Chapter 4 : Materials - Metals and Non-metals
Important Question Answers Set 1
Q.1. Iron metal reacts slowly with the oxygen and moisture of damp air to form rust. What is rust chemically known? State whether the rust formed is acidic, basic or neutral.
Ans. Rust is iron(III) oxide (Fe2O3). Rust is a basic oxide.
Q.2. A purple coloured non-metal forms a brown solution in alcohol which is applied on wounds as an antiseptic. Name the non-metal.
Ans. Iodine solution is used as an antiseptic.
Q.3. If a metal coin is dropped on hard floor, it produces a ringing sound. What is this property of metals known as?
Ans. The property of metals to produce ringing sound is called sonority.
Q.4. Zinc sulphate forms a colourless solution in water. Will you observe any colour on adding copper turning in it?
Ans. No, displacement reaction does not take place because copper is less reactive than zinc. Hence, copper cannot displace zinc.
Q.5. If you put one end of a rod of a metal in hot water, you feel hot at the other end. What does it mean? What is this property of metals called?
Ans. The given observation means that heat is transmitted from one end to the other. This property of metals is called conductivity.
Q.6. Why are bells made of metals?
Ans. Metals have sonorous property. Hence ringing sound is produced when metal bells are hit by an object.
Q.7. Name the metal
(a) which reacts with dilute hydrochloric acid to produce hydrogen gas.
(b) which does not react with dilute hydrochloric acid.
Ans.
(a) Zinc metal reacts with dilute hydrochloric acid to produce hydrogen gas.
(b) Copper metal does not react with dilute hydrochloric acid.
Q.8. Which liquid metal is used for making thermometers?
Ans. Mercury metal is used for making thermometers.
Q.9. A substance was burnt in air. The white residue obtained was added to water. This water solution turned red litmus into blue. State whether the substance is a metal or a non-metal.
Ans. The substance is a metal. When the substance was burnet in air, metal oxide was formed. Metal oxides are basic in nature and turn red litmus paper into blue.
Q.10. A given non-metal forms sulphuric acid on reacting with nitric acid. Identify the non-metal.
Ans. Sulphur.
S + 6HNO3 → H2SO4 + 2H2O + 6NO2
Sulphur Nitric Acid Sulphuric Acid Nitrogen Dioxide
Q.11. Name one metal and one non-metal which exist in liquid state at room temperature.
Ans. Metal is mercury and non-metal is bromine which exist in liquid state at room temperature.
Q.12. Name the property which enables metals to be drawn into wires.
Ans. The property which allows the metals to be drawn into wires is called ductility.
Q.13. Name two soft metals which can be cut with a knife.
Ans. Metals which can easily cut with a knife
(i) Sodium (ii) Potassium
These are soft metals.
Q.14. Which metal is stored in kerosene?
Ans. Sodium metal is stored in kerosene.
Q.15. Name a non-metal which is kept in water.
Ans. Phosphorus is kept in water.
Q.16. Which non-metal is essential for our life and all living beings inhale it during breathing?
Ans. Oxygen gas is important for our respiratory system.
Q.17. How can you say that metals have a property of sonorousness?
Ans. Metals produce ringing sound, so they are called sonorous.
Q.18. Copper is used to make electric wires. Why?
Ans. Copper is a good conductor of electricity, so electric wires are made up of copper.
Q.19. Name two major non-metals which are present in fertilisers and enhance the growth of plants.
Ans. (i) Nitrogen (ii) Phosphorus
Q.20. Write the nature of non-metal and metal oxides.
Ans. Mostly non-metallic oxides are acidic in nature while metal oxides are basic in nature.
Q.21. Write physical properties of metals.
Ans. Metals are generally solid, hard, ductile, malleable, sonorous, have metallic lustre and are good conductors of heat and electricity.
Q.22. Name two metals which are good conductors of both heat and electricity.
Ans. Copper and aluminium.
Q.23. Ductility is the property of metals. What do you mean by ductility?
Ans. The property of metals by which they can be drawn into wires is called ductility.
Q.24. Which type of materials we used for making fine electrical contacts in sup.er computers and solar cells?
Ans. We use gold and silver metals for making fine electrical contacts in super computers and solar cells.
Q.25. Which non-metal is used to disinfect water?
Ans. Chlorine is used in water purification plants because chlorine has the ability to kill germs.
Q.26. Which of the following metals can displace the other two metals from their salt solutions?
Zinc, iron, copper
Ans. Zinc is most reactive among three and copper is least reactive among three. Reactivity of iron is in between zinc and copper.
Q.27. What happens when a solution of metal oxide is tested with red litmus and blue litmus solutions?
Ans. When metal oxide is tested with litmus solutions, then red litmus changes into blue colour and there is no change in the colour of blue litmus.
Q.28. Some non-metals like phosphorus are kept in water to protect them from atmospheric oxygen. Write the property of non-metals utilised here.
Ans. Non-metals do not react with water.
Q.29. Which metal reacts neither with cold water nor with hot water?
Ans. Iron and zinc neither reacts with cold water nor with hot water but reacts with steam to produce hydrogen gas.
Q.30. Sheela bought a statue made up of copper. To her surprise, it acquired a dull green colour after a couple of months. Explain the reason.
Ans. The green material is a mixture of copper hydroxide [Cu(OH)2] and copper carbonate (CuCO3) formed due to the reaction of copper with moist air. The following is the reaction.
2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3
Moist Air Green Coating
Q.31. We should not store food stuff in container which is made up of metals such as copper, zinc, aluminium, etc. Why?
Ans. Some food stuffs which have acidic nature such as citrus fruits, lemon pickles and curd should not be stored in container made up of metals such as copper, zinc, aluminium and iron. This is because acid present in food stuffs reacts with these metals to produce toxic compounds which cause food poisoning.
Q.32. Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. Give reason.
Ans. Aluminium is a good conductor of electricity. When it is exposed to air, its surface gets covered with thin layer of oxides (Al2O3) which prevents metal underneath from further corrosion.
Q.33. Sheela prepared a blue coloured solution of copper sulphate in beaker A and placed an iron nail in it. Manoj prepared a yellowish green solution of ferrous sulphate in beaker B and placed a copper wire in it. What changes will they observe in the two beakers after an hour?
Ans. In beaker A, a reddish-brown layer of copper will deposit on the iron nail and blue coloured solution of copper sulphate will become yellowish green due to the formation of iron sulphate. This is because iron is more reactive than copper and it displaces copper from its salt solution (copper sulphate solution).
CuSO4 + Fe → FeSO4 + Cu
Blue Yellowish-Green Reddish-Brown
In beaker B, no change is observed because copper being less reactive does not displace iron (more reactive) from ferrous sulphate solution.
Q.34. Explain why copper vessel acquires a dull green coating.
Ans. When a copper vessel is exposed to moist air for a long time, it acquires a dull green coating. The green substance is the mixture of copper hydroxide [Cu(OH)2] and copper carbonate (CuCO3).
2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3
Moist Air Green Coating
Q.35. What happens when samples of metals and non-metals react with acids?
Ans. Metals react with acids to produce salt and hydrogen gas which burns with a 'pop' sound Non-metals do not react with acids.
Copper does not react with dilute hydrochloric acid and dilute sulphuric acid but it reacts with hot and concentrated sulphuric acid, but no hydrogen gas is produced.
Q.36. If a blacksmith beats an iron piece with hammer. Do you think, will it change its shape? If yes, would you expect a similar change in wood-log on beating?
Ans. Yes, iron piece will change its shape as it is a metal. It increases in size and does not break. If a woodlog is beaten, it does not change its shape but it breaks into pieces.
Q.37. The doctor reported iron deficiency in the body. Where is iron present in our body?
Ans. Iron is present in our blood. Red Blood Cells (RBCs) of blood contain a respiratory pigment known as haemoglobin. Each molecule of haemoglobin contains iron atom as its important component.
Q.38. In what form magnesium is found in plants?
Ans. Magnesium is found in plants in the form of ionic salts in chlorophyll. Due to its deficiency, plants are unable to produce enough chlorophyll and as a result, leaves develop yellowish colour.
Q.39. A more reactive metal displaces the less reactive metal from its salt solution. What do you mean by this reaction?
Ans. In a chemical reaction, when a more reactive metal displaces the less reactive metal from its salt solution, it is called displacement reaction, e.g. zinc can displace copper from its copper sulphate solution as zinc is more reactive than copper.
Less reactive metal cannot displace the more reactive metal from its salt solution, e.g. copper cannot displace zinc from its zinc sulphate solution as copper is less reactive than zinc.
Q.40. Explain why zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution.
Ans. Zinc metal can displace copper from copper sulphate solution as zinc is more reactive than copper. But copper cannot displace zinc from zinc sulphate solution because copper is less reactive than zinc.
Q.41. Shashi bought new flower vase made of copper. After few months, she found that copper vase has lost its lustre and there was a greenish deposit on its surface. Shashi was confused that it is not of pure copper but her friend Rakhi advised her to wash it with tamarind or lemon juice to get the lustre back. She followed the advice and get the lustre of copper vase back. Read the following passage and answer the following questions.
(a) Why does copper vase lose shine so soon after use?
(b) Does copper vessel also get rusted? Explain.
Ans.
(a) The copper objects lose their shine after sometime due to the formation of green coating of basic copper carbonate on its surface. When a copper object remains in damp air for a considerable time, then copper reacts slowly with the carbon dioxide, water and air, it acquires a dull appearance.
(b) Yes, copper vessel also gets rusted. The formation of green coating on the surface of a copper object corrodes it. The green material is a mixture of copper hydroxide, Cu(OH)2 and copper carbonate, CuCO3. The following is the reaction
2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3
Moist Air Green Coating
Q.42. Shikha bought a new iron container and kept blue copper sulphate solution in it. Next day, she found that blue colour of copper sulphate solution fades and iron container becomes porous. She went to the shopkeeper and complaint that iron container is not of good quality. But the shopkeeper argued that container is of good quality and he is not giving her money back. By chance, her friend Mohan came there and asked the matter, and told that the container is of good quality and you have kept the wrong substances in it, so fault is all yours. On the basis of the above passage answer the following questions. Why the container becomes porous when blue copper sulphate solution is kept in it?
Ans. The container becomes porous when blue copper sulphate solution is kept into it because iron being more reactive displaces copper from copper sulphate solution and itself form green coloured ferrous sulphate.
Q.43. Metals are malleable and ductile. They possess such properties which make them useful for a number of purposes, e.g. in making coins, jewellery, electrical wires, etc. For different requirements, different metals are used. It depends on the nature of metals. Now give the answer of the following questions.
(a) Give two reasons why gold is used in making jewellery?
(b) If you have to select the metal among copper, aluminium and silver for the transmission of electricity, which one would you prefer and why?
(c) Between silver and copper, which is the better conductor of heat?
(d) Generally, silver foils are used for the decoration of sweets. Are they harmful for us? If yes, then in what manner?
Ans.
(a) Firstly, gold is highly malleable and ductile. Secondly, it is inert towards chemical reactions and is not attacked by the gases present in air.
(b) We prefer copper wire because it is the better electrical conductor than aluminium. However, silver is the best electrical conductor but it is very expensive.
(c) Silver is the better conductor of heat than copper.
(d) Yes, they are harmful for us because they affect throat and lungs.
Q.44. Iron is more reactive than copper. Can you write an activity to show this?
Ans. Take about 50 ml of water in a beaker and dissolve 5 g of copper sulphate in it to obtain copper sulphate solution (which is blue in colour). Put a clean iron nail in this solution and keep the beaker undisturbed for some time.
We will find that the blue colour of copper sulphate solution starts fading gradually and the iron nail gets covered with a red-brown layer of copper metal. It is because iron is more reactive than copper, so it displaces copper metal from its solution of copper sulphate. It is the copper metal set free from its compound which forms a red-brown layer on the surface of iron nail. This shows that iron is more reactive than copper.
Copper sulphate + Iron → Iron sulphate + Copper
(Blue solution) (Grey) (Greenish solution) (Red- brown)
Q.45. What happens when metals and non-metals react with oxygen separately? What is the nature of the products formed? Explain with examples. Give test also to check the nature of products formed.
Ans.
Metals reaction with Oxygen:
Metals react with oxygen and form metal oxides which are basic in nature. Basic metal oxides turn red litmus into blue.
Metal + Oxygen → Metal oxide (basic)
In processes such as the rusting of iron and burning of magnesium ribbon, oxide formation takes place.
Magnesium + Oxygen → Magnesium oxide
(Mg) (O2) (MgO)
Magnesium oxide dissolves partially in water to form magnesium hydroxide solution which is a base.
Magnesium oxide + Water → Magnesium hydroxide (Base)
(MgO) (H2O) Mg(OH)2
Magnesium hydroxide turns red litmus into blue showing that it is a base and magnesium oxide is a basic oxide. Similarly, the reaction of iron metal with oxygen in the presence of water can be written as:
Iron + Oxygen + Water → Iron oxide (rust)
(Fe) (O2) (H2O) (Fe2O3)
From Air (Basic Oxide)
When a copper vessel is exposed to moist air for long time, it acquires a dull green coating. The green material is a mixture of copper hydroxide [Cu(OH)2] and copper carbonate [CuCO3].
2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3
Moist Air Green Coating
This is the corrosion of copper.
Non-metals reaction with Oxygen:
Non-metals react with oxygen to form non-metal oxides which are acidic in nature.
Non-metal + Oxygen → Non-metaloxide (Acidic)
The acidic non-metal oxides turn blue litmus to red.
Q.46. Aluminium is one of the most widely used metal. It is used for various purposes like in making automobile parts, electrical wires, utensils, toys, household articles, etc. It is also used for welding broken parts of iron machinery. Now, give the answer of the following questions.
(a) Iron and aluminium both react with oxygen. Why aluminium is considered better than iron for a number of purposes?
(b) Give two examples where you have seen the use of aluminium foils.
(c) Why aluminium is used in making cooking utensils?
Ans.
(a) Attack of oxygen and moisture on the surface of iron makes rust which does not stick to the surface of iron. It peels off easily exposing fresh surface for rusting. But attack on aluminium surface forms an oxide layer which protects the surface from further attack.
(b) In wrapping of food stuff and in wrapping of medicinal tablets.
(c) Aluminium is used in making cooking utensils because aluminium is a good conductor of heat.
Q.47. A doctor prescribed a tablet to a patient suffering from iron deficiency. The tablet does not look like iron. Explain.
Ans. Iron is a metal but the tablet is not made up of iron metal. It is made up of a salt of iron. So, it does not look like iron.