Question

(a) Why is crystallisation technique better than evaporation technique?

(b) Write any two physical properties of each metals and nonmetals.

Answer 1

(a) Different separation techniques are present depending upon the property of the substance to be separated, crystallisation and evaporation are two among them.

Crystallisation technique

• This method involves the separation of a solid substance from the solution by cooling it.
• It also used to purify the solid substance present in the solution.
• To separate copper sulphate crystals from the solution we can take this method.
• First of all heat the solution of copper sulphate in water, so that water evaporates off.
• When the solution become concentrated remove the china dish from the heating setup and allowed it to cool.
• Crystals of copper sulphate will be formed and we can decant the water layer.
• Transfer the crystals of copper sulphate and press them with a filter paper.

Evaporation technique

• It is used to separate the solid substance from the solution by evaporating off the solvent part in it.
• When the solute-containing solvent is heated gently, the solvent part will evaporate and solid solute will be obtained.

Crystallisation technique is better than evaporation because,

• Some solids like sugar will charred or deomposed when heated.
• To obtain crystals of the solid, crystallisation is best where evaporation doesn't give the crystals.
• The impurities which are soluble in nature can not be removed by evaporation technique.

Therefore, crystallisation technique is better than the evaporation technique

(b) Substances are classified into metals and nonmetals depending upon the properties

Metals	Nonmetals
Sustances which are generally hard, but exceptions are there sodium and potassium which are soft.	Nonmetals are generally soft but diamond is an exception which is the hardest natural substance.
Metals are good conductors of heat and electricity	Nonmetals are bad conductors of heat and electricity but graphite is an exception which is a good conductor of electricity
Example: Silver, Gold	Example: Sulphur, Oxygen