Transcript Making Dilutions from Solutions - Dr. Vernon-

Making Dilutions from Solutions
Think about what the word “dilute”
means. What must be added to make
a solution more dilute?
Making Dilutions
• It is very common to make a more dilute
solution by diluting a small amount of more
concentrated solution (called the stock
solution).
• Calculations to determine the amount of
concentrated solution needed are based on a
simple idea: the number of moles of a solute
does not change when a solution is diluted.
Therefore:
• M1V1 = M2V2
• Where
– M1 describes the molarity of the stock (more
concentrated) solution
– M2 and V2 describe the molarity and volume of
the more dilute solution you’re making
– V1 is unknown; it’s the amount of stock solution
you have to measure out and then dilute
Making a dilution is also a simple process:
1. Determine volume of concentrated solution
needed (calculate using M1V1 = M2V2) and
measure in a graduated cylinder or volumetric
pipet
2. Pour more concentrated solution into the
proper size volumetric flask
3. Add enough distilled water to make the
necessary amount of solution
4. Cover the volumetric flask and mix completely
by inverting
Example
• 0.10 M HCl is needed for a lab. How would 250
mL of 0.10 M HCl be prepared from 6.0 M HCl
stock solution?
Step 0.5 (before step 1 ) – identify your variables:
• M1 = concentration of stock solution = 6.0M
• V1 = volume of stock solution = unknown (what
we are solving for)
• M2 = goal concentration = 0.10M
• V2 = goal volume = 250 mL = 0.250 L
Example, continued
1. Solve for V1
• Original equation: M1V1 = M2V2
• Plug in numbers: 6.0M x V1 = 0.10M x 0.250L
• Solve for unknown: V1 = 0.0042 L = 4.2 mL of
concentrated stock solution required to make
final desired solution
Example, continued
2. Briefly describe the process of making the solution.
• Calculate the required amount of stock solution
(M1V1=M2V2).
• Measure out that much stock solution using a
graduated cylinder or volumetric pipet.
• Put stock solution in appropriate size volumetric flask.
• Add distilled water to reach desired final volume.
• Cover volumetric flask and mix completely by inverting.
Practice
• 0.2 M CuSO4 is needed for a lab. You have a stock
solution of 1.5 M CuSO4. How much stock
solution do you need to make 250 mL of the
desired solution? (first identify your variables!)
• M1 = 1.5 M
• V1 = ??
• M2 = 0.2 M
• V2 = 250 mL = 0.25 L
• 1.5 M x V1 = 0.2 M x 0.25 L
• V1 = 0.0333 L = 33.3 mL of 1.5 M CuSO4