Concentration

Hi, hmm concentration of hydrochloric acid, sodium hydroxide blah blah is all around us when we look at chemistry worksheets.

So how to understand what does concentration really mean?

Imagine that you have a pot of OOO tea and you would like to sweeten the drink so that it taste better.

So you poor some tea from the pot into a nice cup that contains perhaps 100cm3 of OOO tea.

The next thing you would do is to put in some sugar cubes.

And then you STIR the tea.

Here we PAUSE. Why do you need to stir the tea?

Answer: So that the sugar will dissolve in the tea.

Moving on, you sample the tea.

PAUSE. What makes you think that the tea taste the same throughout the cup?

Answer: The ACTION OF THE SOLVENT which is our good friend water spreads the sugar cubes out equally throughout the water in the cup. (The key thing here is the solvent, it really spread things out evenly)

Moving on right, the taste of the tea does not agree with you. You have 2 choices, which will make the tea sweetest?

1) pour away two thirds of the tea in the cup and add in a sugar cube

2) add 3 sugar cubes  

The correct answer is…

 

BOTH are just as sweet. 🙂

Answer: For (1) what is the volume of tea when you poor away 2/3 of the drink? (it is 33.3cm3). OK so you add in a sugar cube.

For (2) volume no change. But you add in 3 sugar cubes and so remember that good old water distributes the sugar nicely, so divide the volume 100cm3 into 3, and 33.3cm3 gets an added sweetness of 1 sugar cube.

the formula for concentration is mol/dm3 means that AMOUNT OF STUFF divide by VOLUME OF SOVLENT.

Right? One thing to note is sweetness is just like concentration… the sweeter something is, the more concentrated the amount of sugar is in the thing.

Now, it is easily to wonder what exactly a solution is…

and so a solution is just plain water with DISSOLVED SUBSTANCES.

a solution like the tea just now contains LOTS AND LOTS of water, and a bit of STUFF FROM TEA LEAVES and a bit of SUGAR.

the key thing is that there is lots and lots and lots of water.

To make Coca Cola, you may use a big vat of 1000 litres of plain water.

then you add in about 100g of flavouring, and 200g of other kind of things, and 100g of some acid… and that makes Coke taste like Coke.

So it is a solution, but it is still just LOTS AND LOTS of water.

there are many different solutions out there, like the blue copper (II) sulphate solution, sodium hydroxide, HCL, etc, but they are all called solutions because WATER is really present all time in LARGE QUANTITIES.

 

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