Volumetric

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A solution is prepared by dissolving a solute in a solvent.

Slide 17

When a solution is diluted, more solvent is added to it, the number of moles of solute stays the same.

i.e. n1 = n2

Recall, C = n ÷ V,

Make n the subject and substitute, it follows that

C1V1 = C2V2

where C1=original concentration of solution

V1=original volume of solution

C2=new concentration of solution after dilution

V2=new volume of solution after dilution

n1 = no of mol of solute before dilution

n2 = no of mole of solute after dilution

Slide 18

To calculate the new concentration (C2) of a solution given its new volume (V2) and its original concentration (C1) and original volume (V1).

Note: V2 = V1 + vol. of water added.

Slide 19

Examples

Calculate the new concentration (molarity) if enough water is added to 100cm3 of 0.25M sodium chloride to make up 1.5dm3.

C2=(C1V1) ÷ V2

C1 = 0.25M

V1 = 100cm3 = 100 ÷ 1000 = 0.100dm3 (volume must be in dm3)

V2 = 1.5dm3

[NaCl(aq)]new = C2 = (0.25 x 0.100) ÷ 1.5 = 0.017M

(or 0.0.017 mol/dm3)

Slide 20

More

If 280cm3 of a 3moldm-3 sodium hydroxide solution is diluted to give 0.7moldm-3 soln.

What is the vol. of the resulting diluted solution?

What is the vol. of distilled water added to the original soln.?

Slide 21

Let’s do it

V1 = 280cm3 ,C1 = 3moldm-3 ,C2 = 0.7moldm-3

V2 = ?

C1V1 = C2V2

V2 = 3 X 280 = 1200cm3 0.7

To know the vol. of distill water added

V2 = V1 + vol. of distill water added.

vol. of distill water added.= 1200 – 280

= 920cm3

Slide 22

One more!

Calculate the vol. of a 12.0moldm-3 HCl that should be diluted with distilled water to obtain 1.0dm3 of a 0.05moldm-3 HCl.

Soln.

C1 = 12moldm-3, V1 = ?

C2 = 0.05moldm-3 , V2 = 1.0dm3

I’ve done my own part, do yours!

Slide 23

PRActice problems

Slide 24

Acid-Base Titrations

Acid-base titrations are lab procedures used to determine the concentration of a solution. We will examine it's use in determining the concentration of acid and base solutions.

Titrations are important analytical tools in chemistry.

Slide 25

During the titration