It’s 2014, and the internet is bursting with high-quality free fonts. But lots of educators and students still write up documents in drab default fonts like Calibri, Cambria, Times New Roman, Arial and even [shudders] Comic Sans. This is understandable: they’re free, they’re on every school computer and they work. But can we do better? If you prepare work on a computer you can install fonts on, absolutely. Here’s some alternatives. They’ve been chosen for being comprehensive but easy to download and install, and because they will make your work stand out clearly from the crowd. Continue reading
GETTING IT 100%
Say you know that you’ve drunk half a bottle of water, and you’ve drunk half a litre of water.
It’s not hard to work out that the bottle’s a one-litre bottle of water.
But what if the percentage is something a bit more complicated?
Say you’ve drunk 28% of a bottle of water, and you’ve so far drunk 421ml?
This is a potential exam question in chemistry.
The maths is a standard formula, and it’s simplest to just learn it and practice with a few examples. Continue reading
Let’s start by summarising how things get through cell membranes.
- Oxygen, carbon dioxide and water:
These can get through cell membranes without any help, by simple diffusion. The way water diffuses through a cell membrane is called osmosis, which is a word you can only use to describe water moving.
- Food chemicals and minerals:
These can’t get through cell membranes without help. They need to go through using carrier or channel proteins.
Most chemicals in the body are hydrophilic: they dissolve in water and they want to be in water. The cell membrane’s centre (where the hydrophobic fatty acid tails are) is hydrophobic: it’s like vegetable oil. Most chemicals in the body can’t get through it easily without help.
This is what’s meant to happen. Cells want to control what enters and leaves them. They’d die instantly if all their food could just fall out of them! Continue reading
For A-level biology, it’s important to make sure that your learning and revision plans cover the whole course, missing nothing out. That makes the specification a great free, compact revision guide. Here are direct links to the current biology syllabuses, with page numbers for the course descriptions for the modules taken by exam.
- AQA specification. AS-level: pages 6-22, A2 pages 23-37.
- OCR specification. AS-level: pages 8-26, A2 pages 27-47.
- WJEC specification. AS-level: pages 12-17, A2 pages 18-26.
- Edexcel specification. AS-level: 26-35 & 52-63, A2 38-48 & 66-77.
At AS-level, OCR asks you to learn about three very nasty diseases. They’re on the course for a reason: they’re all dangerous and hard to treat.
And each is caused by a different type of pathogen, so they were chosen so you learn what kinds of microbes cause disease. Let’s start with the basic facts:
The most important things in this post:
Malaria: Spread by female Anopheles mosquitoes. The pathogen is a protozoan named Plasmodium. It infects your blood cells and liver. Could be spread by global warming.
TB: A bacterium. Spread by coughs and sneezes. Antibiotic resistance is making it harder to treat.
HIV: A virus. The disease it causes is AIDS. It destroys your helper T-cells. It’s spread by sharing needles and unprotected sex. People can pass it on without knowing they have it.
And now here’s the rest of it:
This is a topic Edexcel really care about. They ask questions about it every year. But those questions can come up in lots of places, because this is a topic that joins up many parts of the course. This article is about what they’re looking for.
Acid rain is nasty stuff, and you need to know what it does: you can’t just say it’s bad!
It’s made when people burn fossil fuels. Sulfur in petrol and coal burns and turns into sulfur dioxide gas:
This reacts with water in the air, turning into a chemical a lot like sulfuric acid in rain:
You need to know both these equations. (Which is kind of sad, since the bottom one actually isn’t quite right. But you won’t find out why unless you do a chemistry degree.)
Sulfur dioxide is also an irritant. It makes your throat itch, and if you have asthma it makes it worse.
Also, in a hot petrol engine, nitrogen in the air reacts with oxygen to make two chemicals called nitrogen oxides:
(You might also see these called NOx, because they’re a mixture of NO2 and NO. Remember them as NOxious, because they are!)
They’re also irritants, and can react with water in the air to make nitric acid.
How can you stop this? First, you can take sulfur out of petrol, and oil companies do. You can’t do that with coal, since it’s solid, so coal power stations have scrubbers on the chimneys that take it out.
What about the nitrogen oxides? They get taken out of the exhaust using catalytic converters.
Incomplete Combustion: Carbon Monoxide
When fuel isn’t burned properly, there isn’t enough oxygen to react with all the carbon in the fuel. An invisible but very toxic gas called carbon monoxide forms. (This is how it would form from pure carbon.)
It’s toxic, but why? Edexcel want you to explain that in a very specific way, and you need to say everything on the line below.
“Carbon monoxide reduces the amount of oxygen the blood can carry.”
Let’s cross over to biology: why’s that dangerous? Well:
“Cells in your body don’t get oxygen through the red blood cells, so they can’t do aerobic respiration, and they can’t get the energy they need.”
Saying all this is important, because they want to see that you know:
- Where respiration happens (every single cell in your body)
- Why you need to do it (to get energy out of food)
- What type of respiration needs oxygen (aerobic)
- How oxygen gets through your body (in the red blood cells).
Remember, Edexcel’s examiners have a specification of what you need to show you know. Make sure you tick each and every box on it.
Carbon monoxide also gets taken out of car exhausts using catalytic converters.
Incomplete Combustion: Unburnt Carbon
Incomplete combustion of fossil fuels also produces unburnt, pure carbon: little black particles of soot. It’s another irritant, and makes buildings look grimy.
Cutting the costs of chemical reactions:
Let’s start with catalysts. They:
- speed up
- a chemical reaction
- without getting used up
But they also let you do reactions at a lower temperature. That’s because they:
- provide a different reaction pathway
- with a lower activation energy
Why’s that important? You don’t need to use so much fuel heating everything up. Less carbon dioxide in the atmosphere, less global warming. And it saves money. Is this important? Absolutely. It’s not on your course, but here’s an article about a recently developed way to make ethanoic acid (the sour taste in vinegar) at a lower temperature than before. It’s a process that depends on using a complex new catalyst.
Your council collects scrap metal like drinks cans, old bits of computers and electronics, and recycles it. Good for the environment, and a classic exam question.
Why? Getting metals out of the ground is expensive. It uses lots of energy to extract them. And it causes global warming:
- Getting low reactivity metals out of the ground in blast furnaces uses coal. That causes global warming.
- Getting high reactivity metals out of ores uses electrolysis of molten ore. You need lots of electricity and lots of heat.
Recycling metals uses far less energy. And many of the metals in electronics are toxic, so recycling them is important: you don’t want them leaching through the ground where they’re dumped into water supplies.
How can you remember about recycling metals? Well, copper used to be cheap, but as people use more computers, which have lots of copper in them, it’s got pricier. In fact, criminals tear down live power cables to steal them. Insanely dangerous, and really bad for your town. Want to stop them? The next time your computer or phone breaks, make sure it gets recycled properly. You can find out how to do that here.
Plastics don’t rot down, or biodegrade. That’s bad news, since they can trap animals and kill them.
Why don’t they rot down? Well, let’s cross over to biology. Biodegrading is when things are broken down by decomposers: microbes in the soil. They do that using enzymes, and they often haven’t got any that are the right shape (have the right active site) to break down plastics.
Back to chemistry: plastics designers haven’t helped. Plastics are made to be inert: they don’t react with many things. That’s good news for people, because it means when you put things in them (like tomato ketchup in a bottle) they don’t react with the plastics to make toxic chemicals. But it’s bad news for the environment, since it makes them hard to break down.
You’ll see this in the news: the UK government recently put a tax on plastic bags, to try to make people use them less. And people have tried to design new kinds of plastic that decompose eventually but not while you’re using them. But again, the solution is probably more recycling. Next time you buy a drink in a plastic bottle, make sure you put it in a recycling bin. It’ll help you do better in your exams.
Renewable resources (triple):
Anything made from oil is a non-renewable resource: once we’ve burned it, it’s gone.
Sugar cane, bread flour and everything else made from plants is renewable: if we want some more, we can grow some.
This comes up for people doing triple, in making ethanol.You can make ethanol from sugar cane with help from yeast (renewable) or ethene from oil (not)
There are good and bad things about both methods:
- The ethene process makes lots of ethanol, and it comes out almost pure.
- That’s great for chemical factories that need pure ethanol.
- The sugar process makes ethanol with water in it: not so helpful.
- Why can’t the yeast make more? They’re microbes. High levels of ethanol start to kill them.
The sugar cane process is great for countries like Brazil, which have lots of fields of sugar cane. It also doesn’t contribute to global warming like using ethene.
For beer and wine, it’s good enough, though. People seem to get a bit freaked out by finding their drinks were made from crude oil, anyway.
Revising topics like this, that cut across many different areas of the course, is great practice. That’s because you remember things by connecting them up. The more things a topic is connected to in your mind, the more likely you are to remember it.
Terylene. Heard of it? I’d guess not unless you do A-level chemistry. But strangely, A-level chemistry examiners are obsessed with it. AQA, Edexcel, OCR. Here’s a bit about it, and then we’ll look at its chemistry.
Terylene is a plastic, just one of many.
Back in the 70s to 90s, clothes were made out of artificial fibres (plastic) a lot more than they are today. So much so that artificial fibres had brand names so you’d see them as a trademark of quality. Terylene was one of them. A famous writer had fun writing a poem praising the indestructibility of Terylene ties.
Sadly, clothes made of plastic stopped being fashionable a long, long time ago. By 1996, a top-ten hit used Terylene clothes as a synonym for ‘slimy and fake’. I asked my dad what came to mind when he heard the word: “Old blankets.”
So why do examiners love asking about it? And think Terylene is its ‘common name’? I have no idea. Maybe one of their mums invented it. But they do. It’s mostly called PET now, and used to make the trays of ready meals.
So why am I learning about it?
Speculation aside, Terylene is a condensation polymer. Specifically, a polyester.
Condensation polymers are plastics made from chemicals that react together to give two products: the plastic, and some small molecule, often water. In the case of Terylene, it’s water.
Polyesters are molecules in which the monomers are held together with ester groups.
So the monomers in Terylene are double ended. And there are two of them. One is a double-ended carboxylic acid, benzene-1,4-dicarboxylic acid, the other a double-ended alcohol, ethane-1,2-diol.
(they show you a diagram of Terylene)
· What type of plastic is this? (A polyester)
· Give its common name. (Terylene)