NCERT Solutions for Class 8 Science Chapter 4 Materials Metals and Non Metals

NCERT Solutions for Class 8 Science Chapter 4 Materials Metals and Non Metals

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NCERT Solutions for Class 8 Science Chapter 4 Materials Metals and Non Metals

Subjective Questions
1 Mark

Question 1.
Non-metals cannot be drawn into wires. Why ? [DAV2008]
Answer:
Non-metals are not ductile, therefore they cannot be drawn into wires.

Question 2.
Complete the following equation :
Zn + 2HCl ——-> __+ __   [MSE (Chandigarh) 2007]
Answer:
Zn + 2HCl ——-> ZnCl₂ + H₂

Question 3.
Which of the following can be beaten into thin sheets ? [NCERT]

• Zinc
• Phosphorus
• Sulphur
• Oxygen.

Answer:
Zinc.

Question 4.
The number of metals is much ………….. than non-metals.
Answer:
More.

Question 5.
……… are the good conductors of heat and electricity.
Answer:
Metals.

Question 6.
Examples of metals are ………., ……. and ………
Answer:
Iron, sodium and nickel.

Question 7.
Examples of non-metals are ………. , …….. and …….
Answer:
Sulphur, chlorine and oxygen.

Question 8.
Explain the term ‘metallurgy’.
Answer:
Metallurgy is the science of extracting metals from their ores and purifying them for various uses.

Question 9.
State general steps involved in metallurgy of a metal.
Answer:
The general steps of metallurgy are :

• Concentration of ore.
• Reduction of the metal compound.
• Refining of metal.

Question 10.
Metals are (softer/harder) than non-metals.
Answer:
Harder.

Question 11.
Most non-metals are (bad/good) conductors of heat.
Answer:
Bad.

Question 12.
The property that allows the metals to be hammered into thin sheets is called (ductility/ malleability).
Answer:
Malleability.

Question 13.
Melting point of most non-metals is (higher/lower) than metals.
Answer:
Lower.

Question 14.
(Metals/non-metals) display lustre.
Answer:
Metals.

Question 15.
Arrange the following metals in the order of their decreasing chemical activity : magnesium, potassium, iron, gold.
Answer:
Potassium, magnesium, iron, gold.

Question 16.
Can copper displace iron from iron sulphate solution ? Give reasons.
Answer:
Copper cannot displace iron from iron sulphate because copper is less reactive than iron.

Question 17.
(Platinum/iron) is the member of the family of noble metals.
Answer:
Platinum.

Question 18.
Pure gold is (24/100) carats.
Answer:
24.

Question 19.
International standards of weights are made of (gold-silver/platinum-iridium) alloy.
Answer:
Platinum-iridium.

Question 20.
Gold dissolves in (aqua regia/aqueous solution of silver nitrate).
Answer:
Aqua regia.

Question 21.
Silver tarnishes due to (nitrogen oxides/hydrogen sulphide) in the air.
Answer:
Hydrogen sulphide.

Question 22.
Why is aluminium used in making aeroplanes ?
Answer:
Aluminium is used in making aeroplanes, as it is light and has high resistance to corrosion when exposed to air which aircrafts demand the most.

Question 23.
What type of oxides are formed by metals ?
Answer:
Metals form basic oxides.

Question 24.
What type of oxides are formed by non-metals ?
Answer:
Non-metals form acidic or neutral oxides.

Question 25.
How does phosphorus occur in nature ?
Answer:
Phosphorus occurs in nature in the combined state as it has strong affinity for oxygen.

Question 26.
Give the different forms of silica in nature.
Answer:
Silica occurs in nature as ordinary sand, flint, quartz and opal.

Question 27.
Which metal foil is used in packing of some medicine tablets ?
Answer:
Aluminium.

Question 28.
Name the soft metal which can be cut with a knife.
Answer:
Sodium or potassium.

Question 29.
Name the non-metal used in vulcanization.
Answer:
Sulphur.

Question 30.
Name one metal which is not malleable.
Answer:
Zinc or arsenic.

Question 31.
Name one non-metal which has lustre.
Answer:
Graphite or Iodine.

Question 32.
What would happen to iron railings if they are not painted ?
Answer:
They will get rusted.

Question 33.
Name the element commonly used for converting edible vegetable oils into vanaspati ghee.
Answer:
Hydrogen.

Question 34.
Name the element used for making containers of dry cells.
Answer:
Zinc.

Question 35.
Which metal is used for making radiators of cars ?
Answer:
Copper.

Question 36.
Name the metal whose salt is used for making photographic films.
Answer:
Silver.

2 Marks

Question 1.
White phosphorous has to be kept in water. Why ? [NCT2007]
Answer:
Phosphorus is to be kept in water to prevent its contact with air because it is highly reactive.

Question 2.
Can you store lemon pickle in an aluminium utensils ? Explain. [NCERT]
Answer:
We cannot store acidic food stuffs in aluminium utensils because aluminium reacts with acids. The food gets spoilt.

Question 3.
One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight ? [NCERT]
Answer:
The goldsmith must have used acid to clean the gold jewellery and some gold must have dissolved in it. Therefore, there was loss in weight of the jewellery.

Question 4.
Write short notes on

1. Metallurgical processes
2. Uses of common metals and non-metals
3. Noble metals

Answer:

1. Metallurgical process can be divided into following steps :
   • Concentration of the ore
   • Reduction of metal compound to get free metal
   • Refining of metal.
2. Uses of common metals and non-metals :
   Uses of metals – for making machinery, automobiles, industrial gadgets, building, bridges, cooking utensils, electrical gadgets, jewellery, sheets.
   Uses of non-metals – oxygen is used by plants and animals for their survival, nitrogen is used by plants for their growth, chlorine is used in water purification to kill germs, sulphur is used for making sulphuric acid, tincture iodine has antiseptic properties.
3. Noble metals – Gold, silver and platinum are noble metals. They occur free in nature . and maintain their lustre for a long time. Platinum, gold and silver are used for making jewellery as they do not tarnish.

Question 5.
Purity of gold is 15 carat. What is the percentage’of gold in the ornaments ?
Answer:
24 carat purity of gold =100
∴ 1 carat purity or gold = 100/24
15 carat purity of gold = (100*15)/24 = 62.5 %

Question 6.
Give two uses of sulphur in chemical industry.
Answer:

• It is used in the manufacture of sulphuric acid.
• It is used in the manufacture of carbon disulphide, which is used as an industrial solvent.

Question 7.
How is sulphur useful in agriculture ? How is sulphur useful in medicine ?
Answer:
Sulphur powder is an excellent insecticide and fungicide. It is used in spraying fruit trees.

• Sulphur is the main constituent of skin ointments.
• Metallic sulphides of sulphur are used in the preparation of Ayurvedic medicines.

Question 8.
Give two important uses of silver.
Answer:

• It is used for making coins.
• Silver salts (silver bromide and silver iodide) are used for making photographic films.

Question 9.
Give two uses of gold.
Answer:

• Gold is used for making ornaments.
• Gold foils are used in the preparation of Ayurvedic medicines.

Question 10.
Give two uses of platinum.
Answer:

• It is used as a catalyst in the manufacture of sulphuric and nitric acid.
• Platinum catalytic converters use platinum as catalytic agent.

Question 11.
Which of the following will form acidic oxide and why :
P, K, Na, Ca?
Answer:
P (Phosphorus) will form acidic oxide because it is a non-metal.

Question 12.
You are given two materials X and Y. On hammering X is flattened, but Y breaks. Which one is a metal ?
Answer:
X is a metal because it flattens, i.e., it is malleable.

Question 13.
There are four materials A, B, C and D. A and D are hard and shiny, but B and C are dull and not very hard. Identify the metals and non-metals from A, B, C and D.
Answer:
A and D are metals.
B and C are non-metals.

Question 14.
Gaurav knows that wires can be made from copper and aluminium. He tries to make wire . from sulphur and carbon. Will he succeed ? Give reason also.
Answer:
No, he will not succeed because sulphur and carbon are non-metals. Non-metals are not ductile, that is, they cannot be drawn into wires.

3 Marks

Question 1.

1. Identify the most reactive and least reactive metal amongst the followings :
   Al, K, Cu, Au.
2. An iron knife kept dipped in blue copper sulphate solution changes to light green. Why ? Write the equation also. [KVS 2005]

Answer:

1. Most reactive metal is K and least reactive metal is Au.
2. An iron knife kept dipped in blue copper sulphate solution changes to light green because iron replaces copper from copper sulphate and forms iron sulphate. This happens because iron is more reactive than copper.
   Fe + CuSO₄ ——> FeSO₄ + Cu

Question 2.
Give reasons, why :

1. Silver is used in jewellery.
2. Copper is used in electrical wiring.
3. Sodium is stored in kerosene oil.

Answer:

1. Silver does not corrode and it is malleable and ductile, therefore, it can be used in jewellery.
2. Copper is used in electrical wiring because it is a good conductor of electricity.
3. Sodium has low ignition temperature. It oxidises quickly and bums when exposed to air. It can only be stored in a liquid hydrocarbon like mineral oil or kerosene oil.

Question 3.
Taking the examples of magnesium and sulphur explain how metals and non-metals produce oxides with different characteristics.
Answer:
Magnesium bums in oxygen to form magnesium oxide, which dissolves in water to form magnesium hydroxide – an alkali.
2Mg + O₂ ——-> 2MgO
MgO + H₂O ——-> Mg(OH)₂
Magnesium hydroxide changes red litmus into blue.
Sulphur bums in air to form sulphur dioxide, which dissolves in water to form sulphurous acid – an acid which turns blue litmus into red.
S + O₂ ——> SO₂
SO₂ + H₂O ——–> H₂SO₃

Question 4.
Compare the following chemical properties of metals and non-metals.

1. Formation of ions
2. Action with dilute acids
3. Action with hydrogen.

Answer:

1. Formation of ions.
   Metals form cations whereas non-metals form anions.
2. Action with dilute acids.
   Metals react with dilute mineral acid to liberate hydrogen.
   Non-metals do not react with dilute mineral acids.
3. Action with hydrogen.
   Metals do not react with hydrogen but non-metals react with hydrogen to form hydrides.

5 Marks

Question 1.
What happens when [KVS 2008]
(a) Hydrochloric acid is poured on aluminium foils ?
(b) Sodium is placed in water ?
(c) Sulphur dioxide is dissolved in water ?
(Write the chemical equation of the reaction involved)
Answer:

Question 2.

1. A copper spoon had fallen into a container containing dil.HCl. What would happen to it in three days time ? [DAV2008]
2. Give reasons for the following :
   • Metals are used for making bells.
   • We can’t use pure gold to make jewellery.
3. A metal ribbon bums in air with bright white light and forms a white powder.
   • Which metal is this ?
   • Give the equation of the reaction taking place.
   • The metallic oxide formed would be acidic or basic in nature ?

Answer:

1. Nothing will happen as copper does not react with hydrochloric acid.
2. • Metals have the property of sonorosity so they are used for making bells.
   • Pure gold cannot be used for making jewellery because it is very soft.
3. • Magnesium.
   • 2Mg + O₂ ——> 2MgO
   • Basic in nature.

Question 3.
Give reasons for the following : [KVS 2007]

1. Silver is used in making mirrors.
2. Aluminium is used to make electrical wire.
3. Iron is used in construction of bridges and houses.
4. Graphite is used as an electrode in the dry cell.
5. Iron sheets are galvanised before use.

Answer:

1. Silver has the ability to reflect light, therefore, it is used for making mirrors.
2. Aluminium is a good conductor of electricity, so, it is used for making electrical wires.
3. Iron is a strong metal, therefore, it is mixed with concrete to make bridges and houses.
4. Graphite is a good conductor of electricity, therefore, it is used as an electrode in dry cell.
5. Iron sheets are galvanised before use so that they do not corrode.

Question 4.
Which of the following statements is correct ? [NCERT]

• All metals are ductile.
• All non-metals are ductile.
• Generally, metals are ductile.
• Some non-metals are ductile.

Answer:
Generally, metals are ductile.

Question 5.
Fill in the blanks : [NCERT]

1. Phosphoms is a very ………… non-metal.
2. Metals are …….. conductors of heat and ………
3. Iron is ……… reactive than copper.
4. Metals react with acids to produce ………. gas.

Answer:

1. reactive
2. good, electricity
3. more
4. hydrogen.

Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false. [NCERT]

1. Generally, non-metals react with acids. ( )
2. Sodium is a very reactive metal. ( )
3. Copper displaces zinc from zinc sulphate solution. ( )
4. Coal can be drawn into wires. ( )

Answer:

1. F
2. T
3. F
4. F

Question 7.
Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties. [NCERT]

Answer:

Question 8.
Give reasons for the following : [NCT 2010]

1. Aluminium foils are used to wrap food items.
2. Immersion rods for heating liquids are made up of metallic substances.
3. Copper cannot displace zinc from its salt solution.
4. Sodium and potassium are stored in kerosene.

Answer:

1. Aluminium is a highly malleable metal and can be made into foils. So, it can be used to wrap food items.
2. Metals are good conductors of electricity, therefore, they are used for making immersion rods.
3. Copper is less reactive than zinc. Therefore, it cannot displace zinc from its salt solution.
4. Sodium and potassium are highly reactive metals. On exposure to air, they get oxidized. To avoid this they are stored in kerosene.

Question 9.
Match the substances given in Column I with their uses given in Column II. [NCERT]

Answer:

 Question 10.
What happens when [NCERT]

1. Dilute sulphuric acid is poured on copper plate ?
2. Iron nails are placed in copper sulphate solution ? Write word equations of the reactions involved.

Answer:

1. When sulphuric acid is poured on copper plate, copper sulphate and hydrogen gas are produced.
   Copper + Sulphuric acid ——-> Copper sulphate + Hydrogen (gas).
2. When iron nails are placed in copper sulphate solution, iron sulphate and copper are formed.
   Iron + Copper sulphate ——-> Iron sulphate + Copper

Question 11.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube. [NCERT]
(a) How will she find the nature of the gas ?
(b) Write down word equations of all the reactions taking place in this process.
Answer:
(a) The nature of gas can be found by passing it lime water, which will turn milky.

Question 12.
List different uses of metals that you come across in everyday life.
Answer:
Metals are used for making

• machinery
• automobiles, aeroplanes, trains, etc.
• pins, cooking utensils, electrical gadgets.
• electrical wires.
• thin sheets used for wrapping of food items, medicines, etc.

Question 13.
Choose appropriate words from the brackets and complete the statements.

1. Noble gases are found in (free state/compound forms).
2. Non-metals are generally (malleable/brittle).
3. Potassium after combustion will form (acidic oxide/basic oxide).
4. (Iodine/bromine) has antiseptic properties.
5. German silver has (copper/silver) as major constituent.

Answer:

1. Free state
2. Brittle
3. Basic oxide
4. Iodine
5. Copper

Question 14.
State whether the following statements are True or False :

1. Sodium is more reactive than magnesium.
2. Magnesium reacts with cold water.
3. All metals exist in solid form at room temperature.
4. Gallium has a low melting point.
5. Gold is alloyed with copper to make it hard.

Answer:

1. False
2. True
3. True
4. False
5. True

Question 15.
From among the set of metals — sodium, zinc, iron, copper, silver, select the following giving equations for each reaction :
(a) Two metals which will liberate hydrogen from water.
(b) One metal which is used to prepare hydrogen gas in the laboratory.
(c) One metal which will displace copper from copper sulphate solution.
(d) One metal which will not displace copper from copper sulphate solution.
Answer:

Question 16.
Name one metal which will fit each of the following description. Also write the equation of the reaction.
(a) A metal which floats on water, reacts with it and forms an alkali.
(b) A metal that displaces silver from silver nitrate solution.
(c) A metal which is used for galvanising iron.
(d) A metal that reacts with oxygen without burning.
(e) A metal that bums in oxygen with a bright light.
Answer:

Question 17.
A set of metals in order of their increasing chemical reactivity is given below : silver, copper, lead, iron, zinc, magnesium and sodium.

1. Which of the above metals is stored in kerosene ?
2. Which metals will react with cold water ?
3. Which gas will be liberated when metals react with cold water ?
4. Which of the metals will react with oxygen when heated ?
5. Which of the metals become black in the presence of hydrogen sulphide ?

Answer:

1. Sodium
2. Sodium
3. Hydrogen
4. Zinc, magnesium
5. Silver

Multiple Choice Questions

Question 1.
Which of the following properties is generally not shown by metals?
(a) Ductility
(b) Sonorous
(c) Dullness
(d) Electrical conduction
Answer:
(c)

Question 2.
The most abundant element in the universe is
(a) hydrogen
(b) oxygen
(c) helium
(d) carbon
Answer:
(a)

Question 3.
The ability of metals to be drawn into wires is known as
(a) ductility
(b) conductivity
(c) malleability
(d) sonorousity
Answer:
(a)

Question 4.
The most abundant element in the earth crust is
(a) iron
(b) oxygen
(c) silicon
(d) aluminium
Answer:
(b)

Question 5.
Galvanisation is a method qf protecting iron from rusting by coating with a thin layer of
(a) silver
(b) galium
(c) zinc
(d) aluminium
Answer:
(c)

Question 6.
The most abundant ihetal in earth crust is
(a) Cu
(b) Al
(c) Fe
(d) Zn
Answer:
(b)

Question 7.
An alloy is
(a) a compound
(b) a heterogeneous mixture
(c) a homogeneous mixture
(d) an element
Answer:
(c)

Question 8.
In extraction of copper, the flux used is
(a) FeO
(b) Si02
(c) CaO
(d) FeSi03
Answer:
(b)

Question 9.
Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following aljoys contain non-metal as one of its constituents?
(a) Amalgam
(b) Brass
(c) Bronze
(d) Steel
Answer:
(d)

Question 10.
Which of the following is purest form of carbon?
(a) Diamond
(b) Graph’ite
(c) Fullerenes
(d) Charcoal
Answer:
(c)

Question 11.
Which among the following alloys contain mercury as one of its constituents?
(a) Alnico
(b) Solder
(c) Stainless steel
(d) Zinc Amalgam
Answer:
(d)

Question 12.
Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying paint
(b) Applying grease
(c) Applying a coating of zinc
(d) all of these
Answer:
(c)

Question 13.
Generally, non-metals are not conductors of electricity, which of the following is a good conductor of electricity?
(a) Fullerenes
(b) Graphite
(c) Diamond
(d) Sulphur
Answer:
(b)

Question 14.
Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin
(b) zinc is less reactive than tin
(c) zinc is more reactive than tin
(d) zinc has a higher melting point than tin
Answer:
(a)

Question 15.
Electrical wires have a coating of an insulating materials. The material, generally used is
(a) sulphur
(b) graphite
(c) PVC
(d) none of these
Answer:
(c)

Question 16.
Which of the following non-metals is a liquid?
(a) Sulphur
(b) Phosphorus
(c) Carbon
(d) Bromine
Answer:
(d)

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