Question 14 Marks
Differentiate between an efflorescent, deliquescent $\&$ hygroscopic substance with suitable examples.
Answer
View full question & answer→Efflorescent substances:
$(i)$ Lose wholly or partially their water of crystallisation when exposed to air.
$(ii)$ Become powdery.
$(iii)$ Washing soda $\ce{CaCO_3 \cdot 10 H_2O}$, Gauber's salt $\ce{Na_2SO_4 \cdot 10 H_2O}$, epsom salt $\ce{MgSO_47H_2O}$
$\ce{Na_2CO \cdot 10H_2O \xrightarrow{\text { dry air }} Na_2CO_3 \cdot H_2O + 9 H_2O}$
$(iv)$ Crystalline when hydrated.
Deliquescent substances:
$(i)$ Absorb moisture from atmosphere, absorb water and dissolve in it forming a saturated solution.
$(ii)$ Deliquescence is maximized in dry conditions.
$(iii)\ce{ NaOH , KOH , CaCl _2, MgCl _2, FeCl _3}$ are the examples.
$(iv)$ They are crystalline water soluble.
$\ce{FeCl _3 \longrightarrow FeCl _3}$
Crystal changes to Solution
Hygroscopic substances:
$(i)$ They are amorphous solids or liquids.
$(ii)$ Absorb moisture from the air of atmosphere.
$(iii)$ Do not change their original state.
$\ce{CaO}($quick lime$)$, cone. $\ce{H_2 SO_4, P_2O_5}$ and silica gel are the examples.
$\underset{\text { Conc. }}{ \ce{H_2 SO_4}} \longrightarrow \underset{\text { Conc. }}{\ce{H_2SO_4}} \quad$ $($State not changed$)$
is used for drying gases in laboratory.
$(i)$ Lose wholly or partially their water of crystallisation when exposed to air.
$(ii)$ Become powdery.
$(iii)$ Washing soda $\ce{CaCO_3 \cdot 10 H_2O}$, Gauber's salt $\ce{Na_2SO_4 \cdot 10 H_2O}$, epsom salt $\ce{MgSO_47H_2O}$
$\ce{Na_2CO \cdot 10H_2O \xrightarrow{\text { dry air }} Na_2CO_3 \cdot H_2O + 9 H_2O}$
$(iv)$ Crystalline when hydrated.
Deliquescent substances:
$(i)$ Absorb moisture from atmosphere, absorb water and dissolve in it forming a saturated solution.
$(ii)$ Deliquescence is maximized in dry conditions.
$(iii)\ce{ NaOH , KOH , CaCl _2, MgCl _2, FeCl _3}$ are the examples.
$(iv)$ They are crystalline water soluble.
$\ce{FeCl _3 \longrightarrow FeCl _3}$
Crystal changes to Solution
Hygroscopic substances:
$(i)$ They are amorphous solids or liquids.
$(ii)$ Absorb moisture from the air of atmosphere.
$(iii)$ Do not change their original state.
$\ce{CaO}($quick lime$)$, cone. $\ce{H_2 SO_4, P_2O_5}$ and silica gel are the examples.
$\underset{\text { Conc. }}{ \ce{H_2 SO_4}} \longrightarrow \underset{\text { Conc. }}{\ce{H_2SO_4}} \quad$ $($State not changed$)$
is used for drying gases in laboratory.