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Q1. (a) What is a saucer pan made of? Why? (b) A saucer pan has plastic handles. Why?

Solution

(a) Saucer pan is made of metals because metals are good conductors of heat. (b) Plastics are bad conductor of heat and do not get heated. Thus, to prevent burning of hands, a saucer pan has plastic handles.

Q2. Which property of metals makes them suitable for use in jewellery?

Solution

Two properties of metals makes them suitable for use in jewellery: (a) Metals have a shiny lustre. (b) Metals are malleable and ductile.

Q3. Explain an experiment by taking a suitable example to show that oxides of metals are basic in nature.

Solution

We take a metal-oxide e.g. magnesium oxide in a test tube. Now we add a little water it and shake it. We will divide this solution in two parts and test it with blue litmus paper and red litmus paper. When we dip blue litmus paper to one of the test tubes containing magnesium oxide solution then there is no change in colour. When we dip red litmus paper to another test tube containing magnesium oxide solution then we see that red litmus paper turns blue. We know that only basic substances turn red litmus to blue. Since magnesium oxide solution turns red litmus to blue, therefore, it is basic in nature.

Q4. Taking sulphur, with the help of an acitivity, show that non-metal oxides are acidic in nature and turn blue litmus to red.

Solution

Non-metals react with oxygen to form oxides. Sulphur is a non-metal. We take a small amount of sulphur powder in a deflagrating spoon and heat it over a flame. As soon as sulphur starts burning with a blue flame, we introduce the deflagrating spoon in a gas jar and allow the sulphur to burn inside the gas jar. Cover the gas jar with a lid to prevent the gas being formed from escaping. Sulphur burns in the air of gas jar to form a pungent smelling gas (sulphur dioxide). Remove the deflagrating spoon from the gas jar. We now put some water in the gas jar, cover it with a lid and shake it to dissolve sulphur dioxide gas. Add some blue litmus solution to the gas jar. We will see that the blue litmus solution turns red. This shows that sulphur dioxide gas is acidic in nature (because only acidic substances turn blue litmus to red). From this activity we conclude that sulphur is a non-metal which forms an acidic oxide (sulphur dioxide) on burning in air.

Q5. You are given some substances. Just by looking can you classify those as metals and non-metals? Which physical property will you be using to classify?

Solution

Yes, we can classify as metals and non-metals based on lustre. Metals have a shiny lustre while non- metals generally do not have a shiny lustre.

Q6. (i) Why is graphite used for making electrodes? (ii) Why is iron used in constructing bridges and machineries? (iii) Why are metals used for making strings of a guitar?

Solution

(i) Graphite is used for making electrodes since it is a good conductor of electricity. (ii) Iron is used in construction of bridges and machineries because it is very strong that it can hold large weights without breaking. (iii) Metals are used for making strings of guitars as they are capable of producing a ringing sound or due to the property of sonority.

Q7.   Phosphorus is stored in water. Give reason.

Solution

Phosphorus is a very reactive non-metal and catches fire when exposed to air. So in order to protect phosphorus from atmospheric air, it is stored in water.

Q8. (i) Name a non-metal which is used to disinfect drinking water and which property makes it suitable for this? (ii) A purple colour liquid of a non-metal is applied on wounds as antiseptic. Name that non-metal.

Solution

(i) Chlorine is used to disinfect drinking water as it has the ability to kill germs. (ii) Iodine is a non-metal which is used as antiseptic for skin treatment.

Q9. Name  a non-metal which exists in liquid state.

Solution

Bromine

Q10. (i) Name the reaction in which a more reactive metal displaces the less reactive metal from its compound in aqueous solution. (ii) Can reaction of iron metal with zinc sulphate solution be the example of such reaction? Give reason for your answer.

Solution

(i) Displacement reaction. (ii) No, reaction of iron metal with zinc sulphate solution be the example of such reaction. Since iron metal is less reactive than zinc, therefore, it cannot displace zinc from its solution of zinc sulphate.

Q11. Why are metals used for making electric cables?

Solution

Metals are good conductors of electricity and are ductile i.e. can be drawn into thin wires hence they are used for making wires.

Q12. Which property of iron metal is utilized in making iron sheets required for making buckets? Why iron is used?

Solution

Iron being a metal is highly malleable i.e. it can be easily hammered into thin sheets. Iron is hard and strong hence iron is preferred.

Q13. (i) Name the metal which is used for decorating sweets and which property makes it suitable for this? (ii) Write another use of this metal.

Solution

(i) Silver foils are used for decorating sweets. It is because of its high malleability, silver metal can be hammered into thin silver sheets. (ii) Silver metal is used for making jewellery.

Q14. Why is chlorine used in water purification plants?

Solution

Since chlorine has the ability to kill germs, it is used in water purification plants.

Q15. Cu + AgNO₃ → CuNO₃ + Ag Fe + CuSO₄ → FeSO₄ + Cu Zn + FeSO₄ → ZnSO₄ + Fe From above information arrange the given metals in increasing order of reactivity. Give reason for your choice.

Solution

Since zinc displaces iron, it is more reactive than iron but iron displaces copper therefore iron comes above copper in reactivity series. Similarly, copper displaces silver that is silver is least reactive. Ag < Cu < Fe < Zn

Q16. Name: (a) A metal which is liquid at room temperature. (b) Two metals which are soft and can be cut with a knife.

Solution

(a) A metal which is liquid at room temperature :- Mercury (b) Two metals which are soft and can be cut with a knife :- Sodium and potassium

Q17. Name the metal which is used in mining drills and which property makes it suitable for this?

Solution

Tungsten is the metal which is used in mining drills because it has high melting point and it is very hard.

Q18. Name two common metals which react with bases to produce hydrogen gas.

Solution

Aluminium and zinc are the two common metals which react with bases to produce hydrogen gas.

Q19. Name any two non-metals whose crystals are lustrous.

Solution

Iodine and graphite.

Q20. Why metals are used in making machineries?

Solution

Metals are used in making machineries because they are strong, hard and rigid and have high melting and boiling points.

Q21. Why is sodium stored in kerosene?

Solution

Sodium reacts violently with cold water to form sodium hydroxide solution along with the evolution of hydrogen gas. 2Na     + 2H₂O  →  2NaOH + H₂ Since, sodium reacts vigorously with the oxygen and water producing a lot of heat, it is stored in kerosene.

Q22. (i) Give name of two metals which are used for making frying pans and geysers. Which property makes them suitable for making utensils and water boilers? (ii) Name a metal which is a poor conductor of heat.

Solution

(i) Copper and aluminium are used for making frying pans and geysers because they are very good conductors of heat. (ii) Lead is a poor conductor of heat.

Q23. Coal and pencil lead cannot be drawn into wires. In which category will you place them? Metals or non-metals?

Solution

They are non-metals since non-metals are brittle and non ductile. So, they cannot be drawn into wires.

Q24. (i) Why does the colour of iron sulphate solution change when zinc is added to the solution? (ii) What change in colour is observed?

Solution

(i) Zinc is more reactive than iron. Therefore, when zinc is added to the solution of iron sulphate, the colour of iron sulphate solution changes. It is because zinc displaces iron from its solution of iron sulphate and a grey precipitate of iron and a colourless solution of zinc sulphate is formed. (ii) Green colour of iron sulphate solution will fade away and colourless solution with grey precipitate will be formed.

Q25. Name the metal used in nuclear reactors and aerospace projects.

Solution

Aluminium

Q26. Name one non-metal which conducts electricity.

Solution

Graphite.

Q27. Iron metal cannot displace a more reactive zinc metal from zinc sulphate solution.

Solution

ZnSO₄ + Fe  → No displacement reaction The displacement reaction does not occur because iron metal is less reactive than zinc metal. So, a less reactive iron metal cannot displace a more reactive zinc metal from zinc sulphate solution.

Q28. (i) How do non-metals react with acids? (ii) Which gas is emitted when metals react with acids?

Solution

(i) Non-metals do not react with acids. (ii) Hydrogen gas is liberated when metals react with acids.

Q29. Name a metal which is used in making mirrors. Which property makes it suitable for this?

Solution

Silver metal is used in making mirrors. Due to shiny appearance silver metal is an excellent reflector of light.

Q30. Mention some uses of non-metals.

Solution

Uses of non-metals: Oxygen is essential for our life which all living beings inhale during breathing. Nitrogen is used in fertilizers to enhance the growth of plants. Chlorine is used in water purification process. Iodine solution is applied on wounds as an antiseptic.

Q31. X + YSO₄ → XSO₄+ Y Y + XSO₄ → No reaction Explain the reason for the above:

Solution

'X' is more reactive than 'Y' hence 'X' is able to displace 'Y' from its salt whereas 'Y' is not able to displace 'X' from its salt because it is less reactive than 'X'.

Q32. Give reasons for the following: (a) Aluminum foils are used to wrap food items. (b) Immersion rods for heating liquids are made up of metallic substances.

Solution

(a) Aluminum foils are used to wrap food items because aluminum metal is malleable. Therefore, it can be beaten into thin foils. (b) Metals are good conductors of heat and electricity. Therefore, immersion rods for heating liquids are made of metallic substances.

Q33. How does aluminium react with sodium hydroxide?

Solution

Aluminium reacts with sodium hydroxide to form salt and hydrogen gas. Aluminium + NaOH  →    NaAlO₂      +    H₂

Q34. Bells are made up of metals. Why?

Solution

Metals are sonorous. They produce sound when hit. Therefore bells are made of metals.

Q35. Aluminium is used in the form of thin foils for packaging. Give reason.

Solution

Since aluminium is highly malleable, it is used in the form of thin foils for packaging.

Q36. (i) Why does copper coin dissolve in the solution of silver nitrate if it is immersed in it for some time? (ii) What colour change is observed?

Solution

(i) Copper is more reactive than silver. Therefore, when copper coin is kept immersed in a solution of silver nitrate, it will displace silver from silver nitrate solution and a solution of copper nitrate will be formed. Thus, copper coin will dissolve in the solution. (ii) The colour of the solution will change from colourless to blue.

Q37. (a) What happens when calcium reacts with cold water?(b) Why does calcium metal starts floating in water after the reaction?

Solution

(a) Calcium reacts with cold water to form calcium hydroxide along with evolution of hydrogen gas.(b) The piece of calcium metal starts floating in water because the bubbles of hydrogen gas formed during the reaction stick to its surface.

Q38. (i) Copper is used for making electric wires. But how do metals conduct electricity? (ii) Which metal is the best conductor of electricity?

Solution

(i) Metals offer very less resistance to the flow of electric current. They conduct electricity because of the presence of free electrons in them. These free electrons can move easily through the metal and thus conduct electricity. (ii) Silver is the best conductor of electricity.

Q39. How do non-metals react with water?

Solution

Non-metals do not react with water though they may be very reactive in the air.

Q40. What is the nature of metallic and non-metallic oxides?

Solution

Metallic oxides are basic in nature and non-metallic oxides are acidic in nature.