HSEB notes | Sulphuric acid as a dehydrating agent, an oxidant and an acid

i. Sulphuric acid as a dehydrating agent :

H2SO4 has a great affinity for water, with water it forms a hydrate with evolution of high heat.

H2SO4 + H2O ----------> H2SO4 + H2O + Heat

Example showing sulphuric acid as a strong dehydrating agent are as follows :

1. Charring of sugar : It removes water molecule from sugar or sucrose and chars it with production of black carbon mass.

C12H22O11 + H2SO4 ---------- > 12 C (black mass)  + 11 H2O

2. It remove water of crystallization from blue cuppor sulphate crystals and turn it into white.
CuSO4 . 10 H2O (blue)+ H2SO4 ---------- > CuSO4 . H2O (white) + H2SO4. 4 H2O

3. It remove water from oxalic , formic acid and etyl alchohol :

With formic acid :

HCOOH + H2SO4 ---------- > CO + H2O

With oxalic acid :

(COOH)2 + H2SO4 ---------- > CO + CO2 + H2O

With ethyl alchohol :

C2H5OH + H2SO4 ---------- > C2H4 + H2O

ii. H2SO4 as an oxidizing agent :

1. With non-metals : Hot and conc H2SO4 can oxidize non-metals like carbon, sulphur and phosphorous.

With carbon :
H2SO4 ---------- > SO2 + H2O + [ O ]
C + [ O ] ------------ > CO2

With phosphorous :

P4 + 10 H2SO4 ----------- > 4 H3PO4 + 10 SO2 + 4 H2O

With sulphur 
:
S + H2SO4 ----------- > SO2 + H2O

2. With bromides and iodides : Conc and hot H2SO4 can oxidize bromides (HBR , KBR) and iodides (KI, HI) to free bromine and iodine respectively.

HBR - H2SO4 ----------- > SO2 + H2O + BR2
HI + H2SO4 ------------ > SO2 + H2O + I2

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