CBSE Class 10 Science Metals and Non metals Worksheet A

Question. How are covalent bonds formed ?
Answer : Covalent bonds are formed by the sharing of electrons between atoms. By sharing their outermost valence electrons, atoms can fill up their outer electron shell and gain stability.

Question. 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.
Answer : 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 silver articles reacts with sulphide compounds such as hydrogen sulphide present in the air to form silver sulphide (Ag₂S) whereas copper reacts slowly with CO₂ and water present in the air to form green coating of mixture of copper carbonate and copper hydroxide.

Question. Name one metal which has a low melting point.
Answer : Cesium.

Question. What name is given to those metal oxides which show basic as well as acidic behaviour ?
Answer : Amphoteric oxides.

Question. Name two metals which form amphoteric oxides.
Answer : Aluminium and zinc.

Question. Give an example of a metal which : 
(a) is a liquid at room temperature.
(b) can be easily cut with a knife.
(c) is the best conductor of heat.
(d) is a poor conductor of heat.
Answer : (a) Metal that exists in liquid state at room temperature → Mercury
(b) Metal that can be easily cut with a knife → Sodium, Potassium
(c) Metal that is the best conductor of heat → Silver, Gold
(d) Metals that are poor conductors of heat → Mercury and lead

Very Short Answer Questions

Question. Why do the non-metals not displace hydrogen from dilute acids? 
Answer : Non-metals being acceptor of electrons, cannot give electrons to the hydrogen ions of acid to reduce them
to hydrogen gas. Hence non-metals do not displace hydrogen from dilute acids.

Question. Name two metals which displace hydrogen from dilute acids and two metals which will not.
Answer : Zinc (Zn) and magnesium (Mg) metals can displace hydrogen from dilute acids. Copper (Cu) and silver (Ag) can not displace hydrogen from dilute acids.

Question. In the electrolytic refining of a metal M, what would you take as the anode, cathode and electrolyte?
Answer : We should take impure metal M as anode, a thin strip of pure metal M as cathode and a salt solution of metal M as an electrolyte.

Question. Name a metal for each case:
(i) it does not react with cold as well as hot water but reacts with any other physical state of water.
(ii) it does not react with any physical state of water. 
Answer : (i) Aluminium (Al)

Question. State two ways for preventing rusting of iron articles. 
Answer : (i) By applying grease and paints on the iron articles.
(ii) By coating of zinc layer over the iron articles by Galvanisation process.

Question. 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?
Answer : Copper oxide reacts with acid but copper itself does not react. So, the tarnished copper vessels can be washed by acidic substances. It removes the corroded part (copper oxide) and pure copper is left behind.

Question. Name the following: 
(a) A metal which is preserved in kerosene (b) A lustrous coloured non metal
(c) A metal which can melt while kept on palm. (d) A metal, which is a poor conductor of heat.
(e) A metal which can be easily cut with a knife. (f) A metal which is a liquid at room temperature.
Answer : (a) Sodium (b) Iodine (c) Gallium and Caesium
(d) Lead and mercury (e) Sodium (f) Mercury

Question. Give reason why copper is used to make hot water tanks but steel (an alloy of iron) is not?
Answer : Copper is a better conductor of heat as compared to steel, therefore hot water tanks are made of copper.

Question. Explain the meanings of malleable and ductile.
Answer : Malleable : Substances that can be converted into thin sheets by beating are called malleable. Most of the metals are malleable. Gold and silver are most malleable metals.
Ductile : Substances that can be drawn into thin wires are called ductile. Most of the metals are ductile. Gold is the most ductile metal.

Question. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer : Copper 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.
3Fe + 4H₂O    →    Fe₃O₄    +   4H₂
Iron Steam          Iron oxide   Hydrogen
That is why copper is used to make hot water tanks and not steel.

Question. In the formation of a compound XY₂ atom X gives one electron to each Y atom. What is the nature of bond in XY₂ ? Give two properties of XY₂.
Answer : XY₂ has ionic bonds. XY₂ would conduct electricity when dissolved in water and XY₂ would have high melting and boiling point.

Question. An element ‘A’ has two electrons in the outermost shell of its atom and combines with an element ‘B’ having seven electrons in the outermost shell, forming the compound AB₂. The compound when dissolved in water conducts electric current. Giving reasons, state the nature of chemical bond in the compound.
Answer : AB₂ forms ionic bonds because an aqueous solution of an ionic compound conducts electricity because there are plenty of free ions in the solution which are able to conduct electric current.

Question. What happens when a copper rod is placed in silver nitrate solution ?
Answer : Copper displaces silver as it is more reactive. A blue coloured solution will be formed and grey coloured solution will be deposited at the bottom of container.

Question. Aluminium strips were placed in a solution of copper sulphate. After one hour, it was observed that the colour of solution changes. What will be the colour of the solution ? Give reasons.
Answer : Aluminium will displace Cu from copper sulphate solution. As a result, the solution will be colourless.

Question. A piece of granulated Zn was dropped into copper sulphate solution. Write down the colour change that you will observe.
Answer : When a piece of granulated Zn was dropped into copper sulphate solution, blue colour solution become colourless, reddish brown Cu gets deposited.

Short Answer Questions

Question. A thin zinc plate was kept in a glass container having CuSO4 solution. On examining it was found that the blue colour of the solution is getting lighter and lighter. After a few days when the zinc plate was taken out of the solution, a number of small holes were noticed in it. State the reason and write chemical equation of the reaction. 
Answer : A strip of zinc metal is put in copper sulphate solution. The blue colour of copper sulphate solution fades gradually due to the formation of colourless zinc sulphate solution. Since zinc is more reactive than copper, zinc displaces copper from copper sulphate solution. Zinc metal is consumed and hence a number of small holes were formed in the zinc strip.
CuSO4 (aq) + Zn (s) ⎯⎯⎯→ ZnSO4 (aq) + Cu (s)
Copper Sulphate Zinc Zinc Sulphate Copper
(Blue solution) (Colourless solution)

Question. Reverse of the following chemical reaction is not possible:
Zn (s) + CuSO₄ (aq) ⎯⎯⎯→ ZnSO4 (aq) + Cu (s) Justify this statement with reason. 
Answer : ZnSO₄ (aq) + Cu (s) ⎯⎯⎯→ × (no reaction) Because Cu is less reactive than Zn in the activity series. Therefore, less reactive metal (Cu) does not displace more reactive metal (Zn) from its salt solution. Thus, this reaction is not possible.

Question. A reddish brown coloured metal, used in electrical wires, when powdered and heated strongly in an open china dish, its colour turns black. When hydrogen gas is passed over this back substance, it regains its original colour. Based on the above information answer the following questions:
(i) Name the metal and the black coloured substance formed.
(ii) Write balanced chemical equations for both the reactions.
Answer : (i) The reddish brown coloured metal used in electric wires is Copper.
When copper is heated strongly in air, it combines with oxygen to form Copper (II) oxide, a black oxide.
(ii) 2Cu + O2 Δ⎯⎯⎯→ 2 CuO
Copper Copper (II) Oxide
(black)
CuO + H₂ ⎯⎯⎯→ H₂O + Cu
Copper (Reddish brown)

Question. Write balanced equations for the reaction of:
(i) Aluminium when heated in air. Write the name of the product.
(ii) Iron with steam. Name the product obtained.
(iii) Calcium with water. Why does calcium start floating in water? 
Answer : (i) When aluminium is heated in air, it forms aluminium oxide.
4Al + 3O₂ Δ⎯⎯⎯→ 2Al₂O₃
Aluminium oxide
(ii) When iron is reacted with steam, it forms iron oxide and hydrogen.
3Fe (s) + 4H₂O (g) ⎯⎯⎯→ Fe₃O₄ (s) + 4H₂ (g)
(Steam) Iron oxide
(iii) The reaction of calcium with water is less violent, and the heat evolved in this reaction is not sufficient for hydrogen to catch fire. So calcium starts floating in water because the bubbles of hydrogen gas formed stick to the surface of the metal.
Ca (s) + 2H₂O (l) ⎯⎯⎯→ Ca(OH)₂ (aq) + H₂ (g) + Heat

Question. Define the term ‘metallurgy’, and fill appropriate terms in the blanks: 
The four major steps involved in metallurgy are:
(i) ............. of ore. (ii) Conversion of ore into its ............. .
(iii) Reduction of oxides of ores into ............. . (iv) ............. of metal.
Answer : The various processes involved in the extraction of metals from their ores and their refining are known as metallurgy.
The four major steps involved in metallurgy are:
(i) Concentration of ore. (ii) Conversion of ore into its metal oxide.
(iii) Reduction of oxides of ores into metal. (iv) Refining of impure metal.

Question. State reason for the following:
(i) Lemon is used for restoring the shine of tarnished copper vessels.
(ii) A metal sulphide is converted into its oxide to extract the metal from the sulphide ore.
(iii) Copper wires are used in electrical connections.
Answer : (i) When a copper object remains in damp air for a considerable time, then copper reacts slowly with carbon dioxide and water in air to form a green coating of basic copper carbonate on its surface. If corroded copper vessels are treated with lemon which is acidic in nature, the acid solution dissolves green coloured basic copper carbonate and makes them look shiny.
(ii) It is easier to obtain metals from their oxides (by reduction) than from sulphides. So before reduction, the metal sulphide ore is converted into metal oxide.
(iii) Copper metal is the next best conductor of electricity after silver metal. So electric wires are made of copper (as silver being a costly metal can not be used for making electric wires).

Question. 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? (Imp.)
Answer : The dishonest goldsmith dipped the gold bangles in aqua-regia (which contains 1 part of concentrated nitric acid and 3 parts of concentrated hydrochloric acid by volume). Aqua-regia dissolved a considerable amount of gold from gold bangles and hence reduced their weight drastically. The dishonest goldsmith can recover the dissolved gold from aqua-regia by a suitable treatment.

Question. List four important properties of aluminium which are responsible for its great demand in industry.
Answer : Important properties of aluminium:
(i) It is a light metal.
(ii) It does not corrode as it forms a protective layer of oxide which prevents it from further oxidation.
(iii) It is a good conductor of heat and electricity.
(iv) It is used as a reducing agent in the extraction of metals from the oxide.

Question. You are given samples of three metals—sodium, magnesium and copper. Suggest any two activities to arrange them in order of their decreasing reactivity. 
Answer : Given three metals—sodium (Na), magnesium (Mg), copper (Cu) Activity I. When the three given metals Na, Mg and Cu are added to magnesium chloride solution separately taken in three different test tubes, we will find that displacement reactions will take place in the following manner:
MgCl₂ solution Metals
Displacement reaction Na
No reaction Mg
No reaction Cu
This shows that Na is the most reactive metal as it displaces Mg from MgCl2 solution.
Activity II. When Na, Mg and Cu metals are taken in three different test tubes and CuSO4 solution is added in each test tube, we will find that displacement reactions will take place in the following manner:
CuSO₄ solution Metals
Displacement reaction Na
Displacement reaction Mg
No reaction Cu
This shows that Cu is the least reactive metal.
Order of decreasing reactivity: Na > Mg > Cu.

Question. What are amphoteric oxides ? Give an example. Write balanced chemical equations to justify your answer.
Answer : Those oxides which behave as both acidic and basic oxides are called amphoteric oxides.
Example : Al₂O₃ (Alumina)
(a) Al₂O₃ + 6HCl    →   2AlCl₃ + 3H₂O
Alumina    Acid              Salt
(b) Al₂O₃ + 2NaOH   →   2NaAlO₂ + H₂O
Alumina       Base            Salt

Question. Give reason :
(a) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
(b) Aluminium is a highly reactive metal; still it is widely used in making cooking utensils.
Answer :
(a) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because obtaining a metal from its metal oxide is much easier than from metal carbonates and sulphides.
(b) Aluminium is highly reactive metal still it is widely used in making cooking utensils because it reacts with O₂ present in air to form aluminium oxide that forms a protective layer and protects the metal from corrosion.

Question. Name a metal of medium reactivity and write three main steps in the extraction of this metal from its sulphide ore. 
Answer : Zinc
The steps inolved in extraction of zinc from zinc sulphide are :
(a) Roasting of sulphide ore in the presence of air to convert it into metal oxide.
2ZnS(s)     +    3O₂(g)   Roasting→    2 ZnO(s)   + 2 SO₂(g)
Zinc sulphide     Oxygen                    Zinc oxide      Sulphur dioxide

(b) Reduction of metal oxide with carbon to get the free metal.
ZnO(s) + C(s) → Zn(s) + CO(g)
Zinc oxide Carbon Zinc Carbon-monoxide

(c) Refining of impure metal to get pure metal.

Question. Given below are the steps for the extraction of copper from its ore. Write the chemical equation of the reactions involved in each case.
(a) Roasting of copper(I) sulphide.
(b) Reduction of copper(I) oxide from copper(I) sulphide
(c) Electrolytic refining. 
Answer :
(a) 2Cu₂S(s)    +    3O₂(g)    Roasting→    2Cu₂O(s)    + 2SO₂(g)
Copper(I)              Oxygen                        Copper (I)      Sulphur
sulphide              (From air)                        oxide           dioxide
(Copper glance ore)

(b) 2Cu₂O (s)  +  Cu₂S (s)    Heat →    6Cu(s)  +  SO₂ (g)
Copper(I)            Copper(I)                  Copper     Sulphur
oxide                   sulphide                    metal       dioxide

(c) At cathode :
Cu²⁺      +       2e^–    →      Cu
Copper ion       Electrons     Copper
(From (From     (Deposits    on cathode)
electrolyte)        cathode) 
At anode :
Cu     –    2e–      →            Cu²⁺
Copper atom    Electrons    Copper ion (Goes into 
(From impure  (Given to      electrolyte)
anode)              anode)