Page 266 - Chemistry ICSE Class X

252 ICSE Chemistry – 10
Physical and Chemical Properties of Sulphuric Acid
^ƵůƉŚƵƌŝĐ ĂĐŝĚ ŝƐ ƵƐĞĚ ŝŶ ƚǁŽ ĨŽƌŵƐ͗
ͻഩ ŽŶĐĞŶƚƌĂƚĞĚ ƐƵůƉŚƵƌŝĐ ĂĐŝĚ ;ĐŽŶĐ͘ What are the physical properties of concentrated
H ^K Ϳ
2
ϰ
ͻഩ ŝůƵƚĞ ƐƵůƉŚƵƌŝĐ ĂĐŝĚ ;Ěŝů͘ , ^K Ϳ sulphuric acid
2 ϰ
Concentrated sulphuric acid is a colourless, viscous, heavy liquid (density
1.84 g/mL at 298 K). It contains 98% H SO and 2% water. So, concentrated
dŚĞ ĚŝƐƐŽůƵƟŽŶ ŽĨ ĐŽŶĐĞŶƚƌĂƚĞĚ 2 4
ƐƵůƉŚƵƌŝĐ ĂĐŝĚ ŝŶ ǁĂƚĞƌ ŝƐ Ă ŚŝŐŚůLJ sulphuric acid is written as H SO (l).
2
4
ĞdžŽƚŚĞƌŵŝĐ ƌĞĂĐƟŽŶ͘ ƒ It fumes in moist air.
ƒ Sulphuric acid boils at 338°C.
ƒ Pure sulphuric acid is a poor conductor of electricity. However, when
dissolved in water, it gives a conducting solution.
ƒ Concentrated sulphuric acid is highly corrosive and chars the skin or
any cellulosic material.
ƒ It dissolves in water with the evolution of heat.
What are the chemical properties of conc. sulphuric acid

Some typical reactions of conc. H SO are described below:
4
2
ƒ #HſPKV[ HQT YCVGT %QPEGPVTCVGF UWNRJWTKE CEKF JCU UVTQPI CHſPKV[
for water. That is, EQPEGPVTCVGF UWNRJWTKE CEKF KU C RQYGTHWN
dehydrating agent.
Concentrated sulphuric acid can remove water from substances like
sugar, paper, wood, copper sulphate crystals and skin.
Activity: Take about 2-3 g of powdered sugar (canesugar or sucrose) in
a test tube. Add a few drops of concentrated H SO over it. Observe it.
4
2
After sometime, the sugar in the test tube turns black. This is called
charring of sugar.
Charring of sugar is due to its dehydration by concentrated sulphuric
acid.
C H O (s) + H SO o 12C(s) + H SO .11H O
22
2
11
12
2
2
4
4
Fig. 11.2 Sulphuric acid as a sugar conc. sulphuric carbon
dehydrating agent acid (black)
Š Concentrated H SO can also dehydrate copper sulphate crystals
2
4
(CuSO .5H O)
2
4
Activity: When a drop of concentrated sulphuric acid is placed
over powdered copper sulphate crystals (blue), it turns white. This
is due to the removal of water of crystallisation from the copper
sulphate crystals.
CuSO .5H O(s) + H SO o CuSO (s) + H SO .5H O
2
2
4
2
4
4
2
4
copper sulphate conc. copper sulphate
crystals (blue) sulphuric acid anhydrous (white)
Š Concentrated sulphuric acid causes burns on skin. This is also due
to the dehydration of skin by conc. H SO .
2
4
ƒ Oxidising property. Hot concentrated sulphuric acid acts as an
oxidising agent.
Š It oxidises carbon to carbon dioxide.
'
2H SO (l) + C(s) o 2SO (g) + 2H O(l) + CO (g)
2
4
2
2
2
Š It oxidises sulphur to sulphur dioxide.
2H SO (l) + S(s) o 2H O(g) + 3SO (g)
2
2
4
2
conc. sulphur sulphur dioxide