Win
stuff
em
InfoCh
fe
r li
Water fo
ists
and chem
chemistry r
tigates the
wate
gate inves to access clean
le
Tom West
more peop
helping
Magnificent molecules
Phillip Broadwith highlights one of his favourite molecules.
In this issue: silver nitrate
| JUNE 2011
ISSUE 129
issue
In this
Glutamate delicious
of
The source
sensations
savoury
Castle
The Last cannon fire a
a water
Can
chain?
hook and
chemistry
Backyard of Space Dust
The science
the life
A day in rt MP
Huppe
Julian
Plus ...
s
Prize puzzle
ANDREA
SCHAFER
chemistry
careers
chemnet
events
cutting-edg
e chemistry
chemistry
on the web
Editor
ding on the
Karen Ogilvie
h
rocks). Depen
issue 58
t editor
in soil and may have been throug s,
Assistan
july 2011
underground
David Sait
solid particle
glass of water
to life
source, your tion steps to remove al pollutants,
Layout
ance of water , makes
n
up the import
Scott Ollingto
several purifica ls and ions, chemic to drink.
s surface
you sum
r
minera
of the planet’ adults need to
is safe
How can
Publishe
-Seijo
dissolved
before it
and
covers 70%
Campos
It
one
viruses
body,
Bibiana
is often to
than
and
on Earth?
human
first step
bacteria
ent to
But still more cannot
70% of the
plant, the
(0.1 µm or
is a supplem
is
every day.
up 50 to
es,
InfoChem Chemistry and
purification
2.5 litres
microscopic
ping countri
n in
At a water
water which
g,
removing
a year by
Educatio
the
by
drink around , mostly in develo
in
washin
water
d six times Chemistry,
ded
a
cooking,
publishe
of
clarify the
of dirt suspen particles carry
Society
billion people
drinking,
ing to UK
the Royal
particles
House,
water for
ck, accord
which
. The dirt
Graham
smaller)
access safe or rearing livesto
Thomas
surface,
or cloudy
in eight people
their
one
murky
ge,
on
it
ded
crops
Cambrid
charge
make
suspen
Meanwhile pollutants,
growing
electrostatic other and remain
s
al Action.
CB4 0WF.
er. To
negative
ill,
that contain
charity Practic
01223 420066 .org
repel each
of a contain
make them
drink water
means they
likely to
email: eic@rsc chem
at the bottom
flocculants
So how can
in the world
that are
.org/info
www.rsc
or viruses
charity Water. anywhere in instead of settling s, chemicals called
ry,
bacteria
ed group
contain soluble s,
particle
of Chemist Hello
to drink,
to US-bas
Flocculants
particle
Society
remove the
water safe
and welcom
according
© The Royal1752-0533
to the water. negatively-charged stick
e to
help to make
July issue
the
are added
2011. ISSN:
chemistry
of ChemN the
g them to
, which attract
et
News.
which
and allowin
the world?
has cationslising their charge
clumps (flocs)
comes out
and larger
neutra
Exploding
water that
to form larger
watermelons
Safe supply on the tap, the
accumulating
together
killer salad
and
turn
as rain and
–
When you
since falling (water contained
on with food what is going
way
207890
at the
come a long or in groundwater
Number momen
d Charity
ir
t?
Registere
in a reservo
In this issue
we take a
at agricul
tural chemis look
1 14:59:21
Agricul
25/05/201
tural chemis try.
A rapidly
try
aims at preserv
often
expanding
ing and
world popula
affluence
increasing
in the
the
water availab developing world tion, increasing
soil, mainta fertility of
ining and
significantly ility mean that we and limited land and
To cope with
improving
have
the agricul
productivity and sustainably increas no alternative
simple accuratextremes of water
yield, and
tural
quality and
improving
to provide
e agricultural but to
e water
Thendd
targeted
1
the
quality of
World
water deliver monitoring devices availability
Bank estima food, animal feed
the crop.
E_Water.i
- FEATUR
and fuel.
to increas
and
y system
tes that cereal
0411INFO
e by 50%
s are needed
Developments
These issues
production
and meat
between
.
needs
production
2000 and
improvements in genetic modific
important are more
2030
by
including
than ever,
ation offer
those of develo to meet the growin 80%
disease resistanfor agriculture,
as food
demand
many
such
efficiency
is outstrip
can be influen ping nations. Agriculg demands
ping
grow in nutrien ce and crops that as creating better
supply. Innova
improved
tural
are design
t poor soil.
tions in
pest control ced in many ways
chemicals
ed to
science of
including
, a better
Scientists
and
unders
plant
need to develo
become critical farming will
management. growth and improv tanding of the
and high
in the
protein/high p new vaccine
future,
ed water
so we
s, medicin
also need
calorie feeds
to improv
look at what also take a
for livestoc es
How can
e
genetics
k. They
the chem
in selectiv our understanding
the career is involved in
e breedin
the role of
ical scien
new hybrids
of an agricul
Chemistry
g and the
chemist.
ces help?
.
tural
is
engineering
pesticides key to developing
of
Sensors and
more targete
in
processing
against pests order to deliver the
d
to minimi
tools need
maximum
se any loss
to be develo
environment. with minimum effects
potency
of
that may
ped
on the
occur through quality and value
to produc
crop handlin
g and storage ts
.
Agricultura
l productivity
Welcome
to issue 58
fochem
.rsc.org/in
www
By 2030,
the
than 20% world’s population
to over eigh
will have
increased
t billion!
by more
Stephanie
Fernandes
– Editor
Chemnet
- July 2011.indd
1
www.rsc.o
rg/chemn
Registere
et
d Charity
Number
207890
21/06/201
In the late 19th century, anyone
wanting to pursue the latest
photographic craze had to be
able to handle a bewildering array
of chemicals to prepare, fix and
develop photographic plates.
Often, each photographer would
mix their solutions to a unique
recipe, tweaked as their experience
grew. Whatever the recipe, what
was needed was a chemical that
changed colour on exposure to light.
1 12:38:13
Win £25 of
Amazon
vouchers
RSC Student Magazine...
Boring title, isn’t it?
InfoChem and ChemNet News
are merging to form a new,
bigger, exciting student
magazine.
We need your help to find a
title. Choose a name from this
list – or perhaps you have a
better suggestion?
Firework
ChemZone
Alchemy
Explosion
Indicator
Elements
Tell us your choice at:
http://svy.mk/p4vy6W
by 7 October 2011.
We’ll select one entry at
random to receive a
£25 Amazon voucher.
Chemical acrostic
no.20 winner
The winner was Lucy Browne
from St George’s School for
Girls, Edinburgh, who correctly
identified the metal ore as
haematite.
4
Silver halide salts are ideal – when
illuminated they rapidly turn black
as they decompose to silver metal.
The problem from a photographer’s point of view is
that they are insoluble, so they’re difficult to apply in
thin films to photographic plates; and too sensitive,
so can’t be stored easily for a long time. The answer?
Silver nitrate, AgNO3.
Silver nitrate itself is not light-sensitive enough
to be used directly in photography, but this is an
advantage when it comes to storage. However, it
is soluble and easily displaces other metals from
their salts, so the sensitive silver halides could be
produced just before being popped into the camera.
In the earlier ‘wet plate’ processes, solutions of
salts like potassium bromide were applied to glass
plates, which would then be dunked into a silver
nitrate bath to displace the potassium with silver
before exposing it in the camera. The whole process
needed to be done while the plate was still wet,
which was fiddly and meant that taking a camera on
holiday was a major undertaking.
All of that changed when an American called George
Eastman invented the Kodak process in 1880. Many
photographers of the time were experimenting with
dry glass plates, and Eastman
developed a particularly effective
way of immobilising silver salts on
plates using gelatine – the same
protein that gives jelly its wobbly
consistency. The same silver
chemistry was needed to make the
sensitive silver halide salts, but the
plates remained just as sensitive
to light once they dried – as long
as they were kept in the dark.
It was Eastman’s next
development that really brought
photography to the masses –
flexible photographic film. After
1888 this meant anyone could buy a camera, take a
series of pictures, then send it back to the company
to be developed.
As photographic film became more complex,
introducing different compounds to make colours
and ever faster and finer quality crystals to make
sharper images, still relied on silver salts. These
salts were almost invariably prepared from silver
nitrate – its solubility and lower sensitivity to light
making it ideal for the job.
The connection between silver nitrate and light
doesn’t end there. If you want to make a glass surface
into a shiny, reflective mirror, one way to do it is to
coat the back side with silver metal. But how do you
get the silver on there? If you dissolve silver nitrate
in water and add sodium hydroxide, you form silver
oxide. Adding ammonia then converts this into a
diammine-silver(I) complex – a silver ion bonded to
two ammonia molecules. Adding sugar to this mixture
reduces the silver to its lustrous metallic form, and
deposits it on the surface as a perfect, shiny mirror.
All this is reminiscent of the Tollen’s reagent test for an
aldehyde, often called the ‘silver mirror’ test which you
may have done at school. It can be used to distinguish
between ketones and aldehydes, since aldehydes
are much more easily oxidised to carboxylic acids.
The reagent is initially clear and colourless but add
an aldehyde and the inside of the test tube is quickly
coated in a layer of shiny silver metal.
Check out the podcasts from Chemistry World. Each
week a leading scientist or author tells the story
behind a different compound.
www.chemistryworld.org/compounds
InfoChem
0511INFO - Magnificent molecules.indd 4
14/09/2011 16:01:59