TOPIC: Concentration and Dilution

Do Now:

Parts of a Solution

• Solute = dissolved substance

• Solvent = dispersing medium

We can determine how much solute and solvent make up a solution = CONCENTRATION

Concentration = A measurement that describes how much solute is in a given amount of solvent or solution.

Many, many different units to express concentration. • Molarity• PPM (parts per million)• % by mass• % by volume

Molarity (M)

Molarity (M) = moles of solute

liters of solution

CAN USE THIS TO HELP CALCULATE moles

M liters

So why do aqueous solutions need .1M or 3M

in front?!?!?!

VS

Dilution

-which one has a higher molarity?

Amount of solute is constant

Amount of solvent increases

Amount solute in concentrated solution

EQUALS

Amount solute in dilute solution

Dilution = add water = less concentrated

MolarityC x VolumeC = MolarityD x VolumeD

MC x VC = MD x VD

(C = concentrated D = dilute)

300ml of 2.5M NaOH is diluted to 750ml. Find the molarity of the diluted solution

MC x VC = MD x VD

300ml x 2.5M = 750ml x MD

300ml

2.5M 2.5M

?M

750ml

water

1M

So how much water did we have to add to delete the 2.5 M solution? 750

-300 _ 450ml

Example: We are doing a lab and the procedure calls for 300ml 1.2 M NaOH. However, all we have is a bottle of 5.5M NaOH.

We have to dilute it!!!!

The Equation: MC x VC = MD x VD

5.5 M x VC = 1.2 M x 300ml

V1 = (1.2 M x 300 ml) 5.5 M

So what does 65 ml tell us?!

V1 = 0.065 L = 65 mL

To prepare the 1.2 M NaOH solution, you pour 65 mL of 5.5 M NaOH into your container and add water to get 300 mL final volume (300-65 = 235 ml water added)