presents
Quite
Interesting
Science
This week:
Snow and ice
1 Is it possible to walk across the
English Channel?
1
2
It would be – if it was frozen. But will
this ever happen?
We all know pure water freezes at 0 ºC.
But salty water doesn’t freeze until it
gets even colder.
There is a lot of water in the channel.
It would take ages for all the particles
to get into a regular pattern and form
ice. So it would need to be very cold
for a very long time to freeze the
channel.
2 Why spread grit on icy roads?
1
2
Grit is actually rock salt – impure sodium
chloride. So how does this compound
help?
It lowers the freezing point of water.
What salt dissolves, its ions attract water
molecules. That makes it harder for water
molecules to form crystals, so water
freezes at a lower temperature.
3 Why not use sugar on icy roads?
Anything that dissolves in water will
lower its freezing point, so you could use
sugar. But salt is NaCl and glucose – the
simplest sugar - is C6H12O6. Why is this
important?
Sodium chloride has a smaller formula
mass than sugar, so there are more
particles per tonne of sodium chloride.
The more particles, the bigger the effect
on water’s freezing point.
4 It's 4'C today, so how come
there's still snow on the ground?
Melting takes time. It’s the same
with ice-cream. Why?
Water molecules have to absorb
energy to overcome the attractive
forces holding them in place.
Absorbing enough energy
takes time.
5 The road is ice-free…
…but in 10s the driver
will skid over the side
of a bridge! Why?
Bridges get icy (and slippery) before
the roads on land. Why is this?
Modern bridges contain a lot of metal.
Strong metallic bonding gives bridge
supports high tensile strength.
Delocalised
electrons make
metals good
conductors,
so they lose
heat quickly.
6 His diesel car has stopped
working…
…but the petrol
cars on the road
are fine.
Why?
The hydrocarbon chains in diesel
are longer than those in petrol.
What difference does that make?
Diesel has stronger intermolecular
forces so it is less volatile than
petrol.
Some of the compounds in diesel
freeze around -15 ºC. It has to be
much colder to freeze petrol.
7 You throw water up - snow
comes down. How come?
The air has to be cold – very cold.
In Siberia it is –40 ºC. What
happens to the water in the air?
It freezes instantly as water
molecules lose energy and fit
together to form crystals.
Throwing it up helps by forming
droplets. Their large surface area,
makes them lose energy faster.
8 When can water pack a
bigger punch than a boxer?
Water is a simple molecular substance.
So why is frozen water so hard?
Covalent bonds are strong,
but intermolecular forces
are weak. So most simple
molecular solids are soft.
But the intermolecular forces
in ice are quite strong, so ice
is harder than most simple
molecular solids.
very strong
covalent
bond
intermolecular
force
9 Why doesn’t this frog need
to stay warm?
If you stayed out in freezing
weather for too long, you would die.
But wood frogs can survive. How?
They fill their cells with sugar. This
acts like antifreeze to stop them
freezing solid.
The frog’s antifreeze stops ice
forming the same way salt stops it
forming on roads.
10 Why is water strange?
solid water
liquid water
If this was any other substance,
the solid state would sink.
So why do icebergs float?
When most substances freeze,
their particles get closer together,
so they get denser.
Water is strange because the
particles in ice crystals are more
spread out, which makes it less
dense than water.
11 Santa has a new sledge. Its
made of plastic. Is this a
good choice of material?
1
2
Plastic is lightweight so it’s easier for
reindeer to pull, but will it survive a
subzero Christmas Eve?
Maybe not! Plastic particles are like
strands of cooked spaghetti. They slip
and slide over each other to make a soft,
flexible material.
But when the temperature drops,
particles lose energy and stick together.
The plastic goes rigid and brittle like
glass. Any small pushing force could
make the sledge shatter.
THE END
No
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answer
Yes. Use the
Channel Tunnel
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answer
Grit is dark. So it
absorbs more
sunlight and melts
snow.
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answer
Grit increases
friction so cars
don’t slide.
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answer
It would make
them sticky.
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answer
Snow melts at a
higher temperature
than ice.
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answer
Bridges aren’t
gritted.
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answer
It can’t.
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answer
It can’t feel the
cold.
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answer
It’s not.
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answer
It’s not.
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answer
Yes
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answer
No
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answer