UNIT V: lesson 6Molar Concentration & Dilutions

CONCENTRATION

Concentration of a substance in a solution is the amount of this substance that exists in in a volume of solution.

A concentrated solution: has a relatively high concentration (There is a large amount of the substance dissolved in the solution)

A dilute solution: has a relatively low concentration ( very little substance is dissolved in the solution).

MOLAR CONCENTRATIONS

Chemists like to use ‘mole’ to describe amount of substance in solutions.

Molar Concentration or Molarity (M) is the number of moles (n) of the substance in 1 L of solution.

Units for Molarity

A short hand symbol for Molar Concentration is

MOLAR CONCENTRATION Ex: what is the molar concentration of 1 L of

solution containing 2.5 mol of NaCl?

Ex: what is the [NaCl] in a solution containing 5.12 g of NaCl in 250 mL of solution?

What mass of NaOH is contained in 4 L of 0.2 M NaOH?

What is the molariy of H2SO4 having a density of 1.839 g/mL?

DILUTION CALCULATIONS

What happens when you mix two solutions together?!

Mixing two solutions together will dilute the original solutions.

This means, there will be new concentrations and new volumes

DILUTION CALCULATIONS

Molarity/Concentration = moles(n) Volume (L)

Molarity of Mixture = Total moles (n) Total volume of mixture (L)

 

DILUTION CALCULATIONS

*Consider a concentrated solution that we add water to in order to make a diluted solution.  CI = initial concentration of solution

VI= initial volume of solution

After we add water….

 CDIL = diluted concentration (after water is added)VDIL = (total) diluted volume (after water is added)

DILUTION CALCULATIONS

Recall that c = n/V... therefore n= c·V

 nI = moles for Initial solutions

= CI x VI

nDIL = moles in DIL solution

= CDIL x VDIL

The Total number of moles (n) for each solution that we started with does not change when we mix the two solutions together….it stays the same.

DILUTION CALCULATIONS

nI = nDIL

CI x VI = CDIL x VDIL

or...

CIVI = CFVF

A. Simple Dilution of a Chemical in Solution Example #1: If 400.0 mL of 0.800M HCl is added to 500.0 mL of water, what is the resulting [HCl] in the mixture?

B. Mixing 2 Solutions with Different ConcentrationsTreat mixtures of two solutions as two

separate “single dilutions”Example #2: If 300.0 mL of 0.350 M H2SO4 is added to 400.0 mL of 0.050 M H2SO4, what is the resulting [H2SO4] in the mixture?

C. Making a Dilute Solution from a Concentrated SolutionExample #3: What volume of 8.00 M H2O2 is used in making up 1.5 L of 0.5 M H2O2?

TRY:Miss Q. mixes 200mL of water with 50 mL of a sodium chloride solution having an unknown concentration. Miss Q. finds that the molarity of the sodium chloride after dilution was 0.0864 M.

What was the molarity of the original sodium chloride solution??

SUMMARY OF DILUTION CALCULATIONS

Always, always, always use

Remember for final volume (VF) to add up the two volumes together. It is a total volume.

Be careful when you are substituting the numbers in the equation.

SUMMARY OF DILUTION CALCULATIONS

Always, always, always use

To find new concentration, simply rearrange into

[New concentration] = [old concentration] x old volume

total volume

REMEMBER…

Molarity is the same as molar concentration.

It is in moles/L If you have units in moles/mL, must change it

into moles/L first.

Ex: 500 mL L Divide by 1000 = 0.5 L

If you have units in grams, change g moles by using the molar mass!

TRYSuppose you have 5.60g of KCl and you wanted to make a 2.14 M solution. What volume of solutionwould you create?

HOMEWORK

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