Concentration/Dilution

Solution Preparation

•Preparing a solution of Sodium Chloride (NaCl)

•Solute= Sodium Chloride (solid)

•Solvent = water (distilled)

•We know that we define solutions based on CONCENTRATION (Molarity)

•Molarity (M) - the number of moles of solute dissolved in a certain volume of the total solution. (mol/L)

Solution Preparation

• Preparing Solution

• preparing a 500ml of a 0.25mol of NaCl solution

• need to calculate how many grams of NaCl we need for the solution

0.25mol = 0.25 mol/L

500mL x 1 L 1000mL

= 0.500L

0.500L x 0.25 mol1 L

=0.125 mol NaCl

0.125 mol x 58.43g1 mol

= 7.304g of NaCl

In Lab you need these materials

•sodium chloride

•scoop

•scale

•glass stir rod

•distilled water

•volumetric flask

•Making Up a Standard Solution

•http://www.youtube.com/watch?v=cckAwavEKA0

Prepare a 250mL of a 0.500mol/L solution of Sodium Chloride

•Step #1: Determine the mass of Sodium Chloride required

Prepare a 250mL of a 0.500mol/L solution of Sodium Chloride

•Step 2: place the amount in a 250mL volumetric flask. If difficult add the amount to a beaker.

•Step 3: Distilled water is added until the flak is about half full.

•Step 4: The flask is shaken until the solid has completely dissolved

•Step 5: Distilled water is again added until the flask is full to the mark.

Calculating the Percent

Concentration.• Volume Percentage (% V/V)

• Used for solutions of a liquid in a liquid

• Volume % of solute = Volume of solute

• Examples:

• Percentage of acetic acid in vinegar

• Percentage of alcohol in beer and spirits

volume of solutionx 100%

Calculating the Percent

Concentration.•Mass Percentage (% m/m)

•Used for solid solutions --> alloys

•Mass % of solute = mass of solute

•Examples:

•Percentage of copper in brass

• Iron in stainless steel or silver

mass of solute & solventx 100%

Calculating the Percent

Concentration.• Weight volume Percentage (% m/v)

• Usually used in household products when a mass of a solute is dissolved in the solvent which is a liquid.

• Mass volume % = weight of solute(g)

• Examples:

• Percentage of caffeine in a cup of tea

volume of solvent (mL)x 100%

Dilution

•Dilution: increasing the amount of solvent and the concentration decreases.

•common way to take a stock solution & create other solutions.

• c = n V

remains constant

increases (b/c water is added)decreases

(b/c volume increases)

Dilution

•During a dilution, the concentration of a solution decreases due to an increase of its volume. The amount of solute remains unchanged

Dilution Equation

CiVi = CfVf

Dilution•Calculate the volume of a

0.10M solution made from 200mL of 0.30M NiCl2CiVi = CfVf

Dilution

•Calculate the volume of a 0.10M solution made from 200mL of 0.30M NiCl2

CiVi = CfVf

Add 400mL of water ---to finally end up with 600mL Solution