Class 8 - Chemistry - Metals and Non metals

Question 1:

Which of the following can be beaten into thin sheets?

(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

Answer:

Correct Option: - (a) Zinc.

Zinc is a metal rest all are non-metals. Therefore Zinc can be beaten into sheets.

 

 

Question 2:

Which of the following statements is correct?

(a) All metals are ductile.

(b) All non-metals are ductile.

(c) Generally, metals are ductile.

(d) Some non-metals are ductile.

Answer:

Correct Option: - (c) Generally, metals are ductile.

Exception to this is Mercury which is a metal but a liquid at room temperature. So it cannot be drawn into wires.

Therefore it is non-ductile.

Therefore except (c) all other options are incorrect.

 

 

Question 3:

Fill in the blanks:

(a) Phosphorus is very ________non-metal.

(b) Metals are _____conductors of heat and ______.

(c) Iron is _______reactive than copper.

(d) Metals react with acids to produce _______ gas.

Answer:

(a) Phosphorus is very reactive non-metal.

(b) Metals are good conductors of heat and electricity.

(c) Iron is more reactive than copper.

(d) Metals react with acids to produce Hydrogen gas.

 

 

Question 4:

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

(a) Generally, non-metals react with acids. ( )

(b) Sodium is a very reactive metal. ( )

(c) Copper displaces zinc from zinc sulphate solution. ( )

(d) Coal can be drawn into wires. ( )

Answer:

(a) Generally, non-metals react with acids. (F)

Reason: - Generally, metals react with acids and give H2 gas.

(b) Sodium is a very reactive metal. (T)

Reason: - Sodium, Potassium etc. is a very reactive metal.

(c) Copper displaces zinc from zinc sulphate solution. (F)

Reason: - Because the reactivity of zinc is higher than copper.

So, copper cannot displace zinc from zinc sulphate solution.

(d) Coal can be drawn into wires. (F)

Reason: - As coal is a non-metal, so it is non-ductile.

 

 

Question 5:

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

Properties                              Metals                                         Non-metals

  1. Appearance
  2. Hardness
  3. Malleability
  4. Ductility
  5. Heat Conduction
  6. Conduction of Electricity

Answer:

Properties

Metals

Non-Metals

1.     Appearance

Lustrous

Dull

2.     Hardness

Hard

Soft

3.     Malleability

Malleable

Non-Malleable

4.     Ductility

Ductile

Non-Ductile

5.     Heat Conduction

Good Conductor of Heat

Poor Conductor of Heat

6.     Conduction of Electricity

Good Conductor of Electricity

Poor Conductor of Electricity

 

 

 

Question 6:

Give reasons for the following:

(a) Aluminium foils are used to wrap food items.

(b) Immersion rods for heating liquids are made up of metallic substances.

(c) Copper cannot displace zinc from its salt solution.

(d) Sodium and potassium are stored in kerosene.

Answer:

  • Aluminium foils are used to wrap food items because aluminium is highly malleable metal. It can be beaten into sheets to form thin wrapping sheets.
  • Moreover it does not react with food items.
  • Immersion rods are made up of metallic substances because metals are good conductors of heat.
  • So they can conduct heat through them to the liquids. As a result liquid gets heated up very quickly.
  • Copper cannot displace zinc from its salt solution because the reactivity of zinc is higher than copper.
  • Only a metal which is higher reactive can displace a metal of lower reactivity.

Cu + ZnSO4 à No reaction

  • Sodium and potassium are highly reactive metals. They can catch fire even when they come in contact with air.
  • So, they have to be kept in kerosene.

 

 

Question 7:

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

Answer:

Lemon pickle cannot be stored in aluminium utensils, as metals react with acids to liberate hydrogen gas.

The lemon pickle contains acids, which can react with aluminium (metal) to liberate hydrogen gas. This can lead to the spoiling of the pickle.

Question 8:

In the following Table some substances are given in Column I. In Column II some uses are given. Match the items in column I with those in Column II.

Column I                                         Column II

(i) Gold                                           (a) Thermometers

(ii) Iron                                           (b) Electric wire

(iii) Aluminium                             (c) Wrapping food

(iv) Carbon                                    (d) Jewellery

(v) Copper                                    (e) Machinery

(vi) Mercury                                  (f) Fuel

Answer:

             Column I

                Column II

(i)                Gold

      (d)  Jewellery

(ii)              Iron

(e)  Machinery

(iii)            Aluminium

      (c) Wrapping Food

(iv)            Carbon

(f)   Fuel

(v)              Copper

      (b) Electric wire

(vi)            Mercury

(a)  Thermometers

 

Question 9:

What happens when?

(a) Dilute sulphuric acid is poured on a copper plate?

(b) Iron nails are placed in copper sulphate solution?

Write word equations of the reactions involved.

Answer:

  • As copper does not react with dilute sulphuric acid.
  • Therefore, no reaction takes place when dilute sulphuric acid is poured on a copper plate.
  • But when concentrated sulphuric acid is poured over copper plate, effervescence is observed.
  • This happens because of formation of hydrogen gas.

Copper + Sulphuric acid  à Copper sulphate + Hydrogen gas

Cu + H2SO4 → CuSO4 + H2

  • Iron nails are placed in copper sulphate solution because the reactivity of iron is more than copper.
  • So, iron will displace copper from copper sulphate solution. The blue colour of copper sulphate fades away.

Iron + Copper sulphate à Iron sulphate + Copper

Fe + CuSO4 à FeSO4 + Cu

 

 

Question 10:

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

(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:

  • She should add some water in the test tube in which gas is collected. Shake the test tube. Bring near the test tube litmus paper.
  • The solution will change blue litmus to red.

This shows the gas is acidic.

  • Carbon from Charcoal + Oxygen à Carbon dioxide

C + O2 à CO2

Carbon dioxide + Water à Carbonic acid

CO2 + H2O à H2CO3

Carbon dioxide + lime water à Calcium Carbonate + Water

CO2 + Ca (OH) 2 à CaCO3 + H2O

 

 

Question 11:

One day Reeta went to a jeweller’s shop with her mother. Her mother gave 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?

Answer:

To polish a gold ornament, it is dipped in an acid (called Aqua Regia).

The outer layer of gold dissolves in the acid and the inner shiny layer are visible. As there is loss of upper layer of jewellery, therefore, its weight is reduced.

 

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