CBSE Class 10 Science Metals and Non Metals Assignment Set 06

This CBSE Class 10 Science assignment for Chapter 3, Metals and Non-metals, has 19 questions of 2 and 3 marks with step-by-step answers. It practises the properties of metals, the reaction of metals with water and acids, the reactivity series and the extraction of less reactive metals.

Short Answer Questions (2 Marks)

Question 1. What properties do you think of while categorising elements as metals and non-metals? (2 marks)
Answer:
1. Physical properties: lustre, hardness, malleability, ductility, sonority, and conduction of heat and electricity.
2. Chemical properties: the nature of the oxide formed (basic for metals, acidic or neutral for non-metals) and the reaction with water, acids and other salts.
In simple words: We check physical properties and the way the element reacts.

Teacher's Note:
1. Always give both physical and chemical properties.
2. No single property is enough because of exceptions.

Question 2. Why are metals said to be electropositive? (2 marks)
Answer:
Metals ionise by losing electrons and form positive ions (cations), so they are called electropositive. For example, Na → Na⁺ + e⁻ and Ca → Ca²⁺ + 2e⁻.
In simple words: Metals lose electrons to become positive ions.

Teacher's Note:
1. Non-metals are electronegative.
2. Positive ions are called cations.

Question 3. Some metals do not get oxidised easily at ordinary temperature. Why? (2 marks)
Answer:
The surface of metals like magnesium, aluminium, zinc and lead is covered with a thin, protective layer of oxide. This layer prevents the metal beneath from further oxidation.
In simple words: An oxide film protects the metal.

Teacher's Note:
1. Aluminium oxide is the best example.
2. Iron has no such protective layer, so it rusts.

Question 4. Why do metals generally not form compounds with hydrogen? (2 marks)
Answer:
Metals form compounds by losing electrons, which must be accepted by the other element. Hydrogen does not accept electrons; it forms compounds by losing or sharing electrons. So metals generally do not combine with hydrogen. Only very reactive metals such as Na, K and Ca form hydrides.
In simple words: Metals give electrons and hydrogen does not take them.

Teacher's Note:
1. Example of a hydride: NaH.
2. Metals combine easily with oxygen.

Question 5. Write the observation and the reaction when granulated zinc reacts with dilute sulphuric acid. (2 marks)
Answer:
Bubbles of hydrogen gas are seen coming out. The gas burns with a pop sound.
Zn + dil. H₂SO₄ → ZnSO₄ + H₂
In simple words: Zinc dissolves with bubbling of hydrogen.

Teacher's Note:
1. Zinc is above hydrogen in the series.
2. Test for hydrogen: a burning splinter gives a pop sound.

Question 6. What are the constituents of the alloy solder? Which property of solder makes it suitable for welding electrical wires? (2 marks)
Answer:
Solder is an alloy of lead and tin. Its low melting point makes it suitable for joining electrical wires.
In simple words: Solder is Pb + Sn and melts easily.

Teacher's Note:
1. Low melting point is useful for soldering.
2. Pure lead and tin have different melting points.

Question 7. (i) Select a metal from iron, sodium and magnesium which reacts with hot water but not with cold water. (ii) Write the chemical equation and name the main product formed. (2 marks)
Answer:
(i) Magnesium.
(ii) Mg + 2H₂O → Mg(OH)₂ + H₂. The main products are magnesium hydroxide and hydrogen gas.
In simple words: Magnesium needs hot water; sodium reacts with cold water; iron needs steam.

Teacher's Note:
1. Fe, Al and Zn react only with steam.
2. Magnesium floats on water because of hydrogen bubbles.

Question 8. How are the less reactive metals extracted? Explain with an example. (2 marks)
Answer:
Metals low in the reactivity series are very unreactive. Their oxides can be reduced to the metal by heating alone. For example, cinnabar (HgS) is heated in air to form HgO, and HgO on further heating gives mercury.
2HgS + 3O₂ → 2HgO + 2SO₂; 2HgO → 2Hg + O₂
In simple words: Heat the ore in air and then heat the oxide to get the metal.

Teacher's Note:
1. No reducing agent is needed.
2. Mercury and copper are extracted in this way.

Question 9. Name two metals that catch fire when put in water and say why. (2 marks)
Answer:
Sodium and potassium. They react violently with cold water to form a hydroxide and hydrogen. The reaction is so exothermic that the hydrogen formed catches fire.
In simple words: The heat of the reaction ignites hydrogen.

Teacher's Note:
1. They are kept under kerosene.
2. 2K + 2H₂O → 2KOH + H₂.

Question 10. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction. (2 marks)
Answer:
The pale green colour of the solution fades and becomes colourless, and grey particles of iron are formed.
Zn + FeSO₄ → ZnSO₄ + Fe
In simple words: Zinc displaces iron, so the green colour goes.

Teacher's Note:
1. Zinc is more reactive than iron.
2. Iron(II) sulphate solution is pale green.

Question 11. Name two metals that start floating in water after some time and say why. (2 marks)
Answer:
Calcium and magnesium. They react with water to form hydrogen gas, and the bubbles stick to the surface of the metal and make it light enough to float.
In simple words: Hydrogen bubbles lift the metal.

Teacher's Note:
1. Calcium reacts with cold water and magnesium with hot water.
2. The hydrogen does not catch fire here.

Short Answer Questions (3 Marks)

Question 12. A shining metal M burns with a dazzling white flame and changes to a white powder N. (a) Identify M and N. (b) Write the balanced equation. (c) Does M undergo oxidation or reduction? Justify. (3 marks)
Answer:
(a) M is magnesium and N is magnesium oxide.
(b) 2Mg + O₂ → 2MgO
(c) Magnesium undergoes oxidation, because oxygen is added to it (it loses electrons to form Mg²⁺).
In simple words: Magnesium burns in oxygen and is oxidised.

Teacher's Note:
1. Gain of oxygen is oxidation.
2. Magnesium oxide is a basic oxide.

Teacher's Note:
1. Present the answer as a table.
2. The metal floats because hydrogen bubbles stick to it.

Question 14. Write some physical properties of metals. (3 marks)
Answer:
1. All metals except mercury are solids at room temperature.
2. Metals have a shining surface (metallic lustre).
3. They are malleable and ductile.
4. They are good conductors of heat and electricity.
5. They are sonorous and generally have high density.
6. They are generally hard, except sodium and potassium.
7. They generally have high melting and boiling points, except sodium and potassium (and gallium, caesium).
In simple words: Metals are shiny, hard, malleable, ductile, sonorous and conduct well.

Teacher's Note:
1. Exceptions: mercury is liquid; sodium and potassium are soft.
2. Lead is a poor conductor.

Question 15. What happens when metal oxides are dissolved in water? Write the chemical reactions. (3 marks)
Answer:
Most metal oxides are insoluble in water. Some, such as sodium oxide and potassium oxide, dissolve in water to form alkalis (metal hydroxides).
Na₂O + H₂O → 2NaOH
K₂O + H₂O → 2KOH
In simple words: Soluble metal oxides give alkalis.

Teacher's Note:
1. The solution turns red litmus blue.
2. Calcium oxide also gives calcium hydroxide.

Question 16. Make a list of common metals arranged in the order of their decreasing reactivity. (3 marks)
Answer:
Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Zinc (Zn) > Iron (Fe) > Lead (Pb) > [Hydrogen (H)] > Copper (Cu) > Mercury (Hg) > Silver (Ag) > Gold (Au)
Reactivity decreases from potassium to gold.
In simple words: Potassium is at the top and gold at the bottom.

Teacher's Note:
1. Learn the series with a mnemonic.
2. Hydrogen is included as a reference.

Question 17. (a) What is meant by the reactivity series of metals? (b) Why are metals not equally reactive? Arrange Fe, Ag, Na, Cu and Al in decreasing order of reactivity. (3 marks)
Answer:
(a) The arrangement of metals in the order of their decreasing reactivity is called the reactivity series.
(b) The reactivity of a metal is its tendency to lose electrons. Metals that lose electrons more easily to form positive ions are more reactive, and this tendency differs from metal to metal.
Decreasing order: Na > Al > Fe > Cu > Ag.
In simple words: Metals differ in how readily they lose electrons.

Teacher's Note:
1. Use the series to rank the metals.
2. Sodium is the most reactive here.

Question 18. Describe an experiment to show that copper does not react with dilute HCl. (3 marks)
Answer:
1. Take small pieces of magnesium, zinc, aluminium, iron and copper and clean them with sand paper.
2. Place them in separate test tubes and add about 10 mL of dilute HCl to each.
3. Observe the rate at which bubbles form. It is fastest for magnesium and decreases in the order Mg > Al > Zn > Fe.
4. No bubbles form with copper, so copper does not react with dilute HCl (or dilute H₂SO₄).
In simple words: Bubbles of hydrogen appear with reactive metals but not with copper.

Teacher's Note:
1. Clean the metals with sand paper first to remove the oxide layer.
2. Bubbling rate shows reactivity.

Question 19. (i) Which metals can displace hydrogen from acids? (ii) Which metals cannot? (3 marks)
Answer:
(i) Metals placed above hydrogen in the reactivity series, such as sodium, calcium, magnesium and zinc, are more reactive than hydrogen and displace it from acids.
(ii) Metals placed below hydrogen, such as copper, silver and gold, cannot displace hydrogen from acids.
In simple words: Only metals above hydrogen in the series can displace it.

Teacher's Note:
1. Hydrogen is the dividing line.
2. Write one example of each.