Lakhmir Singh & Manjit Kaur: Materials Metals And Non-Metals- 2 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.31. Name the non-metal used to make purple coloured solution which is applied on cuts and wounds as an antiseptic.

Iodine is used to make purple coloured solution which is applied on cuts and wounds as an antiseptic. It is used in the treatment and prevention of wound infection.

Q.32. Name two non-metals which are used in fireworks (crackers, etc.)

Sulphur and sodium are used in fire crackers. Fireworks contains metal salts and metal oxides which react to produce an array of colours.

Q.33. Which non-metals is used as a fuel?

Carbon is used as a fuel in the form of coke or charcoal.

Q.34. State whether the following statements are true or false?
(a) All metals exist in solid form at room temperature.
(b) Coal can be drawn into wires.
(c) Non-metals react with dilute acids to produce hydrogen gas.
(d) Sodium is a very reactive metal.
(e) Copper displaces zinc from zinc sulphate solution.
(f) Rust formed on iron objects is basic in nature.
(g) Non-metals react with water to form a gas which burns with a ‘pop’ sound.

(a) False
The metal which is liquid at room temperature is Mercury(Hg). Another metal called Gallium also exists as liquid at room temperature.
(b) False
Coal is made up of carbon. Carbon is a nonmetal. It is non-malleable and non-ductile; hence, coal cannot be drawn into wires.
(c) False
Metals react with dilute acids to form metallic salts and hydrogen gas. For example, zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas.
(d) True
Sodium is a very reactive metal. It can even react with the moisture in the air. The reaction of sodium with water is exothermic. It produces a lot of heat.
(e) False
Copper is less reactive than zinc. It is placed below zinc in the reactivity series of metals. Hence, copper cannot displace zinc from zinc sulphate solution.
(f) True
Rust is a chemically known as iron oxide. Metal oxides are basic in nature. Since, rust is a metal oxide, it will be basic in nature.
(g) False
Metals react with water to produce hydrogen gas. For example, sodium reacts with water to form sodium hydroxide and hydrogen gas.

Q.35. Fill in the following blanks with suitable words:
(a) Metals are ______ conductors of heat and ______
(b) Most non-metals are ______ conductors of heat and electricity.
(c) Phosphorous is a very ______ Non-metal.
(d) Metals react with acids to produce ______ gas.
(e) Iron is more ______ than copper.
(f) Metals form ______ oxides whereas non-metals form ______oxide.
(g) Sulphur forms ______ oxide whereas magnesium forms _____ oxide.
(h) A non-metal is used to make an antiseptic solution called tincture ______

(a) good; electricity
Metals are used to make wires because they are good conductors of electricity. Due to good conductors of heat, metals are used to make utensils.
(b) poor
Non- metals do not have free electrons; hence, they are non-conductors of heat and electricity.
(c) reactive
Phosphorus cannot be kept open in the air because it combines with oxygen so easily that it catches fire automatically. For safety, phosphorus is stored under water in chemical laboratories.
(d) hydrogen.
Metals react with dilute acids to form metallic salts and hydrogen gas. For example, zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas.
(e) reactive
Iron is more reactive than copper. For example, if we put Iron nail into copper sulphate solution. Iron nail will displace copper from copper sulphate solution.
(f) basic; acidic
Metallic oxides are basic because they react with water to form bases. Nonmetals react with oxygen to form nonmetallic oxides which are acidic in nature because they react with water to form acids.
(g) acidic; basic
Metallic oxides are basic because they react with water to form bases. Nonmetals react with oxygen to form nonmetallic oxides which are acidic in nature because they react with water to form acids.
(h) iodine
Iodine is used to make purple coloured solution which is applied on cuts and wounds as an antiseptic. It is used in the treatment and prevention of wound infection.

Q.36. State two physical properties on the basis of which metals can be distinguish from non-metals.

The two physical properties on the basis of which metals can be distinguished from non-metals are Malleability and Ductility.
The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling.
The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires. For example, Aluminium and copper are examples of highly ductile metals.

Q.37. Name the gas produced when aluminium foil reacts with:
(a) dilute hydrochloric acid.
(b) Sodium Hydroxide solution.

When aluminium foil reacts with sodium hydroxide, sodium aluminate is formed. Metals react with dilute acids to form metallic salts and hydrogen gas. For example, Aluminium foil reacts with dilute hydrochloric acid to produce aluminium chloride and hydrogen gas.
The balanced chemical equation for the reaction is:
2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g).
Aluminium is an amphoteric metal. It reacts with both acids and bases. The reaction is highly exothermic and produces a lot of heat. There is rapid evolution of hydrogen gas during this reaction.

Q.38. State any two physical properties for believing that aluminium is a metal.

Aluminium is highly malleable and ductile. Due to this property, aluminium is used in the production of utensils and wire. Aluminium is a good conductor of heat which makes it ideal for making utensils.

Q.39. Compare the properties of metals and nonmetals with respect to:
(i) malleability
(ii) ductility and
(iii) conduction of heat and electricity

The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling.
The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires. For example, Aluminium and copper are examples of highly ductile metals.
Metals have free electrons which makes them good conductors of heat and electricity. Non- metals do not have free electrons, hence, they are nonconductors of heat and electricity.

Q.40. Give reason why.
(a) Copper metals used for making electric wires.
(b) Graphite is used for making electrode in a cell.
(c) Immersion rods for heating liquids are made of metallic substances.

(a) Copper metal is used for making electric wires because it is highly ductile in nature. It is a good conductor of electricity.
The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires. Metals have free electrons which makes them good conductors of heat and electricity.
(b) Graphite is a good conductor of electricity. Graphite is made of carbon. Its valence electrons are free to move. As a result, graphite is able to conduct electricity which makes it useful for making electrode in a cell.
(c) Immersion rods for heating liquids are made of metallic substances because metallic substances are good conductors of electricity and heat. Metals have free electrons which makes them good conductors of heat and electricity.

Q.41. Define (a) malleability, and (b) ductility.

(a) Malleability: The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling.
(b) Ductility: The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires.

Q.42. What is meant by saying that metals are:
(i) Malleable
(ii) Ductile
(iii) Lustrous and
(iv) Sonorous

(i) The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling. For example, aluminium due to its high ductility, it can be changed into thin sheets to make aluminium foil.
(ii) The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires. For example, Copper metal is used for making electric wires because it is highly ductile in nature.
(iii) Metals have quality to reflect light. As a result, metals are lustrous in nature. It makes metals attractive due to their luster and rarity. Hence, metals like, gold and silver are used to make jewellery. These metals do not tarnish or react with air.
(iv) Metals are sonorous because they produce a unique sound when something hard strikes their surface. As a result, metals are used in making bells or gongs.

Q.43. There are two boxes, one made of metal and the other made of wood, which are similar in appearance. How will you find out which box is made of metal?

The box made of metal can be identified by striking hard on its surface. Metals are sonorous because they produce a unique sound when something hard strikes their surface. The box which is made of metal will produce a sound on striking its surface.

Q.44. Consider the following materials:
Copper, Sulphur, Phosphorus, Carbon (such as: pencil lead), Gold, Silver: Which of these materials are: Malleable and ductile; and brittle.

Copper, gold and silver are Malleable and ductile because these are metals. The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling. The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires. All of these metals can be used to make wires and sheets.
Sulphur, phosphorous and carbon are brittle. These are nonmetals and cannot be rolled into wires or drawn into sheets.

Q.45. Can you hold a hot metallic pan which is without a plastic or a wooden handle? Give reason for your Answer:.

It is difficult to hold a metallic pan without a plastic or wooden handle. This is because it will result into burning of fingers or hand due to high heat. If the metallic pan has a wooden handle, it will help to hold it. Wood is made of nonmetal which is a poor conductor of heat. Hence, wooden handle is very useful in metallic pan.

Q.46. The screw driver used by an electrician has a plastic or wooden handle. Why?

Screwdriver is made of metal which is a good conductor of electricity. In order to prevent electric shocks by the screw driver its handle is made of wood. Wood is a poor conductor of electricity which protects from electric shocks and makes the screw driver safe from electric shocks.

Q.47. What is the nature (acidic/basic) of the following oxides?
(a) Magnesium oxide
(b) Sulphur dioxide
Given reason for your choice.

Magnesium is a metal. Metals react with oxygen to form metallic oxides. These Hence, Magnesium oxides are basic in nature. On the other hand, nonmetals react with oxygen to form nonmetallic oxides. These oxides differ from metallic oxides because they are acidic in nature. Nonmetallic oxides react with water to form acids. Therefore, Sulphur dioxide is acidic in nature. Magnesium oxide is basic in nature.

Q.48. What type of oxides are formed:
(a) when metals combine with oxygen?
(b) when non-metals combine with oxygen?

(a) Metals react with oxygen to form metallic oxides. These metallic oxides are basic because they react with water to form bases. For example, Magnesium is a metal and magnesium oxide is basic in nature.
(b) Nonmetals react with oxygen to form nonmetallic oxides. These oxides differ from metallic oxides because they are acidic in nature. Nonmetallic oxides react with water to form acids. For example, Sulphur is a nonmetal. Sulphur dioxide is acidic in nature.

Q.49. Element A is soft, brittle and does not conduct electricity. Element B is hard, malleable and ‘ductile; and also conducts electricity. Which of the two elements, A or B, is a non-metal?

Element A is a nonmetal. Since, it is soft and brittle in nature.
Element B is a metal because it is malleable and ductile and it also conducts electricity. The property of metals which allows metals to be hammered into thin sheets is called Malleability. Due this unique property, metals can be flattened into thin sheets by hammering and rolling. The property of metals which enables them to be drawn into wires is called Ductility. Due to this property metals can be stretched without breaking and drawn into thin wires. All of these metals can be used to make wires and sheets.

Q.50. Consider the following elements:
Sodium, Sulphur, Carbon, Magnesium
Which of these elements will form:
(a) acidic oxides.
(b) Basic oxides.

(a) Carbon and Sulphur will form acidic oxides. Nonmetals react with oxygen to form nonmetallic oxides. These oxides differ from metallic oxides because they are acidic in nature. Nonmetallic oxides react with water to form acids. Therefore, oxides of sulphur and carbon i.e. sulphur dioxide and carbon dioxide are acidic in nature.
(b) Sodium and magnesium oxides will be basic in nature. Metals react with oxygen to form metallic oxides. These metallic oxides are basic because they react with water to form bases.

Q.51. What happens when a copper vessel is exposed to moist air for a long time?

When copper vessel is exposed to moist air for a long time it develops a green layer on its surface. Copper corrodes by oxidation in which it reacts with oxygen in the air to form copper oxide. Copper oxide then combines with carbon dioxide to make copper carbonate, which gives it a green colour. This process is called corrosion of copper.

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

Q.52. When a copper object is exposed to moist air for a long t e, then a green coating is formed on its surface.
(a) What is the material of the green coating?
(b) State whether the green coating is acidic or basic.

(a) When copper vessel is exposed to moist air for a long time it develops a green layer on its surface. Copper corrodes by oxidation in which it reacts with oxygen in the air to form copper oxide. Copper oxide then combines with carbon dioxide to make copper carbonate, which gives it a green colour. This process is called corrosion of copper. 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
(b) The green coating will be basic in nature. Green coating is made of copper oxide which is an oxide of metal. Metals react with oxygen to form metallic oxides. These metallic oxides are basic because they react with water to form bases.

Q.53. Sodium metal reacts vigorously with water.
(a) Name the gas evolved when sodium reacts with water.
(b) State whether the solution formed by the reaction of sodium with water is acidic or basic.

(a) Metals react with water to produce hydrogen gas. Sodium reacts with water to form sodium hydroxide and hydrogen gas. Sodium is a highly reactive metal. It even reacts with the moisture present in air. The reaction of sodium with water is highly exothermic in nature. It produces a lot of heat energy and this heat energy can cause the hydrogen gas produced during the reaction, to catch fire. In order to keep it safe, sodium metal is stored in kerosene.
(b) Metals reacts with water to form metal hydroxides and hydrogen gas. These metallic hydroxides are basic. Sodium reacts with water to form sodium hydroxide and hydrogen gas. Sodium hydroxide is basic in nature.

Q.54. How do metals react with dilute acids? Explain with the help of an example.

Metals react with dilute acids to form metallic salts and hydrogen gas. For example, Aluminium foil reacts with dilute hydrochloric acid to produce aluminum chloride and hydrogen gas.

The balanced chemical equation for the reaction is:

2Al(s) + 6HCl(aq) 2AlCl₃(aq) + 3H₂(g).

Q.55. What would you observe when a strip of zinc is placed in copper sulphate solution? Write a word equation of the reaction which takes place.

When a strip of zinc is placed in copper sulphate solution it will displace copper from copper sulphate solution. Zinc is placed above copper in reactivity series of metal. Hence, it will be able to replace copper from copper sulphate solution.

Zinc + Copper Sulphate ➝ Copper + Zinc sulphate

Q.56. Can copper displace iron from iron sulphate solution? Give reason for your answer.

Copper cannot displace iron from iron sulphate solution. Copper is less reactive than iron. Iron is placed above the copper in reactivity series of metals. Therefore, copper cannot displace iron from iron sulphate solution. But if we put Iron nail into copper sulphate solution. Iron nail will displace copper from copper sulphate solution.

Q.57.
(A) Name one metal which can displace iron from iron sulphate solution.

Zinc is placed above iron in the reactivity series of metals. Hence, zinc will be able to displace iron for iron sulphate solution.

(B) Name one metal which cannot displace iron from iron sulphate solution.

Copper cannot displace iron from iron sulphate solution. Copper is less reactive than iron. Iron is placed above the copper in reactivity series of metals. Therefore, copper cannot displace iron from iron sulphate solution.

Q.58. Can you store lemon pickle in an aluminium utensil? Explain.

Lemon pickle is acidic in nature. Aluminium metal is highly reactive in nature. If the pickle is stored in an aluminium container, the acid present in pickle will react with aluminium and the pickle will be spoiled.
Hence, we cannot store lemon pickle in aluminium container.

Q.59. Why should the foodstuffs like orange juice, pickles, chutney and curd not be kept in iron or aluminium containers?

Food stuff like orange juice, pickles, chutney and curd are acidic in nature. Iron and aluminium are highly reactive metals. If any of this stuff is stored in iron or aluminium container the acid inside these food stuffs will react with iron or aluminium to produce toxins. Hence, we cannot store foodstuffs like orange juice, pickles, chutney and curd not be kept in iron or aluminium containers.

Q.60. Give reasons for the following:
(a) Sodium and potassium are stored in kerosene.
(b) Copper cannot displace zinc from its salt solution (zinc sulphate solution).

(a) Metals react with water to produce hydrogen gas. Sodium reacts with water to form sodium hydroxide and hydrogen gas. Similarly, potassium also reacts with water to potassium hydroxide and hydrogen gas. Both Sodium and potassium are highly reactive metals. They can even react with the moisture present in air. The reaction of sodium and potassium with water is highly exothermic in nature. It produces a lot of heat energy and this heat energy can cause the hydrogen gas produced during the reaction, to catch fire. In order to keep it safe, sodium and potassium are stored in kerosene.
(b) Copper cannot displace zinc from zinc sulphate solution. Zinc is placed above copper in reactivity series of metal. Hence, it will be able to replace copper from copper sulphate solution.
Zinc + Copper Sulphate ➝ Copper + Zinc sulphate