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NCERT Solutions for class 8 Science Materials: metals and non metals

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Exercise

Q1: Which of the following can be beaten into thin sheets?

Ans: (a) Zinc

Q2: which of the following statement is correct?

Ans:

Q3: Fill in the blanks

  1. Phosphorous is a very reactive non-metal.
  2. Metals are good conductors of heat and electricity.
  3. Iron is more reactive than copper.
  4. Metals react with acids to produce hydrogen gas.

Q4: Mark ‘T’ if the statement is true and ‘F’ if it is false.

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

Q5: Some properties are listed in the following Table. Distinguish between metal and non-metals on the basis of these properties.

Ans:

Properties

Metals

Non-metals

Appearance

Shiny

Dull

Hardness

Hard

Soft

Malleability

Malleable

Not malleable

Ductility

Ductile

Not ductile

Heat conduction

Good conductor of heat

Bad conductor of heat

Conduction of electricity

Good conductor of electricity

Bad conductor of electricity

Q6: Give reasons for the following:

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

Ans:

  1. Aluminium foils are used to wrap food items because it does not react with the food item and keep it warm for longer time.
  2. Immersion rods for heating liquids are made up of metallic substance because metals are good conductor of heat that allow easy heating of water.
  3. Copper cannot displace zinc from its salt solution because zinc is more reactive than copper.
  4. Sodium and potassium are stored in kerosene because they reactive air.

Q7: Can you store lemon pickle in an aluminium utensil? Explain.

Ans: No, we cannot store lemon pickle in an aluminium utensil because lemon pickle contains acid and aluminium reacts with acid that can spoil the pickle.

Q8: Match the substances given in column A with their uses in column B

Ans:

Column A

Column B

Gold

Jewelry

Iron

Machinery

Aluminium

Wrapping food

Carbon

Fuel

Copper

Electric wire

Mercury

Thermometers

Q9: What happens when

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

Ans:

  1. No reaction will take place because dilute sulphuric acid does not react with copper plate.
  2. When iron nail is placed in a copper sulphate solution it will displace copper from its compound and forms iron sulphate solution.

Iron (Fe) + Copper sulphate (CuSO4) -> Iron sulphate (FeSO4) + copper (Cu)

Q10: Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.

  1. a.     How will she find the nature of the gas?
  2. b.     Write down word equations of all the reactions taking place in this process.

Ans:

  1. To find the nature of gas, Saloni first needs to mix water with gas collected in the test tube. Then using the blue and red litmus nature of gas can be found. The blue litmus will turn red which means that the gas is acidic in nature.
  2. Equation of charcoal reaction with oxygen to form carbon  dioxide

C + O2 -> CO2

Equation of carbon dioxide gas reacts with water to form carbonic acid

            CO2 + H20 -> H2CO3

Q11:  One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewelry to the goldsmith to polish. Next day when they brought the jewelry back, they found that there was a slight loss in the weight. Can you suggest a reason for the loss of its weight?

Ans:  Gold jewelry is polished by dipping it into the mixture of hydrochloric acid and nitric acid. This mixture dissolves the outer layer of gold and shiny inner layer appears which causes loss in weight of gold jewelry.

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