodium is kept immersed in kerosene oil?
(vii) Why metals like potassium and sodium catch fire when treated with water?
(viii) Why metals are hard and have high melting point?
View Solution
1. The metal is mercury. It occurs as HgS (cinnabar).
2HgS(s) + 3O2(g) + Heat ------->2HgO(s) + 2SO2(g)
2HgO(s) + Heat ---------> 2Hg(l) + O2
2. i) Aluminium is high up in the reactivity series and is very reactive. Thus it cannot
be obtained from it's compounds by heating with carbon. This is because aluminium
has more affinity for oxygen than carbon. Therefore aluminium is obtained by electrolytic reduction.
ii) Concentrated HNO3 can be stored in aluminium containers because concentrated HNO3 does not react with aluminium, so no hydrogen gas is evolved.
iii) Aluminium is used for making transmission wires because it is ductile
iv) Pure gold, known as 24 carat gold, is very soft. It is, therefore, not suitable for making jewellery. It is alloyed with either silver or copper to make it hard. 
3. The alkali metal is sodium, ie A=Na, now they say that a compound B is formed when A reacts with water:
2 Na + 2 H2O ----------> 2 NaOH + H2
So now we have our compound B sodium hydroxide, ie B= NaOH. Next they say that this compound B when treated with aluminium oxide, ie Al2O3, gives a soluble compound C: 
Since NaOH and Al2O3 doesn't give us a soluble compound we add 3 molecules of water, ie H2O)
2 NaOH + Al2O3 + 3 H2O -------> 2 NaAl(OH)4
Sodium aluminate is soluble in water so therefore compound C is sodium aluminate, ie C=NaAl(OH)4
4. Metal M is Copper (Cu) and the black coloured product is copper oxide
2Cu + O2 ------------------->2CuO                                                                                                  
5. i) 2Cu2S + 3O2(g) + Heat -----> 2Cu2O(s) + 2SO2(g)
   ii) 2Cu2) + Cu2S + Heat---------> 6Cu(s) + SO2(g)
6. A=Na, B=Cl, C=NaCl, D=NaOH
Burning of Sodium:
2 Na + O2 ------> Na2O2
Reaction of Sodium with Chlorine:
2Na + Cl2 --------> 2NaCl
Electrolysis of Brine:
NaCl + H2O ---electrolysis-------> NaOH + H2 + Cl2
7. Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat [Thermit reaction]
4 Al + 3 O2 ----------> 2 Al2O3
The metal is aluminium (Al) and it's ore is aluminium oxide (Al2O3)
8.  i) That's because copper is a better conductor of heat than steel, so the water heats up  faster in the copper tank.
ii) Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer.
iii) Metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters because metal halides tend to be soluble in water and so have dissolved out of the rocks and into the lakes/seas over time
(iv) Salt is composed of positive sodium ions and negative chloride ions. In solid these ions are arranged with great force of attraction and unable to move. So in melted state its ions become free to move and conduct electricity.
(v) Ionic solids have crystalline structure in which there is strong inter ionic attraction. So large amount of energy is needed to overcome this force of attraction.
(vi) sodium is kept immersed in kerosene oil because sodium react with air to form Na2O (sodium oxide
(vii) The reaction between sodium and water is so violent that the H2 gas released catches fire .
Reaction:- 2Na(s) + 2H2O(l) ---------> 2NaOH(aq) + H2(s) + heat energy
(viii) Metals are hard and have high melting point because of their crystalline structure metals are hard.

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