Everyday Life and Chemistry - Essentials of Chemical Education - page 229

8.2.13 Motoring: Example “Alcohol Test”

Alcohol test “ chromate type ” (E8.16): To check the blood alcohol content of drivers
in road traffic, the police use either detection tubes or test equipment on the basis of
infrared spectroscopy. The detection tubes are used to first estimate the alcohol
content in breathing air. These tubes contain yellow crystals of potassium chromate
mixed with sodium hydrogen sulfate. In the presence of a wet steam of alcohol, a
reduction to green-colored chromium(III)-compounds occurs, so the color changes
from yellow to green:

2CrO 4 2 ð 2H þ ð Cr 2 O 7 2 ð

aq ; yellow Þþ aq Þ! aq Þþ H 2 O ABR

Cr 2 O 7 2 ð 8H þ ð

3CH 3 CH 2 OH ð g Þþ aq Þþ aq Þ! 3CH 3 CHO ð aq Þ

2Cr 3 þ ð

þ Þþ

7H 2 O RR

green

8.2.14 Manufacturing: Example “Fertilizer”

In addition to natural fertilizers (dung, slurry), we have mineral fertilizers. On the
one hand, they are extracted from salt stocks under the Earth's surface: potassium-,
calcium- and magnesium salts, nitrates, phosphates, etc. On the other hand, nitrate
and ammonium salts are produced artificially from nitrogen in the air by the Haber
process:

N 2 ð g Þþ 3H 2 ð g Þ! 2NH 3 ð g Þ RR

2NH 3 (g) þ 3 1 = 2 O 2 (g Þ! 2NO 2 (g) þ 3H 2 O (g) RR

4NO 2 (g) þ 2H 2 O ð l Þþ O 2 (g) ! 4HNO 3 ð aq Þ RR

NH 3 ð aq Þþ HNO 3 ð aq Þ! NH 4 NO 3 ð aq Þ ABR

Insoluble calcium phosphate - from deposits in North Africa - is converted with
pure sulfuric acid to soluble dihydrogen phosphate, which is ready to be used in
fertilizing mixtures:

Ca 3 ð PO 4 Þ 2 (s)

þ

2H 2 SO 4 ð

Þ! þ ð

H 2 PO 4 Þ 2 (s) ABR

l 2CaSO 4 (s) Ca