(a) Why does common salt get wet during the rainy season ?
(b) How can this impurity be removed ?
(c) Name a substance which changes the blue colour of copper sulphate crystals to white.
(d) Name two crystalline substances which do not contain water of crystallisation.
(a) Why does common salt get wet during the rainy season ?
(b) How can this impurity be removed ?
(c) Name a substance which changes the blue colour of copper sulphate crystals to white.
(d) Name two crystalline substances which do not contain water of crystallisation.
(a) This means that salt is hygroscopic, so it absorbs both liquid water and water vapor present in air. Common salt is hygroscopic in nature. It absorbs moisture from the atmosphere which has high humidity in the rainy season.
Normally, the common salts found are impure NaCl containing impurities like CaSO4 , Na2SO4 , MgCl2 , CaCl2 etc., which are hygroscopic in nature and absorbs water from atmospheric moisture during the rainy season and so the salt gets wet. But pure NaCl would not get wet.
(b) Among various methods to increase the purity of common salt, the washing method is simple and was considered suitable to the factories in Japan, then we studied the effects of the washing method using saturated salt solution or brine, to increase the purity by the removal of impurities such as calcium or magnesium in the salt.
The following results were obtained.
(1) The magnesium is removed almost perfectly from the salt by the washing, but the calcium is removed 50-70% of total calcium.
(2) There are a proportinal relation between the magnesium contents of the washing liquid and the washed salt.
(3) The effect of the times of washing or the quantity of washing liquid is not great.
(4) The purity of the washing salt is increased on drying as comparable to the quality of “Refined Salt”
(c) Hydrated Copper Sulphate crystals [CuSO4.5H2O] are blue in colour.
When copper sulphate crystals are heated strongly, they loose all the water of crystallization and form anhydrous copper sulphate [which is white in colour].
CuSO4.5H2O ---------> CuSO4 + 5H2O
Hydrated Anhydrous
Copper sulphate Copper sulphate
The colour in the substance is given by this water of crystallisation only. So when we heat it, the water molecules escape into surroundings and a white coloured anhydrous copper sulphate is left behind and when you heat it it looses the water of crystallisation hence turns white.
(d) KCl and NaCl
(a) This means that salt is hygroscopic, so it absorbs both liquid water and water vapor present in air. Common salt is hygroscopic in nature. It absorbs moisture from the atmosphere which has high humidity in the rainy season.
Normally, the common salts found are impure NaCl containing impurities like CaSO4 , Na2SO4 , MgCl2 , CaCl2 etc., which are hygroscopic in nature and absorbs water from atmospheric moisture during the rainy season and so the salt gets wet. But pure NaCl would not get wet.
(b) Among various methods to increase the purity of common salt, the washing method is simple and was considered suitable to the factories in Japan, then we studied the effects of the washing method using saturated salt solution or brine, to increase the purity by the removal of impurities such as calcium or magnesium in the salt.
The following results were obtained.
(1) The magnesium is removed almost perfectly from the salt by the washing, but the calcium is removed 50-70% of total calcium.
(2) There are a proportinal relation between the magnesium contents of the washing liquid and the washed salt.
(3) The effect of the times of washing or the quantity of washing liquid is not great.
(4) The purity of the washing salt is increased on drying as comparable to the quality of “Refined Salt”
(c) Hydrated Copper Sulphate crystals [CuSO4.5H2O] are blue in colour.
When copper sulphate crystals are heated strongly, they loose all the water of crystallization and form anhydrous copper sulphate [which is white in colour].
CuSO4.5H2O ---------> CuSO4 + 5H2O
Hydrated Anhydrous
Copper sulphate Copper sulphate
The colour in the substance is given by this water of crystallisation only. So when we heat it, the water molecules escape into surroundings and a white coloured anhydrous copper sulphate is left behind and when you heat it it looses the water of crystallisation hence turns white.
(d) KCl and NaCl
