Chemistry Reference
In-Depth Information
For example, concentrated sulfuric acid is used:
•
for making detergents (Chapter 15, p. 239)
•
as a catalyst (Chapter 7, p. 109 and Chapter 14,
p. 224)
•
as a dehydrating agent (see p. 202 for the effect
it has on hydrates such as copper(ii)
ii
) sulfate
pentahydrate).
However, the concentrated acid is often mixed with
water to form dilute sulfuric acid. The diluted acid
is used:
hydrogen
dilute
sulfuric
acid
zinc granules
water
•
for making fertilisers (Chapter 11, p. 180)
•
for treating metals to remove oxidation
('pickling') before painting
•
in anodising aluminium (Chapter 5, p. 76)
•
as the acid in car batteries
•
for making paints, dyes and fibres
•
as a common laboratory reagent.
Figure 12.8
The laboratory preparation of hydrogen gas.
The preparation of the acid salt with sodium hydroxide
requires twice the volume of acid as that used in the
preparation of the normal salt. Therefore, if 25 cm
3
of
dilute sulfuric acid were required to form the normal
salt from a given volume of alkali of a particular
concentration then 50 cm
3
of the same acid solution
would be required to produce the acid salt, sodium
hydrogensulfate, from the same volume of alkali.
sodium
hydroxide
NaOH(
aq
)
Properties of sulfuric acid
Dilute sulfuric acid
Dilute sulfuric acid is a typical strong
dibasic
acid.
A dibasic acid is one with two replaceable hydrogen
atoms which may produce two series of salts -
normal and acid salts (Chapter 8, pp. 122 and 126).
It will react with bases such as sodium hydroxide
and copper(
ii
) oxide to produce normal salts, called
sulfates
, and water.
•
With sodium hydroxide:
sodium
hydroxide
2NaOH(
aq
)
+
+
sulfuric
acid
H
2
SO
4
(
aq
)
sodium
hydrogensulfate
NaHSO
4
(
aq
)
+
+
water
H
2
O(
l
)
→
●
●
→
Sulfates
The salts of sulfuric acid, sulfates, can be identified
by a simple test-tube reaction. To test for a sulfate,
add a few drops of dilute hydrochloric acid to your
unknown followed by a few drops of barium chloride.
If a sulfate is present, a white precipitate of barium
sulfate forms.
barium ions
Ba
2+
(
aq
)
+
sulfuric
acid
H
2
SO
4
(
aq
)
sodium
sulfate
Na
2
SO
4
(
aq
)
+
water
H
2
O(
l
)
→
●
●
→
+
+
+
+
sulfate ions
SO
4
2−
(
aq
)
barium sulfate
BaSO
4
(
s
)
→
→
•
With copper(ii)
ii
) oxide:
copper(
ii
)
oxide
CuO(
s
)
+
+
sulfuric
acid
H
2
SO
4
(
aq
)
copper(
ii
)
sulfate
CuSO
4
(
aq
)
+
water
H
2
O(
l
)
→
●
●
→
Many sulfates have very important uses, as can be
seen from Table 12.1.
Table 12.1
Uses of some metal sulfates.
+
It also reacts with carbonates to give normal
salts, carbon dioxide and water, and with reactive
metals to give a normal salt and hydrogen gas. The
reaction between zinc and sulfuric acid is often
used to prepare hydrogen gas in the laboratory
(Figure 12.8).
Salt
Formula
Use
Ammonium
sulfate
(NH
4
)
2
SO
4
Fertiliser
Barium
sulfate
BaSO
4
'Barium meal' used in diagnostic
medical X-ray studies
CaSO
4
.
2
H
2
O
Calcium
sulfate
'Plaster of Paris' used to set bones
zinc
Zn(
s
)
+
+
sulfuric acid
H
2
SO
4
(
aq
)
zinc sulfate
ZnSO
4
(
aq
)
+
+
hydrogen
H
2
(
g
)
→
→
Magnesium
sulfate
MgSO
4
In medicine it is used as a laxative
