Molarity Dilution.ppt

Molarity problems

1. Molarity & Dilution
Aleigha Benoit
Chemistry 12
December 15th

2. Helpful Definitions
•Solutions: homogeneous mixture of two or more
substances physically mixed together in a uniform way.
•Solute:substance being dissolved.
•Solvent:part of a solution doing the dissolving.
•Soluble:when a substance dissolves in another
substance.
•Solubility:the ability of a substance to dissolve in
another substance.
•Dilute:more solvent than solute in a solution.

3. Molarity
•Molarity (also called concentration) is a measure of the amount of solute
that is dissolved in a given amount of solution.
•Molarity is the number of moles of solute dissolved in one litre of solution.
Therefore, the equation to find the molarity (M) of a solution is :
M= n/v = moles of solute / litres of solution. The units are moles per litre.
•The simplified version for the equation M=n/v is M=g/mm x L, g
meaning grams, mm meaning the molar mass of the solution, and L
meaning litres.
•Be careful not to get molarity and moles mixed up. Molesmeasures the
amount of material you have. Molarity measures the concentration of the
material.

4. Molarity Example #1
Reminder: To make the question easier to work with, convert any unit of
mass to grams and any unit of volume to litres.
1. Calculate the molarity of a 5L solution containing 126g of
HNO3.
• Calculate the number of moles: 126g HNO3
=2 moles
• M= moles of solute
liters of solution
• M= 2mol HNO3
5L
• M= 0.4 mol/L

5. Molarity Example #2
Calculate the mass of NaOH needed to prepare 1.0L of a 1.5M solution.
( To do this, rearrange the equation M= g/mm x L to g= mm x m x L.)
What we need to find out: ___g?
What we know: Molar Mass (mm)= 40g/mol
Molarity : 1.5M
Liters: 1L
Plug these values into the equation : g= mm x m x L
g= (40g/mol)(1.5mol/L)(1L)
g= 60g

6. Molarity Example #3
960g of NaOH is used in preparing a 1.5M solution. What volume of
solution can be made?
(Rearrange M=g/mm x L to L= g/mm x m)
What we need to find out: ___L?
What we know: g= 960
mm= 40g/mol (Periodic Table)
M= 1.5mol/L
Plug these values into the equation: L= g/mm x m
L= (960g)(40g/mol)(1.5mol/L)
L= 16L

7. Dilution
Dilution is the process of decreasing the concentration of a stock solution by
adding more solvent to the solution. The solvent added is usually the
universal solvent, known as water. The more solvent you add, the more
diluted the solution will get.
A stock solution is a concentrated solution that will be diluted to a lower
concentration for actual use.
The equation for dilution is M1V1=M2V2
stock solution= diluted solution
•M1= molarity of the stock solution
•M2= molarity of the diluted solution
•V1= volume of stock solution
•V2= volume of diluted solution

8. The Dilution Equation
The equation for dilution is M1V1=M2V2
stock solution= diluted solution
•M1= molarity of the stock solution
•M2= molarity of the diluted solution
•V1= volume of stock solution
•V2= volume of diluted solution
Basically, dilution calculations involve figuring out the final concentration
or volume ( depending on what’s given and what’s known) after a
volume or concentration has been changed.
In dilution equations, you are given three things and you need to find the
forth component.

9. Dilution Example #1
A stock solution of 1.00M of NaCl is available. How many milliliters are needed to
make a 100.0 mL of 0.750M?
What we know: the molarity of the stock solution which is 1.00M, and the two
components of the diluted solution which are M2= 0.750M and
V2= 100 mL.
Plug in the values you have into the equation to solve for the missing value.
M1V1=M2V2

10. Dilution Example #2
Concentrated HCl is 12M. What volume is needed to make 2L of a 1M
solution?
What we know: the molarity of the stock solution which is 12M, and the
two values for the diluted solution which are M2=1M and
V2=2L.
Plug in the values you have into the equation to solve for the missing value.
M1V1=M2V2

11. Dilution Example #3
Calculate the final concentration if 2L of 3M of NaCl and 4L of 1.50M of
NaCl are mixed. Assume there is no volume contraction upon mixing.
For this, you must use the equation M= total mol/ total volume. So you
must find the total number of moles to do this calculation.

12. Works Cited
http://en.wikipedia.org/wiki/Molar_concentration
http://dl.clackamas.edu/ch105-04/molarity.htm
http://en.wikipedia.org/wiki/Stock_dilution
http://dl.clackamas.edu/ch105-04/dilution.htm
http://chemistry.about.com/od/lecturenotesl3/a/concentration.htm