CBSE Class 10 Chemistry Metals And Non Metals Worksheet Set 15

This Class 10 Chemistry worksheet, Set 15, gives 21 quick revision questions with answers from Chapter 3, Metals and Non-metals. It has ten true or false statements to correct, nine very short questions on definitions, alloys and reactivity, and two questions on electronic configuration.

True or False

Question 1. True or False: Metals occur in nature only as free elements.
Answer:
False. Unreactive metals such as gold occur free, but most metals occur as compounds (ores) and very reactive metals never occur free.
In simple words: Metals occur both free and as compounds.

Teacher's Note:
1. Correct statement: metals occur in free and combined states.
2. The position in the reactivity series decides the state of occurrence.

Question 2. True or False: Solder is an alloy of lead and tin.
Answer:
True. Solder (lead and tin) has a low melting point and is used to join wires.
In simple words: Solder is a lead and tin alloy.

Teacher's Note:
1. Know the alloys: solder, brass, bronze and stainless steel.
2. Low melting point makes it useful for joining wires.

Question 3. True or False: Metals can form positive ions by losing electrons.
Answer:
True. Metal atoms have few valence electrons and lose them to form cations such as Na⁺, Mg²⁺ and Al³⁺.
In simple words: Metals lose electrons and become positive ions.

Teacher's Note:
1. This is why metals are called electropositive.
2. Non-metals gain electrons to form negative ions.

Question 4. True or False: Different metals have the same reactivities with water and dilute acids.
Answer:
False. Different metals have different reactivities. Sodium reacts violently with cold water, magnesium only with hot water and copper not at all.
In simple words: Every metal reacts differently.

Teacher's Note:
1. This difference is the basis of the reactivity series.
2. Give examples to justify your answer.

Question 5. True or False: Electrovalent compounds will conduct electricity in solid state as ions are present in them.
Answer:
False. In the solid state the ions are held in fixed positions and cannot move. Ionic compounds conduct only in the molten state or in aqueous solution.
In simple words: Ions must be free to move to carry current.

Teacher's Note:
1. Correct statement: ionic compounds do not conduct in the solid state.
2. Free ions are needed for conduction.

Question 6. True or False: Roasting is done for sulphide ores.
Answer:
True. Sulphide ores are heated strongly in excess air to convert them to oxides, for example 2ZnS + 3O₂ → 2ZnO + 2SO₂.
In simple words: Sulphide ores are roasted.

Teacher's Note:
1. Carbonate ores are calcined.
2. Roasting needs a supply of air.

Question 7. True or False: Aluminium oxide can be reduced to aluminium, using carbon (coke) as a reducing agent.
Answer:
False. Aluminium has a greater affinity for oxygen than carbon has, so carbon cannot reduce Al₂O₃. Aluminium is obtained by electrolysis of molten alumina.
In simple words: Carbon is not strong enough to reduce aluminium oxide.

Teacher's Note:
1. Correct statement: Al₂O₃ is reduced by electrolysis.
2. Compare the metal with carbon in the reactivity series.

Question 8. True or False: Reaction that takes place in aluminothermic process is called thermite reaction.
Answer:
True. Reduction of a metal oxide by aluminium (aluminothermy) is called the thermite reaction.
In simple words: Aluminothermy and the thermite reaction are the same.

Teacher's Note:
1. It is used for welding rails.
2. Example: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat.

Question 9. True or False: In electrolytic refining of copper, pure copper is taken as anode.
Answer:
False. Impure copper is made the anode and a thin strip of pure copper is the cathode.
In simple words: Impure metal is the anode.

Teacher's Note:
1. Correct statement: pure copper is the cathode.
2. The electrolyte is acidified copper sulphate.

Question 10. True or False: Rusting of iron does not take place in boiled distilled water.
Answer:
True. Boiled distilled water has no dissolved air (oxygen), and rusting needs both air and water.
In simple words: No air means no rust.

Teacher's Note:
1. A layer of oil on boiled water keeps air out.
2. Rusting needs oxygen and moisture together.

Very Short Answer Questions

Question 11. Name two metals which catch fire if kept in open air.
Answer:
Sodium and potassium catch fire if kept in open air, so they are stored under kerosene.
In simple words: Sodium and potassium burn in air.

Teacher's Note:
1. Store such metals under oil.
2. They react with oxygen of the air.

Question 12. Name the three metals which do not react with water at all.
Answer:
Copper, silver and gold do not react with water, even as steam.
In simple words: Copper, silver and gold do not react with water.

Teacher's Note:
1. They lie below hydrogen in the series.
2. Platinum does not react either.

Question 13. What are metalloids ?
Answer:
Elements that show properties of both metals and non-metals are called metalloids. Examples: boron, silicon, germanium and arsenic.
In simple words: Metalloids are part metal and part non-metal.

Teacher's Note:
1. They lie along the zig-zag line in the periodic table.
2. Silicon is used as a semiconductor.

Question 14. A metal ‘X’ displaces metal ‘Y’ from Y₂(SO₄)₃ aqueous solution. Which metal is more reactive ‘X’ or ‘Y’ ?
Answer:
Metal X is more reactive. A more reactive metal displaces a less reactive metal from the solution of its salt, so X can take the place of Y in Y₂(SO₄)₃ and Y is set free as the metal.
In simple words: The metal that displaces the other is the more reactive one.

Teacher's Note:
1. Displacement always goes from the more reactive to the less reactive metal.
2. Write X + Y₂(SO₄)₃ → X salt + Y.

Question 15. Define gangue.
Answer:
The earthy impurities such as sand, soil and rocky material present in an ore are called gangue (matrix).
In simple words: Gangue is the waste material mixed with the ore.

Teacher's Note:
1. Ore concentration removes the gangue.
2. Do not confuse gangue with mineral.

Question 16. What is an amalgam ?
Answer:
An amalgam is an alloy in which one of the metals is mercury.
In simple words: An amalgam is an alloy that contains mercury.

Teacher's Note:
1. Brass and bronze are not amalgams.
2. Mercury is the only liquid metal.

Question 17. Which one of the metal in the following metals is (a) most reactive (b) least reactive Au, Na, Cu, Ca
Answer:
(a) Sodium (Na) is the most reactive of the four. (b) Gold (Au) is the least reactive.
In the reactivity series the order is Na > Ca > Cu > Au.
In simple words: Sodium is at the top and gold is at the bottom of this group.

Teacher's Note:
1. Arrange the four metals using the series before answering.
2. Gold does not react with air, water or acids.

Question 18. Which two major constituents form the alloy duralumin?
Answer:
Duralumin is an alloy of aluminium and copper (with small amounts of magnesium and manganese). It is light and strong, so it is used in aircraft parts.
In simple words: Duralumin is mainly aluminium with some copper.

Teacher's Note:
1. Alloys are made to improve strength and hardness.
2. Learn the composition of common alloys.

Question 19. Name the constituents of an alloy called German silver.
Answer:
German silver is an alloy of copper, zinc and nickel. It does not contain any silver.
In simple words: German silver has no silver in it.

Teacher's Note:
1. Brass is copper and zinc; German silver adds nickel.
2. The name comes from its silvery look.

Electronic Configuration

Question 20. Write electronic configuration of an element having atomic number 11.
Answer:
Sodium has 11 electrons. They are arranged as K = 2, L = 8, M = 1, so the electronic configuration is 2, 8, 1. It has one valence electron, so it is a metal that forms Na⁺ (2, 8).
In simple words: Fill the shells 2, 8, 8 in order: eleven electrons give 2, 8, 1.

Teacher's Note:
1. Fill K, L and M shells in order.
2. One valence electron means a metal with valency 1.

Question 21. Write electronic configuration of an element having atomic number 13.
Answer:
Aluminium has 13 electrons: K = 2, L = 8, M = 3, so the configuration is 2, 8, 3. It has three valence electrons, so it is a metal that forms Al³⁺ (2, 8).
In simple words: Thirteen electrons fill the shells as 2, 8, 3.

Teacher's Note:
1. Three valence electrons give valency 3.
2. Metals lose valence electrons to become stable.