Dilutions and Percent Dilutions and Percent SolutionsSolutions

Unit 8 – SolutionsUnit 8 – Solutions

Chapter 15Chapter 15

Dilutions and MolarityDilutions and Molarity

Use this formula to make a more dilute Use this formula to make a more dilute solution from a concentrated solutionsolution from a concentrated solution

MolarityMolarity11VolumeVolume11 = Molarity = Molarity22VolumeVolume22

(Concentrated)(Concentrated) (Dilute)(Dilute)

(Moles before) = (Moles after!)(Moles before) = (Moles after!)

M1V1 = M2V2

Sample Problem #1Sample Problem #1How many milliliters of 1.0 Molar HCl are required How many milliliters of 1.0 Molar HCl are required

to make 100 mL of 0.025 M HCl?to make 100 mL of 0.025 M HCl?

MM11VV11 = M = M22VV22

MM11 = 1.0M V = 1.0M V11 = ? M = ? M22 = 0.025M V = 0.025M V22 = 100mls = 100mls

(1.0M)V(1.0M)V11 = (0.025M)(100mls) = (0.025M)(100mls)

VV11 = = (0.025M)(100mls)(0.025M)(100mls)

(1.0M)(1.0M)

= 2.5 mls of 1.0M HCl required, then dilute to 100mls= 2.5 mls of 1.0M HCl required, then dilute to 100mls

Sample Problem #2Sample Problem #2 How much How much waterwater should you add to the should you add to the

volume of 1.0M HCl you calculated above to volume of 1.0M HCl you calculated above to make the solution?make the solution?

We need 2.5 mls of concentrated 1.0M HCl. We need 2.5 mls of concentrated 1.0M HCl. Then we dilute to a final total volume of Then we dilute to a final total volume of

100mls.100mls.

Therefore, 100mls – 2.5mls = 97.5 mls of Therefore, 100mls – 2.5mls = 97.5 mls of water should be added.water should be added.

**Water added = V**Water added = V22 – V – V11

Percent SolutionsPercent Solutions Solutions can also be represented as percent of Solutions can also be represented as percent of

solute in a specific mass or volume of solvent.solute in a specific mass or volume of solvent.

For a solid dissolved in water, you use percent For a solid dissolved in water, you use percent by mass.by mass.

% by mass = mass solute x 100% by mass = mass solute x 100 mass of solutionmass of solution

*Mass of solution = solute mass + solvent mass*Mass of solution = solute mass + solvent mass

For a liquid mixed with another For a liquid mixed with another liquidliquid

% by volume = volume solute x 100% by volume = volume solute x 100

Total volume of solutionTotal volume of solution

Example 1Example 1What percent solution do you have if you What percent solution do you have if you

dissolve 80 grams of NaCl in 1 liter of dissolve 80 grams of NaCl in 1 liter of water?water?

* 1 Liter = 1000mls = 1000grams for water* 1 Liter = 1000mls = 1000grams for water

% mass = 80 grams NaCl X 100% mass = 80 grams NaCl X 100

(80g + 1000g H(80g + 1000g H22O)O)

= 7.4 %= 7.4 %

Example #2Example #2 What percent solution will you have if you What percent solution will you have if you

mix 40mls of ethanol with 200 mls of mix 40mls of ethanol with 200 mls of water?water?

%volume = 40mls x 100%volume = 40mls x 100

(200mls + 40mls)(200mls + 40mls)

= 16.7%= 16.7%

What if the previous problem was What if the previous problem was worded as follows?worded as follows?

What percent solution will you have if you What percent solution will you have if you dilutedilute 40mls of ethanol to a 40mls of ethanol to a final volumefinal volume of 200mls?of 200mls?

% volume = 40mls x 100% volume = 40mls x 100

200mls*200mls*

= 20%= 20%

*Denominator is always total volume. You must pay attention the wording in the problem!