GIVING DIRECTIONS && DILUTION OF SOLUTIONS

Dec.2/09

In class today, we went over the homework to Molar Concentration (see post before this). But there was one question that not many people understood, which was #26 on the homework sheet, (the one about giving a procedure).

This section is called GIVING DIRECTIONS.
This procedure is to find out what mass you need in order to complete the solution.

Example:
George is asked to make a 0.66 M solution of K2SO4. If he needs 301 ml, what procedure should he use?

So your formula is : C = n/v
And you want to go from CONCENTRATION > MOLES > MASS

0.66 mol/L x 174.3 G/mol x 1 L/1000 ml x 301 ml/1 = 28.8 G

So with this equation you have just developed, you need to write the steps:

1) Measure 301 ml of water
2) Weight 28.8 g of K2S04
3) Add 28.8 g of K2S04 to the water, and stir until dissolved.

MAKE SENSE GUYS? :)

We then proceeded to DILUTION OF SOLUTION.
This means that when you add water to a solution, the concentration of it decreases.
But this also means, that if the volume is doubled, the concentration of it is halved.

Let's take a look at this chart that proves this:

As you can see in this chart, the number of moles do not change, and as you move down the volume section, six is multiplied twice, then by four times to get 48.. And as you are doing this, the concentration section is going the opposite, going down by half then by one fourth, this is called an inverse relationship.

Our formula for this section is C1V1=C2V2

Let's do an example:

Carolyn and Sheryl add 200 ml of water to 55 ml of 0.75 M HCl. Find [HCl] (concentration).

You first need to write down what you know, and what you don't.

V1 = 55 ml

V2 = 255 ml

C1 = 0.75 M

C2 = ?

You then use the equation (C1V1=C2V2), and fill in what you know. You will find that the C2 part is left as C2 -> treat it as a variable, like x, and solve for it!

Your answer should be: 0.16 M.

So uhhh.. YEAH, that's all for today's lesson guys.. Hope you get it ;)

(Queen's Post)