Page 276 - Physical chemistry understanding our chemical world

PROPERTIES OF LOWRY–BRØNSTED ACIDS AND BASES 243

stage in the battle, the German forces filled the air above the enemy trenches with
chlorine gas.
Elemental chlorine Cl 2 dissolves slightly in water, and hydrolyses
some of the water to yield hypochlorous acid, HOCl, according to Hypochlorous acid,
HOCl, is one of the
active components in
(6.15)
Cl 2(aq) + H 2 O (l) −−→ HCl (aq) + HOCl (aq)
household bleach.
The reaction in Equation (6.15) occurs readily in the lungs and
eyes (the sensitive tissues of which are lined with water) to cause
After this battle, both
irreparable damage. Troops exposed to chlorine apparently experi-
sides showed reluc-
enced a particularly slow and nasty death.
tance to employ poi-
The German troops did not advance, because they were not sure
sonous gases again,
if the gas masks issued to their own troops could withstand the beingafraidit would
chlorine. They were also deterred by the incursion of a Canadian drift back and poi-
regiment. But one of the young Canadian soldiers knew a little son their own troops.
chemistry: sniffing the gas, he guessed its identity correctly, and Cl 2 gas also caused
ordered the soldiers to cover their faces with handkerchiefs (or extensive corrosion
bandages) soaked in their own urine. The idea spread quickly, and of rifles and artillery
the Canadians, together with two Yorkshire territorial battalions, breech blocks, making
them unusable.
were able to push back the German troops.
One of the major constituents of urine is the di-amine, urea
(III). Each amine group in urea should remind us of ammonia in
Reminder:toa chem-
Equation (6.11). Solutions of urea in water are basic because the
ist, the word basic does
two amine moieties each abstract a proton from water, to generate
not mean ‘elementary’
an ammonium salt and a hydroxide ion:
or ‘fundamental’, but
‘proton abstracting’.
O

H 2 N NH 2
(III)

O O
+ 2H 2 O
H 2 N NH 2 H 3 N NH 3
2OH − (6.16)

−
The two OH ions formed during Equation (6.16) explain why aqueous solutions of
urea are alkaline.
As we saw above, chlorine forms hypochlorous acid, HOCl. The hydroxide ions
generated from urea react with the hypochlorous acid in a typical acid–base reaction,