NCERT Chapter 3 Science Class 10 Solution || METALS AND NON METALS || Chemistry || Science ||

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 Ques 1: Which of the following pairs will give displacement reactions?  

(a) sodium chloride solution and copper metal

(b) magnesium chloride solution and aluminium metal

(c) ferrous sulphate solution and silver metal

(d) silver nitrate solution and copper metal.

Ans 1: (d) silver nitrate solution and copper metal  

Ques 2: Which of the following methods is suitable for preventing an iron frying pan from  rusting?

(a) Applying grease

(b) Applying paint

(c) Applying a coating of zinc

(d) All of the above.

Ans 2: (c) Applying a coating of zinc

(We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed. The process of layering of zinc surface on the utensils or on the metals are known as galvanisation.)

Ques 3: 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

(a) calcium

(b) carbon

(c) silicon

(d) iron

Ans 3: (a) The element is likely to be calcium. As given in activity 1.4 .

Ques 4: Food cans are coated with tin and not with zinc because  

(a) zinc is costlier than tin.

(b) zinc has a higher melting point than tin.

(c) zinc is more reactive than tin.

(d) zinc is less reactive than tin.

Ans 4: (c) Food cans are coated with tin and not with zinc because zinc is more reactive than tin. Zinc reacts vigorously with oxygen as compare to tin.

Ques 5: You are given a hammer, a battery, a bulb, wires and a switch.  

(a) How could you use them to distinguish between samples of metals and non- metals?  

(b) Assess the usefulness of these tests in distinguishing between metals and non – metals.  

Ans 5: (a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. As we know, metals conduct electricity. Similarly,  we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.  

(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved  in these tests.  

Ques 6: What are amphoteric oxides? Give two examples of amphoteric oxides.  

Ans 6: Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.  

Examples: aluminium oxide (Al 2 O 3)

Al 2 O 3 + 6HCl → 2AlCl3 + 3H2O [ Basic ]

Al 2 O 3 + 2NaOH → 2NaAlO2 + H2O [ Acidic ]

Zinc oxide (Z n O) , Magnesium oxide (Mg O), Calcium oxide(C a O) is also an amphoteric oxide.

Ques 7: Name two metals which will displace hydrogen from dilute acids, and two metals  which will not.  

Ans 7: Metals that are more reactive than hydrogen so, they displace it from dilute acids.  

For example: sodium, magnesium and potassium. Metals that are less reactive than hydrogen do not displace it.  

For example: copper , mercury and silver.

Ques 8: In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?  

Ans 8: In the electrolytic refining of a metal M:  

 Anode → Impure metal M

Cathode → Thin strip of pure metal M

Electrolyte → Solution of salt of the metal M

Ques 9: Prat y us h took sulphur powder on a spatula and heated it. He collected the gas  evolved by inverting a test tube over it, as shown in figure below.

 (a) What will be the action of gas on                      (i) dry litmus paper?                                                   (i i) moist litmus paper?  

(b) Write a balanced chemical equation for the reaction taking place.

Ans 9: (a) (i) There will be no action on dry litmus paper. Because there is no any free ions of hydrogen atom. 

(i i) Since the gas is sulphur dioxide (SO 2), it turns moist blue litmus paper to red because sulphur dioxide reacts with moisture to form sulphurous acid.

(b) 

Ques 10: State two ways to prevent the rusting of iron.  

Ans 10: Two ways to prevent the rusting of iron are:

Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. It is the cheaper of protection from corrosion. A very large amount of money is wasted in preservation from corrosion. Hence, rusting is prevented.  

Galvanisation: In this method, an iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.  

Ques 11: What type of oxides is formed when non-metals combine with oxygen?  

Ans 11: Non-metals combine with oxygen to form acidic oxides.  

For example: S + O2 → SO 2

Ques 12: Give reasons: 

(a) Platinum, gold and silver are used to make jewellery.

(b)Sodium, potassium and lithium are stored under oil.

(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.  

(d)Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Ans 12: (a) Platinum, gold, and silver are used to make jewellery because they are very  lustrous. Also, they are very less reactive and do not corrode easily in the direct case of contact with oxygen and moisture also.  

(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.  

(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.  

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.

Ques 13: 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.  

Ans 13: 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(C a CO 3). The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels  are cleaned with lemon or tamarind juice to give the surface of the copper vessel  its characteristic lustre.  

Ques 14: Differentiate between metal and non-metal on the basis of their chemical properties.

Ans 14: The basic difference between the metals and non-metals are given in the below figure: 


Ques 15: A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold  bangles to him which he dipped in a particular solution. The bangles sparkled like  new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?  

Ans 15: He must have dipped the gold metal in the solution of aqua regia − a 3:1 mixture  
of concentrated HCl and concentrated Nitric acid (H N O 3) . Aqua regia is a fuming, highly corrosive liquid. It  dissolves gold in it. After dipping the gold ornaments in aqua regia, the outer layer of gold gets dissolved and the inner shiny layer appears. That is why the weight  
of gold ornament reduced. After that he can get that gold. 

Ques 16: Give reasons why copper is used to make hot water tanks and not steel (an alloy  
of iron). 
Ans 16: Copper(Cu) does not react with cold water, hot water, or steam. However, iron reacts  with steam. If the hot water tanks are made of steel (an alloy of iron), then iron  would react vigorously with the steam formed from hot water.
            
              Fe + H 2 O → Fe 3 O 4 + H 2↑

That is why copper is used to make hot water tanks, and not steel.

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