Silver articles become black when kept in open for some time, whereas copper vessels lose their shiny brown surfaces and gain a green coat when kept in open. Name the substances present in air with which these metals react and write the name of the products formed.

Silver articles become black when kept in open for some time, whereas copper vessel lose their shiny brown surfaces and gain a green coat when kept in open because these metals undergoes corrosion. Silver articles reacts with sulphur compounds such as hydrogen sulphide present in the air to form silver sulphide ( Ag 2 S ), which is the black substance formed. This process is called tarnishing of silver whereas copper reacts slowly with CO 2 and water present in the air to form green coating of mixture of copper carbonate and copper hydroxide.

Give reason: Metals like sodium and potassium are stored under oil.

Metals like sodium and potassium are stored under oil because they are highly reactive metals, they vigorously react with oxygen and moisture and may catch fire. The oil prevents the reaction of alkali metals.

Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.

Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals because these metals are highly reactive and have greater affinity for oxygen than carbon. Oxides of less reactive metals like zinc, iron and copper etc. can be reduced to their respective metals by carbon. Sodium, magnesium and aluminium are placed at the top of the reactivity series. Reactivity of the metals or the elements increases as we move bottom to top in the reactivity series. These highly reactive metals are obtained by the electrolytic reduction of their molten ores. For example, sodium is extracted from brine or either molten NaCl by the process of electrolysis. Process of electrolysis: Molten sodium chloride is taken in a cell and two electrodes are placed in it. On passing the electricity to the cell, the ions present in the molten salt moves towards their respective electrodes. Sodium ion moves towards the cathode and gets reduced to sodium metal. Chloride ion moves towards the anode and gets oxidised into chlorine gas. 2 NaCl molten salt ⇄ 2 Na + + 2 Cl - At cathode: 2 Na + + 2 e - → 2 Na sodium metal At anode: 2 Cl - → Cl 2 chlorine gas + 2 e -

A student added few pieces of aluminium metal to two test tubes A and B containing aqueous solutions of iron sulphate and copper sulphate. In the second part of her experiment, she added iron metal to another test tubes C and D containing aqueous solutions of aluminium sulphate and copper sulphate. In which test tube or test tubes will she observe colour change ? On the basis of this experiment, state which one is the most reactive metal and why.

Reactions taking place in different test tubes can be given as, Test tube A: 3 FeSO 4 + 2 Al → ( Al 2 SO 4 ) 3 + 3 Fe Test tube B: 3 CuSO 4 + 2 Al → ( Al 2 SO 4 ) 3 + 3 Cu Test tube C: ( Al 2 SO 4 ) 3 + 3 Fe → No reaction Test tube D: CuSO 4 + Fe → FeSO 4 + Cu She will observe colour change only in test tubes A, B and D. In test tube A colour change from green to colourless is observed because aluminium is more reactive than iron, it will displace iron. She will observe colour change from blue to colourless in test tube B as aluminium is more reactive than copper. She will also observe colour change in test tube D from blue to light green as iron is more reactive than copper. These are examples of displacement reactions. Aluminium is the most reactive metal among the given metals because it is placed at the top of the reactivity series.

How is copper extracted from its sulphide ore? Explain the various steps supported by chemical equations. Draw labelled diagram for the electrolytic refining of copper.

Sulphide ores are usually converted into oxides by roasting. 2 Cu 2 S + 3 O 2 → Cu 2 O + 2 SO 2 2 Cu 2 O + Cu 2 S → Heat 6 Cu + 2 SO 2 The impure metal is made as the anode while strip of pure metal acts as cathode. A solution of salt of metal acts as electrolyte. On passing electric current through the solution, pure metal gets deposited at the cathode. The more reactive impurities present in the metal to be purified go into solution and there, The less reactive impurities fall to the bottom of the electrolytic cell.

Write the steps involved in the extraction of pure metals in the middle of the activity series from their carbonate ores.

Carbonate ores are calcined to expel carbon dioxide. Carbonate ores are then converted into oxides. Zinc is a metal in the middle of the activity series. First zinc carbonate is converted into zinc oxide. ZnCO 3 → ZnO + CO 2 Metals in the middle of the activity series cannot be obtained by heating their compounds alone, They require to be heated with a reducing agent, usually carbon (coke). This process is known as smelting. Zinc oxide is then heated with coke to obtain pure zinc. ZnO + C → Zn + CO

What are amphoteric oxides? Give an example. Write balanced chemical equations to justify your answer.

Those oxides which behave as both acidic and basic oxides are called amphoteric oxides. They have properties of acidic as well as basic oxides that neutralize both acids and bases. Amphoteric oxides of metals dissolve in both acidic and alkaline solutions. Examples of amphoteric oxides are as follows: ZnO s + 2 HCl aq → ZnCl 2 aq + H 2 O l ZnO s + 2 NaOH aq → Na 2 ZnO 2 aq + H 2 O l

Give reasons- Platinum, gold and silver are used to make jewellery.

Platinum, gold and silver are used to make jewellery because they are highly malleable and ductile as well as lustrous. Also, they are less reactive and do not corrode easily.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 3 - Metals and Non-metals>CBSE-2023 (Outside Delhi - I)>Q 15

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10th CBSE

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Metal oxides generally react with acids, but few oxides of metal also react with bases. Such metallic oxides are:

$I . MgO II . ZnO III . {Al}_{2} O_{3} IV . CaO$

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Important Questions on Metals and Non-metals

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10th CBSE

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 3 - Metals and Non-metals>CBSE-2023 (Outside Delhi - I)>Q 16

Select the appropriate state symbols the products given as X and Y in the following chemical equation by choosing the correct option from table given below:

${Zn}_{(s)} + H_{2} {SO}_{4 (l)} \to {ZnSO}_{4 (X)} + H_{2 (Y)}$