Long Answer Question - Materials : Metals And Non-Metals Notes | EduRev

Science Class 8

Class 8 : Long Answer Question - Materials : Metals And Non-Metals Notes | EduRev

The document Long Answer Question - Materials : Metals And Non-Metals Notes | EduRev is a part of the Class 8 Course Science Class 8.
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Q1: Explain physical and chemical properties of metals and non-metals.  

Ans: Chemical properties of metals:

  1. Reaction with oxygen:-
    Metals react with oxygen to form metallic oxides. These are basic oxides because they react with water to form bases.
    Eg. Magnesium burns in air to form magnesium oxide.
    2 Mg + O2 → 2 MgO 
  2. Reaction with water:-
    Metals react with water to form metal hydroxides and hydrogen.
    Eg. Sodium reacts with water to form sodium hydroxide and hydrogen.
    2Na + 2H2O → 2NaOH + H2
    E.g. Magnesium reacts with water to form magnesium hydroxide and hydrogen.
    Mg + H2O → Mg(OH)2+ H2
  3. Reaction with acids:-
    Metals react with acids to form metallic salts and hydrogen.
    Eg. Zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen.
    Zn + 2HCl → ZnCl2+ H2
  4. Metals replace metals:-
    A more reactive metal replaces a less reactive metal from its salt solution.
    Eg. Magnesium replaces copper from copper sulphate solution to form magnesium sulphate and copper.
    Mg + CuSO4 → MgSO4+ Cu
    Zinc replaces copper from copper sulphate solution to for zinc sulphate and copper.
    Zn + CuSO4 → ZnSO4 + Cu

Chemical properties of non-metals:

1. Reaction with oxygen:

Non-metals react with oxygen to form non-metallic oxides. These oxides are acidic oxides because they react with water to form acids.

Eg. Sulphur burns in air to form sulphur dioxide. Sulphur dioxide reacts with water to form sulphurous acid.

S + O2 → SO2

SO2+ H2O → H2SO3

2. Reaction with water:
Non-metals do not react with water

3. Reaction with acids:
Most non-metals do not react with acids.
Some non-metals like sulphur react with concentrated nitric acid to form sulphur dioxide, nitrogen dioxide and water.
S + 4HNO3→ SO2 + 4NO2+ 2H2O

Physical properties of metals:

  • Metals are solid except mercury.
  • Metals are hard.
  • Metals are malleable that is can be beaten into thin sheets.
  • Metals are ductile that is can be drawn into wires.
  • Metals produce ringing sounds are called sonorous.
  • Metals are lustrous.
  • Metals are good conductors of heat and electricity.

Physical properties of non-metals:

  • Non- metals are solid, liquid or gas.
  • Non- metals which is solid are brittle (diamond is the hardest).
  • Non- metals are soft and dull in appearance.
  • Non- metals are not malleable, and break down into powdery mass on tapping with a hammer.
  • They are not sonorous.
  • They are poor conductors of heat and electricity..

Q2: Explain differences between metal and non-metal on the basis of their properties like hardness, malleability, ductility, appearance and heat conduction. 

Ans:

MetalsNon - metals
  • Metals have Metals are hard except sodium and potassium which are soft
  • Metals are malleable and can be beaten into thin sheets through heating and hammering
  • Metals are ductile and can be drawn into wires
  • Metals are good conductors of heat
  • Metals are good conductor of electricity
  • Non-Metals are generally soft except diamond which is very hard
  • Non-Metals are non-malleable, brittle and cannot be beaten into thin sheets through heating and hammering
  • Non-Metals are not ductile and cannot be drawn into wires
  • Non-Metals are poor conductors of heat
  • Non-Metals are poor conductor of electricity

Q3: Give reason why copper cannot displace zinc from its salt solution, and why sodium and potassium are stored in kerosene.

Ans: Copper cannot displace zinc from its salt solution: because Zinc is more reactive than copper. A more reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal. Therefor Copper cannot displace zinc from its salt solution.
Sodium and potassium are stored in kerosene because Sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. It is, therefore, stored in kerosene.
Q4: Write word equation of the following reactions:

  1. Sulphur burning in air
  2. Sulphur reacts with concentrated acid
  3. Iron nail placed in copper sulphate solution.

Ans: 

  1. Sulphur burning in air: Sulphur burns in air to form sulphur dioxide. Sulphur dioxide reacts with water to form sulphurous acid.
    S + O2→ SO2
    SO2+ H2O→ H2SO3
  2. Sulphur reacts with concentrated acid to form sulphur dioxide, nitrogen dioxide and water.
    S + 4HNO3 → SO2+ 4NO2+ 2H2O
  3. When Iron nail is placed in copper sulphate solution iron replaces copper from copper sulphate, thus nails becomes copper plated and blue colour of copper sulphate solution disappears and solutions turns from blue to light yellowish. Following reaction occurs:
    Copper sulphate (CuSO4) + Iron nail (Fe) → Iron sulphate (FeSO4) + Copper (Cu)

Q5: What happens when dilute sulphuric acid is poured on a copper plate?

Ans: When dilute sulphuric acid is poured in a copper plate then copper undergo reaction with acid to form metal salts CuSO4 a blue crystalline solid and hydrogen gas:
Cu (Copper) + H2SO4 (Sulphuric Acid) → CuSO4(Copper sulphate) + H2 (Hydrogen gas)

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