InfoChem
Water for life
Tom Westgate investigates the chemistry and chemists
helping more people to access clean water
ISSUE 129 | JUNE 2011
In this issue
Glutamate
The source of delicious
savoury sensations
The Last Castle
Can a water cannon fire a
hook and chain?
Backyard chemistry
The science of Space Dust
A day in the life
Julian Huppert MP
Plus ...
ANDREA SCHAFER
Prize puzzles
How can you sum up the importance of water to life
on Earth? It covers 70% of the planet’s surface, makes
up 50 to 70% of the human body, and adults need to
drink around 2.5 litres every day. But still more than one
billion people, mostly in developing countries, cannot
access safe water for drinking, cooking, washing,
growing crops or rearing livestock, according to UK
charity Practical Action. Meanwhile one in eight people
in the world drink water that contains pollutants,
bacteria or viruses that are likely to make them ill,
according to US-based group charity Water. So how can
chemistry help to make water safe to drink, anywhere in
the world?
Safe supply
When you turn on the tap, the water that comes out has
come a long way since falling as rain and accumulating
in a reservoir or in groundwater (water contained
underground in soil and rocks). Depending on the
source, your glass of water may have been through
several purification steps to remove solid particles,
dissolved minerals and ions, chemical pollutants,
bacteria and viruses before it is safe to drink.
At a water purification plant, the first step is often to
clarify the water by removing microscopic (0.1 µm or
smaller) particles of dirt suspended in the water which
make it murky or cloudy. The dirt particles carry a
negative electrostatic charge on their surface, which
means they repel each other and remain suspended
instead of settling at the bottom of a container. To
remove the particles, chemicals called flocculants
are added to the water. Flocculants contain soluble
cations, which attract the negatively-charged particles,
neutralising their charge and allowing them to stick
together to form larger and larger clumps (flocs) which
Editor
Karen Ogilvie
Assistant editor
David Sait
Layout
Scott Ollington
Publisher
Bibiana Campos-Seijo
InfoChem is a supplement to
Education in Chemistry and is
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the Royal Society of Chemistry,
Thomas Graham House,
Cambridge,
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email: [email protected]
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© The Royal Society of Chemistry,
2011. ISSN: 1752-0533
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0411INFO - FEATURE_Water.indd 1
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eventually sink to the bottom of the flocculation tank.
The most common flocculant is potassium aluminium
sulfate, or alum, but other cations like iron, calcium
or magnesium, or positively charged polymers like
polydiallyldimethylammonium chloride can be used.
on the pore size). These unwanted substances are
trapped, and purified water can be collected on the
other side of the membrane.
‘Anything above 10 µm can be separated in a filter’
explains Professor Nidal Hilal, an expert on membrane
separation at Swansea University. ‘Anything smaller
Filtration
Filtration through sand, gravel and charcoal removes the can be separated with a membrane, from 10 µm to the
atomic level.’ Nanofiltration (using a membrane with
smallest particles, and chlorine is used to kill bacteria
pores of 1–5 nm) is used in Bangladesh, for example,
and viruses (decontamination), so the water that is
where some groundwater is contaminated with the
pumped to your tap is safe to drink. Even so, there are a
poisonous metal arsenic, and in Paris, to remove
range of products available to purify it even further.
pesticides from the water in the River Seine.
Water filter jugs can be bought in most supermarkets.
The filter cartridges contain activated carbon, a highly
porous form of carbon that has a very large surface
area capable of absorbing chlorine, pesticides and
other organic pollutants. The filter cartridges also often
contain an ion exchange resin that can reduce the
concentration of metal ions like calcium and magnesium
(which cause limescale when they precipitate out of
the water) as well as harmful heavy metals like copper,
lead, arsenic, chromium, radium, and uranium. The ion
exchange resin is made up of beads of a porous polymer
with sodium or potassium bonded to a negative group
such as carboxylate (NaOOC or KOOC). When water
passes through the bead, strongly positive metal ion
contaminants displace the sodium or potassium ions
and bond to the carboxylate group (COO–) on the resin.
The harmless sodium or potassium ions take the place
of the other metal ions in the water that drips out of the
filter.
A cross-section of a water
filter cartidge, showing
the activated carbon and
ion exchange resin
2
Atomic force microscope image of membrane pores,
showing a pore blocked with biocolloid.
NIDAL HILAL
Andrea Schäfer, a professor of environmental
engineering at the University of Edinburgh, designs
membrane purification systems and believes they are
particularly well suited for places where getting drinking
water is difficult. ‘For example in natural disaster zones,
where the infrastructure has been destroyed or was
never there, a membrane plant can be set up from a
container to start producing clean water straight away’
Schäfer said. Her research group has also set up a solar
powered membrane filtration plant in the Australian
outback. Closer to home, nanofiltration is used in
remote communities in Scotland where providing clean
water is a ‘major challenge’ according to Schäfer, due to
organic material from peat contaminating supplies.
Sea water and salty groundwater can also be turned
into a source of drinking water, thanks to membranes.
Particles smaller than 1 nm, such as salt, require a
process called reverse osmosis to separate them from
water. In this technique, salty water and clean water
are separated by a membrane. Normally, osmosis
would cause pure water to flow through the membrane
into the salty water, in order to dilute the salt further,
reducing the difference in concentration between the
two sides of the membrane. If enough pressure is
applied to the salty side, however, reverse osmosis
takes place: ‘you can push clean water back through
the membrane, leaving contaminants behind,’
explains Hilal.
Marvellous membranes
In some places, water supplies are contaminated with
specific compounds and require another purification
step. A common solution to this problem is to use a
membrane, a polymer layer with tiny pores that let water When water is scarce, waste water or sewage from
through but are too small to let through contaminants
the bath, shower or even toilet can be put to use
like organic molecules, metals, or bacteria (depending
and turned into drinkable water using a membrane
InfoChem
0411INFO - FEATURE_Water.indd 2
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bioreactor. These systems, which have been used
to treat drinking water in Singapore and Australia,
make use of the bacteria that are naturally present in
the sewage. ‘The bacteria eat everything available,’
explains Professor Schäfer, before a membrane is used
to filter out the bacteria and solid waste products.
‘The problem is people don’t like drinking it because it
started as sewage, but it can be better than tap water’
said Schäfer. Professor Hilal also believes we need to
re-think how we use water, by being less wasteful and
making the most of under-used sources like waste
water, flood water and rain water. ‘This is an extremely
important message, especially for young people,’ he said.
One way to remove organic compounds from water is
to use the highly reactive hydroxyl radical (HO•), which
is one of the most powerful oxidising agents known.
The so-called advanced oxidation technologies rely
on generating hydroxyl radicals in dirty water, which
then react with any contaminants, converting them
into harmless molecules. ‘Hydroxyl radicals will destroy
practically all organic compounds, forming carbon
dioxide and water’ explains Professor Gianluca Li Puma, a
chemical engineer at the University of Loughborough.
Hydroxyl radicals are formed when one of the covalent
O-H bonds in H2O breaks and the oxygen and hydrogen
atoms take one each of the bonding pair of electrons.
The resulting unpaired electron on the oxygen atom is
what makes the hydroxyl radical so reactive. The O-H
bond can be broken in a number of ways: by vibrating
it with ultrasound, by electrolysis, by reacting water
with ozone, or with hydrogen peroxide in the presence
of ultraviolet light. Li Puma’s team are developing a
method that uses solar energy to power the bondbreaking reaction. ‘The idea is to use photons to
activate a catalyst that can generate the hydroxyl
radical’ said Li Puma. The catalyst, made up of titanium
dioxide nanoparticles, is a semiconductor, which means
it has electrons available to absorb energy from light
(in this case ultraviolet light). These electrons become
‘excited’ and can move around the surface of the
nanoparticles, in turn leaving behind a positive charge
(or ‘hole’) which can oxidise water to form the allimportant hydroxyl radical.
Li Puma says the TiO2 catalyst reactor is most suited
to industrial applications, because of the cost of the
catalyst. But if more efficient catalysts that absorb
more light (especially in the visible spectrum) can be
developed the technology might become cheaper. This
ANDREA SCHAFER
Nice nanotechnology
In industry, treating waste water streams to remove
organic compounds such as pesticides and unwanted
pharmaceutical by-products is vital to ensure they
don’t enter the water supply. Research into solving
this problem has led to some interesting new
decontamination methods that could be applied in the
wider world.
could help to produce clean drinking water, especially
in developing countries where there is a lot of sunlight.
His group is currently working on a project to design
a reactor that goes one step further than destroying
organic pollutants, and could solve two environmental
problems at the same time. ‘The hydroxyl radicals
destroy the pollutants, but the electrons from the
catalyst can reduce water too, and produce hydrogen
that could be used to generate electricity in fuel cells,’
Li Puma explains. This could be a source of ‘green,
renewable energy, using only sunlight,’ said Li Puma,
who hopes to power the reactor’s water pumps using
solar panels, making it totally self-sufficient.
A solar-powered reverse
osmosis plant in the
Australian outback
As the population grows, the global water crisis will
become worse. The world will need to find new ways
of keeping drinking water clean and safe wherever it is
needed, and research by chemists will hold the key to
solving this problem.
Try it yourself
You can measure for yourself the quality of your local water, and compare
your results with those from around the globe by taking part in the world’s
biggest chemistry experiment. The global water experiment (part of the
International Year of Chemistry 2011) includes measurements of the salt
content and pH of a local water source, as well as a challenge to create the
most efficient solar-powered water purification still.
For more information go to http://water.chemistry2011.org/web/iyc.
InfoChem
0411INFO - FEATURE_Water.indd 3
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Magnificent molecules
Phillip Broadwith, Chemistry World features editor highlights one of his favourite molecules.
In this issue: glutamate
When you eat a rich tomato sauce, or a
hearty soup or stew, what makes it taste the
way that it does? Is it slightly salty? Is there
a hint of sweetness from the perfectly ripe
tomatoes? A tang of citrus sourness or a note
of herbal bitterness to add depth, perhaps?
All of these things might be present, but the
overwhelming taste of such a dish is usually a
luxurious, mouthwatering savouriness, which
accentuates the impact of all the aromatic
flavour compounds that are filling your nose
at the same time as your tongue revels in its
taste sensation.
But where does that savoury taste come
from? Traditionally in western cuisine, it was
thought that the tastebuds on our tongues
could distinguish four different tastes –
sweet, sour, bitter and salt. But in 1908, the
Japanese chemist Kikunae Ikeda identified a
fifth basic taste, which he called umami, from
the Japanese for ‘delicious taste’.
Ikeda noticed that the taste of many foods –
particularly kombu dashi, a seaweed broth
popular in Japan – didn’t really fit into the
sweet, sour, bitter, salt categorisation.
Eventually he discovered the molecule
that was responsible for the seaweed’s
palatability – glutamate.
Certain foods are naturally high in
glutamate, such as tomatoes, mushrooms,
cured meats, fish and cheeses like Italian
parmesan or French roquefort. But it is
particularly enriched when these foods are
cooked slowly for a long time or fermented.
This is why stocks and broths, or soy
sauce and tomato ketchup are particularly
intensely flavoursome. Ingredients such as
Asian fish sauces or the quintessentially
British Worcestershire sauce and Marmite
yeast extract have especially high levels of
glutamate. And even the ancient Romans
reportedly used a fermented fish sauce
called garum to season food and enhance
its flavour.
The MSG debate
The sodium salt of glutamic acid is called
monosodium glutamate, or MSG. It was
developed as a food additive and flavour
enhancer following Ikeda’s discovery, and
quickly gained popularity as a cheap way to
boost the flavour of food made with lower
quality ingredients.
Takeaway Chinese food in the UK and US
gained a particular reputation for using MSG
to enhance flavour. In fact, pretty much any
processed fast food is likely to contain added
MSG, unless it specifically says otherwise.
But is it bad for you? Glutamate is a natural
component of proteins, and there is
chemically no difference between ‘natural’
glutamate and that added in the form of
industrially produced MSG. There have been
various arguments that MSG is bad for us,
even the suggestion of a medical condition
called ‘chinese restaurant syndrome’ or
‘MSG symptom complex’ caused by eating
too much MSG. But the medical evidence is
unconvincing. Like any chemical, if you eat
large enough amounts, it is not likely to do
you much good, but at the levels even the
most junk-food-hungry among us are likely to
ingest, there is no indication of health risks.
So the next time you are in a restaurant,
whether you’re grabbing a cheeseburger
or sitting down to a sumptuous ten
course Michelin-starred tasting menu,
take a moment to savour the taste. That
indescribable savouriness that leaves your
mouth watering and your tastebuds begging
for more. That’s the umami tingle that
comes from glutamate – be it from the finest
culinary ingredients or straight out of the
bottle marked MSG.
Originally published as part of Chemistry World’s
‘Chemistry in its element’ podcast series at:
www.chemistryworld.org/compounds
Deliciousness
Glutamic acid is one of the twenty standard
amino acids that make up proteins. Its
systematic name is 2-aminopentanedioic
acid – a five carbon chain with a carboxylic
acid group at either end and an amine (NH2)
group attached to the carbon adjacent to one
of the acids.
When glutamic acid is incorporated into
proteins, the side chain that sticks out from
the protein backbone is a short three-carbon
chain ending in a carboxylic acid. But under
the conditions in our mouths, one of the
acid groups is normally ionised to make a
glutamate anion, and it is this that binds to
umami taste receptors on our tongues to
produce that delicious savoury sensation.
InfoChem
44InfoChem
0411INFO - Magnificent molecules.indd 4
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Feature
Heading
On-screen
science
Heading in here
The Last Castle – can a water cannon fire
a hook and chain?
PICTURE CREDIT
Jonathan Hare explains...
The Last Castle (Robert Redford and James Gandolfini)1
is about unrest and rioting in a military prison. In one
rather dramatic scene the prisoners capture a highpressure water cannon and use it to blast a grappling
hook and chain into the air to capture a low flying
helicopter. A prisoner then climbs up the chain and takes
over control! It looks fantastic but could it really work?
State-of-the-art water cannons2 can hold 9000 litres
of water, pump 900 litres per minute at a pressure of
about 1400 kPa and shoot a jet 75 m! The speed and
weight of the water can easily knock people over and
cause bruising, so you would think that the movie stunt
would be very feasible.
If you ram a cork into the end of a garden hose and
turn on the water, any trapped air in the tube will be
compressed by the incoming water. The air will store
up energy like a spring, until the friction of the cork is
overcome, popping it out and sending it flying. This is
how a spud gun or air gun works and partly how a toy
water-rocket works. In the film clip however, the hook is
just slotted into a tube at the end of the cannon and it’s
very unlikely to be a good air-tight seal. In this case the
air pressure won’t be able to build up and the grappling
hook will be driven out only by the initial force of the
water hitting it.
GETTY IMAGES
If the end of the firing tube narrows, the restriction
will speed up the water and the resulting jet will go
much further. The increased velocity may provide more
momentum to the hook, however once the water is
free from the hose it will spread out and the pressure
will drop. As only a fraction of the water will now
interact with the small end of the hook it will receive
relatively little momentum from the water. So even
though the water jet may go a long way, the hook will
action of trapped air, the cannon just wouldn’t work for
tend to drop down.
projecting anything other than water.
A few years ago we tried this out on a slightly smaller
References
scale.3 We found that the water jet went a long way
1 The Last Castle, Dreamworks, 2002
just as you see in the film clip, but unfortunately the
2
To see a water cannon in action see the links on:
grappling hook only went a metre or so. In the film a
http://bit.ly/jYXq9V
long metal chain was attached to the hook which would
3
Hollywood
Science, series 2, J P Hare, R Llewellyn,
have been very heavy and have made the situation even
BBC
/
OU
TV,
2004
worse. Overall we found that without the spring-like
InfoChem
0411INFO - On screen chemistry.indd 5
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Did you
know?
The urban legend that Pop
Rocks and Space Dust
caused your stomach to
explode forced the US Food
and Drug Administration to
set up a hotline to reassure
anxious parents.
Backyard chemistry
Prof Hal Sosabowski presents
experiments you can do on your own
HALA JAWAD
In this issue: the science of Space Dust
Backyard science regularly
examines the properties of
confectionery. The experience
of eating food in general
but sweets and desserts in
particular, is a combination of
taste, smell and mouthfeel.
Taste and smell combined
are known as flavour, which
curiously is much more smell
than taste. Mouthfeel is all
about texture. For example
the creaminess of ice cream
is caused by the particle size
of both fat particles and ice crystals. If these are too big, the
ice cream loses its creamy texture and feels rough. Some
of the qualities that describe the concept of mouthfeel
include: brittleness, crumbliness, crunchiness, density,
viscosity, smoothness, and uniformity of bite/chew.
Some sweets rely almost solely on mouthfeel and have little
if any taste. Sherbet tastes tart and fizzy since it contains
citric acid (tart) and releases carbon dioxide (fizzy).
Health &
Safety
There are no particular health
and safety issues connected
with this experiment.
This article is based on an
idea originally seen at Steve
Spangler Science.
6
Space Dust is a rocky type of bagged sweet which was in
vogue in the early 1980s. Although it is supplied in various
flavours, like sherbet, it relies mainly on mouth sensation
for its uniqueness. The sensation experienced when
chewing Space Dust is of very small detonations (pops) in
your mouth. This led to an urban myth that when Space
Dust eaten along with some fizzy drink, there was a risk of
your stomach exploding! This led to it being temporarily
discontinued in 1983 in the US.
In this experiment we will demonstrate that a small crystal
of Space Dust contains more than its volume of carbon
dioxide. This is possible due to the manufacturing process
which causes pressurised carbon dioxide to be trapped
inside the crystals of space dust.
Materials
You will need:
Space Dust (available on ebay or Amazon, branded as
Fizz Wizz, 10 packets for about £1.40 + postage)
tablespoon or a pestle and mortar
0.5 l bottle of fizzy drink
balloon
narrow-mouthed jar.
Method
Experiment1:
Eat some Space Dust and feel the pop when you chew
the rocks.
Experiment 2: crushing Space Dust
Place some crystals on a hard surface or in the mortar
and crush them with the back of the spoon or the
pestle. As the crystal ruptures, the carbon dioxide
rapidly escapes causing a pop. This is directly analogous
to a balloon popping.
Experiment 3: measuring the amount of CO2 in Space Dust
Pour a bag of Space Dust into the empty balloon. Attach
the balloon to the neck of the full bottle. Don’t let the
Space Dust fall into the liquid. When the balloon is
attached, lift up the balloon to allow all of the Space
Dust to fall into the drink. The balloon should inflate.
The science
Space Dust contains sugars (sucrose, lactose, glucose,
artificial flavour, and carbon dioxide). The sweets are
prepared as any other, by melting the sugars and
fusing them into rocks/crystals but this is done under
fairly high pressure of carbon dioxide (4140 kPa) which
causes bubbles of pressurised CO2 to be trapped
within the crystals.
Curiously, you may have noticed that the balloon
doesn’t inflate very much and conclude that there isn’t
much CO2 within the packet of Space Dust. You would be
correct. But there is even less than this experiment has
shown. Adding anything with rough edges to fizzy drink
causes the dissolved carbon dioxide to come out of
solution more quickly. Most of the CO2 in the balloon is
from the fizzy drink and not from the Space Dust. So,we
have conclusively demonstrated the low likelihood of
Space Dust eaters’ stomachs exploding and debunked
an urban myth!
InfoChem
0411INFO - A day in the life of.indd 6
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A day in the life of
Julian Huppert
Member of parliament
for Cambridge
Julian has been MP for Cambridge since 2010.
Before this he was a fellow in computational
biology at the University of Cambridge.
He spoke to David Sait about his work.
From the lab to the debating chamber
Julian originally trained as an organic chemist. He
gained a PhD in biological chemistry then had a
position as a research scientist at the University of
Cambridge. His research looked at the structures
formed by nucleic acids, providing an insight into the
various functions they perform.
Outside of science, Julian has long been politically
active as a member of the Liberal Democrat party,
including being a county councillor for eight years. In
2010 he was elected as the member of parliament for
Cambridge.
Julian’s time is split between his constituency in
Cambridge and the Houses of Parliament in London,
and so a typical day depends very much on where he
is working.
Life in London
A day in London may start with attending a committee
hearing. Julian sits on the House of Commons Home
Affairs Select Committee, which reports on the work
of government departments and covers areas such
as immigration, policing and drugs policy. The work
of a committee includes discussing reports, receiving
evidence and questioning witnesses.
Meetings and committee work continue into the
afternoon, and during this time the House will start to
sit. Julian will try to get into the debating chamber to
ask questions and contribute to the debates, which
conclude with a vote at around 10pm.
With his background as a research scientist, Julian has
been able to speak knowledgably during recent debates
on drugs policy, arguing for scientific evidence-based
approaches to legislation, and also on collecting tissue
samples as alternatives for animal experimentation in
scientific research.
2010–present,
MP for Cambridge
2007–2010,
academic fellow at the
University of Cambridge
2005–2007,
postdoctoral researcher at
the Wellcome Trust Sanger
Institute
2001–2005,
PhD in biological chemistry
at the University of
Cambridge
1996–2000,
BA MSci in natural sciences,
University of Cambridge
1994–1996,
A-levels in mathematics,
further mathematics,
physics and chemistry
at The Perse School,
Cambridge
Julian’s experience as a scientist is also useful in the
more general work of parliament, eg lobbying for
more money for science in the budget, arguing for the
recognition of PhD qualifications in the immigration
process, or contributing to the debate on libel reform.
As a scientist, Julian is prepared to change his mind if he
receives new evidence. He says that this is rarely seen
in other politicians, as changing your mind is usually
interpreted as a sign of weakness.
Working in Cambridge
Every Friday Julian works in Cambridge. He may spend
the morning visiting schools and companies but much
of his time is spent in his office attending to casework.
Constituents write to Julian asking for his assistance
on a wide variety of matters (such as tax, housing and
immigration) and every letter receives a reply. Any
constituent can make an appointment to see him at
his surgery. Last year Julian and his team dealt with
5500 cases.
Most of the queries his constituents bring are not
scientific in nature, but Julian can use the skills in
problem-solving and analysing evidence he has
developed as a scientist to help to resolve a case.
oChem
You can download InfoChem at www.rsc.org/inf
and copy it for use within schools
0411INFO - A day in the life of.indd 7
Pathway to
success
MP for a
week
If you’re interested in the
work of MPs, you can have
a go at being an MP for a
week in the new game from
the parliament education
service –
http://bit.ly/kL1SL8
InfoChem
7
25/05/2011 16:08:58
Chemical acrostic no. 20
£50 of tokens to be won
Puzzles
Students are invited to solve InfoChem’s acrostic puzzle contributed
by Simon Cotton. Your task is to complete the grid by answering the
nine clues on the earth’s crust and atmosphere to find the answer in
the shaded box, which is an important metal ore.
Prize wordsearch no. 57
Find the 31 words/expressions associated with valency hidden in this
grid contributed by Bert Neary. Words read in any direction, but are
always in a straight line. Some letters may be used more than once.
When all the words are found, the unused letters, read in order, will spell
a further 9-letter word.
Please send your answers to the editor at the usual address to arrive no
later than Monday 11 July. First correct answer out of the editor’s hat will
receive a £25 Amazon gift voucher.
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ETHANE
FORMULA
FRACTIONAL BONDS
FRAMEWORK
GRAPHITE
HALF BONDS
HYDROGEN ATOMS
IONS
1. Essential process in the carbon cycle.
2. Abundant metallic element, essential in the structure of the human body.
3. Life-giving element in the atmosphere.
4. Most abundant metal in the Earth’s crust; marathon runners sometimes
cover themselves in sheets of it to keep warm.
5. Element found in all fossil fuels.
6. A little of this is good for plants, but too much can be bad for rivers.
7. Second most abundant metal in Earth’s crust; found in our red blood cells.
8. If a mineral fizzes when acid is added to it, then it is probably a ______ .
9. The Earth’s gravity cannot hold onto this, so there is none of it in the
atmosphere.
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Please send your answers to: the editor, Education in Chemistry,
Royal Society of Chemistry, Thomas Graham House, Cambridge
CB4 0WF, to arrive no later than Monday 11 July. First out of the
editor’s hat to have correctly completed the grid will receive a £25
Amazon gift voucher.
NON INTEGRAL BONDS
NON MOLECULAR
OXIDE
OXYGEN
PERIODIC TABLE
SELENIUM
SELENIUM DIOXIDE
SILICON
THEORY OF VALENCY
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Chemical
acrostic no. 19
solutions and
winner
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The winner was
Max Haughey from
Burgate School and
Sixth Form Centre.
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May prize wordsearch no. 56 winner
The winner was Paul Hutchinson from Netherhall School. The 8-letter word was FELDSPAR
Name
School name
School address
Your email
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