Getting Sorted

It’s one of those common questions – how does the science you do in the classroom work in real life? Here’s how density crops up every day, as we all try to be a little greener…

You will need:

Different plastic cartons such a milk bottle, yoghurt pot, washing up liquid bottle
Scissors
A large bowl of water
A tablespoon
Salt

What to do:

Check the code on the bottom of your containers. There should be a number inside the triangular recycling symbol; for example a plastic milk bottle is code 2 or HDPE
Cut out three strips, about 1cm x 4cm, from each plastic container.
Fill the bowl with water and place the strips in it making sure they are fully immersed. Try adding washing up liquid if the strips cling to the surface.
One set of strips will float to the surface immediately. Remove these strips.
Now add a large tablespoon of salt to the bowl and stir it up so that it dissolves. You may need to keep adding more until another set of strips float to the surface. Remove these strips.
There should be one set of strips still sitting at the bottom of the bowl.
Congratulations! You have now successfully sorted three different plastics!

What’s going on?

Each plastic container is made of a different plastic, and has its own 'density'. Density is the measure of how heavy something is for its size, in other words its mass per unit volume.

Water has a density of 1 g/cm3, and anything with a density greater than this will sink in water; anything with a lower density will float. So if we have a plastic with a density less than 1 (e.g. the milk bottle) it will float in water.

Adding the salt to the water makes it more dense. That's why we float more easily in the sea than in a swimming pool. The yoghurt pot has a density slightly greater than 1 g/cm3, so it doesn't float in tap water but it will float in salt water. The washing up liquid bottle however has a higher density still, which means that it won't float in either tap or salt water.

This is how they sort plastic for recycling, which is why you can drop all sorts of different cartons into one enormous skip!

Funny but serious

A couple of weeks ago Mr Moakes and I were showing the Year 7 students the dangers of smoking as part of their tutorial programme. Did you know you can find arsenic and polonium in cigarettes? This site tells you about all the 4000+ different chemicals in cigarettes. Click the image left to watch a very funny video (with a serious message) about the damages of smoking. (2Mb)

What Happens When the Arctic Melts?

We don’t often see frozen sea water, but, of course, that is what the north pole is! Ever wondered what would happen if the Arctic ice cap melts? Here is a clever demonstration which shows you just that!

You will need:

A drinking glass
Ice
Marker pen
Ruler

What to do:

Fill a glass three-quarters full with water and add ice. Mark with your marker pen a line along the water level and measure the height from the bottom of the glass to the line, then wait for the ice to melt…
Once the ice melts, mark the new water level line and measure the new height from the bottom of the glass to the line. There should be a small drop in water level.

What’s happening?

Ice (unlike most other things) is actually bigger in its solid form than in its liquid form, and so it shrinks as it melts! The result of this experiment means the melting of sea ice has nothing to do with rising sea-levels - but global warming does lead to a rise in sea-level.
This is because even though water is unusual and expands when it freezes, it still expands when it warms up. The global rise in temperature has meant the water in our seas has got bigger, and so the overall global sea level has risen because of this.

Melting of land ice such as in the Antarctic also leads to a rise in sea-level!

Magic or Science?

With chemistry week sadly fizzling to an end, I came across this site all about the 'darker' side of Sir Isaac Newton. A brilliant mathematician and physicist, did you know he was also into alchemy? In fact during this period in history he was not the only scientist in pursuit of making gold from other chemicals, Robert Boyle, John Locke, Leibniz and many others were trying. Read an interview with Historian Bill Newton on Newton's alchemy on this link. Also have a look at this nice flash site that decodes Newton's notebooks. I wish I had a similar tool for Zak's physics homework.

Fire Extinguisher!

Activity: Putting Out the Light

If you are off to enjoy the fireworks displays this weekend, you might feel inspired to try some fire activities of your own, or perhaps you are wondering about the best way to put the flames out!

You will need:

Small candle (like a nightlight) and matches
Vinegar, hot water (from the hot tap) and bicarbonate of soda
A jug with a lip that you can pour from
Another container to mix the water and vinegar

What to do:

In your container, prepare a hot water and vinegar mix, (50-50 of each).
Light the candle.
Put about a dessertspoon of baking powder in your jug, then pour on the vinegar-water mix.
Let the fizz subside for a second or so, then take the jug and carefully ‘pour’ the carbon dioxide produced in the fizzing, over the candle. It will go out, ‘suffocated’ by the lack of oxygen.

What’s going on?

A candle burns in oxygen, combining oxygen with the chemicals that make up the candle wax creating water, carbon dioxide and a bunch of other bits and pieces. If you remove the oxygen, or displace it, the candle will go out.
The mix of baking powder and vinegar produces carbon dioxide gas in the fizzing that you see. Carbon dioxide is heavier than air so when you lean the jug over the candle carbon dioxide pours out and sinks onto the flame extinguishing it.
This experiment comes from Planet Science’s Little Book of Experiments – have a look here for more science things to do with candles and other stuff you’ll find in your home.

You could be a winner!

To celebrate Chemistry Week and all things elemental there is an elementary quiz on this link - enter and you have the chance to win a one of three ‘Tungsten’ T’s, RSC goodies and copies of Bill Bryson’s ‘A Short History of Nearly Everything’. Remember the clues are in the questions! On the chemistry theme (and of course November 5th Guy Fawkes/Bonfire Night) - take a look at this fireworks website - it is one of the best I have seen - lots of flash animations on how they work and videos of the different types, you can even play around in their virtual fire lab, rearrange some molecules and find out the temperature of a striking match. The practical of the week is interestingly all about putting fires out quickly!

Nothing to do with Science

Here is food for thought, type the word 'failure' into the google search box to the right and see the top link!