Today we're doing the first in a series of tutorials covering some basic topics.

Topics that really are essential to understand.

When chemicals react together, they normally do so in certain ratios of atoms and molecules.

For example like one atom of sulfur and one molecule of oxygen reacting when sulfur burns, forming one molecule of sulfur dioxide gas.

Or two molecules of hydrogen and one molecule of oxygen reacting and forming two molecules of water.

Now you can't just create atoms out of nowhere. At least not using chemistry.

Subtitles by the Amara.org community

So it's important that any equation has the same number of atoms going in as going out.

It has to balance.

Finding an equation for the reaction you want to do, and checking that it balances is the most important first thing you need to do when planning an experiment.

Unless you do this you don't know how much of each ingredient to use.

Also, very importantly you'll know how much of your product you can expect to get.

The technical term for these ratios of molecules that react together is called stoichiometry.

In our hydrazine case we know that for every molecule of sodium hypochlorite bleach we use, we could in theory end up with one molecule of hydrazine.

Without looking up the equation we don't know this.

But there's a catch.

The catch is that in practice you can't count the number of molecules in any molecule.

There are in the region of 10 to the power of 23 molecules of any given chemical in any amount you'll be handling in a typical reaction.

That's 1000 times more than the total number of insects alive on planet Earth or the number of drops of water in all the oceans.

So you can't count?

But luckily for us there is an indirect way to count so that we can get the proportions of any chemical we need correct.

It happens that every single element has a particular weight.

Hydrogen atoms have a relative weight of approximately 1 unit.

Oxygen atoms have a weight of around 16 units.

Carbon is 12 units.

And so on.

And similarly, molecules made up of atoms simple have the weights that are the sum of the atoms they are made up of.

Water is opposite.

Oxygen plus 2 hydrogen.

So a total weight of 18 units.

So if you weigh out 2 grams of hydrogen molecules and 18 grams of water molecules,

you should have about the same number of molecules of each present.

Let's take a non-chemistry analogy.

Here's the very much desired kimple here Christmas hamper.

And your job is to make up the whole load of these two same molecules.

And then out to our closest friends.

In each hamper you've got 2 bottles of bleach for making your new year hydrazine.

You've got a bottle of spirits or when you screw it up because you were lazy and didn't use distilled water.

And obviously, a copy of the invaluable kimple here index.

Easy.

To make 10 hampers you need 20 bottles of bleach, 10 bottles of spirits, and 10 indexes.

But what happens if you have to order these components not by the number you want, but by the weight of each that you need?

Well, if you know what the weights are for each of the component units, then it's not too hard.

And even if you don't know the exact weights, but you know that relatively the bottle of spirits weighs twice as much as the bleach,

and the index a tenth as much, then you can still work with this.

You just order the weight that corresponds to the spirit.

The same number of units of each component, multiplied if you want a multiple of that component.

So in this case, 10 tons of bleach for 10 tons of spirits, because we need bottles in each hamper.

Hopefully this all makes sense so far.

So what's the chemistry connection you might ask?

Well we know proportionally how much of each chemical we want to react together from our equation.

We can't count the molecules, but we know that they have different weights.

So it's the same as the hamper problem.

Take the example with hydrogen and oxygen burning in a 2 to 1 ratio.

If we know the weight of a hydrogen molecule is 2 and the weight of an oxygen molecule is 32,

then we can work out how much of each we need to mix together for a complete reaction.

And this works really nicely for even compounds.

This is because the relative ratios for reactions are normally not very complicated.

And molecular weights can be worked out or looked up easily.

Suppose we want to brominate some propiothenone.

We can look up the reaction and easily see that one molecule of propiothenone will react with one molecule of bromine to form our desired product, bromopropiothenone.

So if you've got 134 grams of starch,

and you're starting propiothenone,

then you now know that you need about 160 grams of bromine to make this reaction work properly.

Or if you've got 10 grams,

then you need about 11.9 grams of bromine.

Because by weighing out these amounts,

we are measuring out roughly an equal number of molecules of each.

Because the atoms that make them up have different weights,

the relative numbers of molecules in a given weight of a chemical

rest in something called a molar amount.

In the example you see that when we calculated the relative number of molecules in 10 grams of propiothenone,

we got a ratio of the weight to the molecular weight which was 0.0745.

This is called the molar amount.

You can also say that you have a number of moles of a chemical.

One useful trick to remember is that if you have a number of moles of something,

the equivalent weight of the chemical just multiply this molar amount by the molecular weight.

Half a mole of propiothenone is 0.5 times 134.2 which is about 67 grams.

Now it might seem queer that 18 grams of water contains roughly the same number of molecules as 160 grams of liquid bromine.

But that's just the way it is.

You can't change the laws of physics, Captain.

Physics unfortunately always trumps chemistry.

But don't worry because maths trumps physics.

And because maths contains anomalies and paradoxes,

chemistry trumps maths.

So all is at harmony in the great scissors paper rock game of natural science.

But this has consequences.

Remember that if you're doing the reaction which you see,

which is a really heavy element somewhere,

that you'll need a lot of it by weight in order to have a lot of molecules present.

And if your product doesn't have a heavy element in it then you won't get much.

For example, if you want to make nitrophane from the reaction between silver nitrite and ethyl iodide.

Well you've got silver and iodine in there which are big heavy atoms.

Your equation tells you that these will react in a 1 to 1 ratio of molecules.

But if you take 10 grams of silver nitrite and the equivalent molar amount of ethyl iodide and react them together,

you're only going to end up with at best 4.9 grams of nitrophane.

Three quarters of the mass of your starting ingredients was made up of the heavy silver and iodine atoms.

And none of these are in your product.

You'll end up with 15.3 grams of fairly useless silver iodide.

It's annoying sometimes, but it's the way it is.

It's especially annoying because things like silver and iodine aren't just really expensive per gram.

When you consider that they're heavy atoms as well they're even more expensive per atom.

So our top tip is this.

Before you perform any reaction, draw up a table which lists out the chemicals you will use,

what you expect the products to be,

the ratios needed according to the equation,

and some other useful information.

Take your time and do it properly and it helps you think about things.

If you're dealing with solutions such as hydrochloric acid,

then things get a little bit more complicated in working out how much to use.

You have to then understand the concept called molarity of solutions and a little extra bit of maths.

It's not hard, but get the basics right first.

Well that's all for this tutorial and we'll get back to our Christmas ham for now

and coming up with lots more reactions for you soon.

We'll probably do a few more tutorials on basic topics in the future so stay tuned for these.

We hope this useful for you and at the very least you got to see some maths dissolving into Irania solution.

See you in the next one.

Bye bye.