Dilution from a Stock Solution Review What is meant by molarity Lets look at some examples To illustrate we are going to use a concentration unit of fish in water called fishar ID: 536161
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Slide1
Part 2 of Solution Chemistry Background Lab
Dilution from a Stock SolutionSlide2
Review
What is meant by “molarity?”
Let’s look at some examples.
To illustrate, we are going to use a concentration unit of fish in water called “fishar”.
Fishar
=
# of fish
volume (L)Slide3
V =
1 L
n = 2 fish
Concentration =
# of fish
volume (L)Slide4
Concentration =
2 fish
1
L
Concentration =
V =
1 L
n = 2 fish
Concentration
= 2 “
fishar
”
= 2 “
fishar
” Slide5
Concentration =
4
fish
1
L
Concentration =
V =
1 L
n = 2 fish
Concentration
= 2 “
fishar
”
V =
1 L
n = 4 fish
[ ] = 4 “fishar”Slide6
Concentration =
20 fish
5 L
Concentration =
V =
1 L
n = 2 fish
Concentration
= 2 “
fishar
”
V =
1 L
n = 4 fish
[ ] = 4 “fishar”
V =
5 L
n = 20 fish
[ ] = 4 “fishar”Slide7
Now let’s do the same thing with moles. We are going to use a concentration unit of
moles in
water called
“molar”.Slide8
V =
1 L
n = 2 moles
Concentration = 2 molar
Concentration =
2
moles
1
LSlide9
V =
1 L
n = 2 moles
Concentration = 2 molar
V =
1 L
n = 4 moles
[ ] = 4 molar
Concentration =
4
moles
1
L
Slide10
V =
1 L
n = 2 moles
Concentration = 2 molar
V =
1 L
n = 4 moles
[ ] = 4 molar
V =
5 L
n = 20 moles
[ ] = 4 molar
Concentration =
20
moles
5 L
Slide11
Molarity
Molarity is the number of moles of solute dissolved per liter of solution.
Perform problems 1 to 2 on your lab sheet.
Slide12
Making Dilute Solutions
…from
stock solutionsSlide13
Concentration
…a measure of solute-to-solvent ratio
concentrated
vs.
dilute “
lots of solute” “not much solute” “watery”
In order to dilute a concentrated solution, you add more water.
ConcentrationSlide14
Making a Dilute Solution from a Stock Solution
concentrated
stock solutionSlide15
Making a Dilute Solution
concentrated
stock solution
moles of
solute
remove small
sample of stock solutionSlide16
Making a Dilute Solution
concentrated
stock solution
add water and mix
remove small
sample of stock solution
moles of
soluteSlide17
Making a Dilute Solution
concentrated
stock solution
remove small
sample of stock solution
diluted solution
same number of
moles of solute
in a larger volume
add water and mix
moles of
soluteSlide18
Calculations
concentrated
stock solution
remove small
sample of stock solution
How do we calculate the number of moles of solute removed from the stock solution?
moles of
soluteSlide19
Calculations
concentrated
stock solution
remove small
sample of stock solution
molarity =
so...
moles of solute = molarity of stock solution x volume of stock solution
moles of
soluteSlide20
Calculations
concentrated
stock solution
remove small
sample of stock solution
moles of solute = molarity of stock solution x volume of stock solution
moles = M x V
moles of
soluteSlide21
Example
Ex: How many moles of
NaCl
would be contained in 0.50 L of a 4.0M
NaCl
stock solution?
Stock solution:
1.0 L of 4.0 M NaClNaCl
NaCl
NaCl
NaClSlide22
Calculations
Ex: How many moles of
NaCl
would be contained in 0.50 L of a 4.0M
NaCl
stock solution?moles = M x V = 4.0M x 0.50 L = 2.0 moles
NaCl
Stock solution:0.5 L of 4.0 M NaClNaCl
NaCl
NaCl
NaClSlide23
Practice problems 3 – 5 on your lab sheet now.Slide24
Dilution
In order to dilute the original solution, we can take the 0.5 L of the 4.0M stock solution and place it in another beaker and add water to bring the total volume back to 1.0 L
Stock solution:
0.5 L of 4.0 M
NaCl
NaCl
NaCl
NaCl
NaClSlide25
Dilution
NaCl
NaCl
In order to dilute the original solution, we can take the 0.5 L of the 4.0M stock solution and place it in another beaker and add water to bring the total volume back to 1.0 L
Stock solution:
0.5 L of 4.0 M
NaCl
NaCl
NaCl
NaCl
NaClSlide26
Dilution
NaCl
NaCl
Now the 2 moles are dissolved in 1 L of solution rather than 0.5 L of solution. They have been diluted. It’s the same number of moles, but in more water.
We can calculate the new molarity using the molarity equation.
M =
mol
/VM = 2 moles / 1.0 LM = 2 MSlide27
Dilution
NaCl
NaCl
An important point in dilution is that the moles of solute you use from the concentrated solution is the same as the moles in the new dilute solution that you make.
moles
concentrate
=
molesdiluteSlide28
Dilution
NaCl
NaCl
An important point in dilution is that the moles of solute you use from the concentrated solution is the same as the moles in the new dilute solution that you make.
moles
concentrate
=
molesdiluteMc
V
c
=
M
d
V
dSlide29
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Slide30
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Givens: Mc
= 2.8 M Md = 0.25 M Vd = 1.5 LSlide31
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Givens: Mc
= 2.8 M Md = 0.25 M Vd = 1.5 LUnknown: Vc
= ?Slide32
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Givens: Mc
= 2.8 M Md = 0.25 M Vd = 1.5 LUnknown: Vc
= ?
Equation:
M
c
V
c = MdVdSlide33
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Givens: Mc
= 2.8 M Md = 0.25 M Vd = 1.5 LUnknown: Vc
= ?
Equation:
M
c
V
c = MdVd
Substitution: (2.8M) x Vc = (0.25M)(1.5L)Slide34
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Givens: Solve:
Mc = 2.8 M Vc = 0.13L Md = 0.25 M = 130 mL Vd = 1.5 L
Unknown:
V
c
= ?
Equation:
McVc =
MdVdSubstitution: (2.8M) x Vc = (0.25M)(1.5L)Slide35
Dilution:
M
c
V
c
= MdVd
Let’s see how this equation works.Ex: You want to make 1.5 L of 0.25 M NaCl from a stock solution of NaCl that has a concentration of 2.8 M. What volume of the stock solution do you need to use to make your dilute solution?Givens: Solve:
Mc = 2.8 M Vc = 0.13L Md = 0.25 M = 130 mL Vd = 1.5 L
Unknown:
V
c
= ?
Equation:
McVc =
MdVdSubstitution: (2.8M) x Vc = (0.25M)(1.5L)
What this means is that to make your dilute solution, you will need to measure out 130 mL of the stock solution, add it to a 1.5 L volumetric flask, and then add water to the line to dilute it.Slide36
Dilution:
M
c
V
c
= MdVd
Now practice some dilution problems on your own. Do problems 6 – 7 on your lab sheet.Slide37
Glassware choices
Why do we use the volumetric flask instead of a beaker or graduated cylinder to make solutions?
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
Tolerance
Possible
volume range of measurement
Cost
NotesSlide38
Glassware choices
Why do we use the volumetric flask instead of a beaker or graduated cylinder to make solutions?
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
1000 mL
1000 mL
1000 mL
Tolerance
Possible
volume range of measurement
Cost
NotesSlide39
Glassware choices
Why do we use the volumetric flask instead of a beaker or graduated cylinder to make solutions?
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
1000 mL
1000 mL
1000 mL
Tolerance
±
5%
±
6
mL
±
0.3
mL
Possible
volume range of measurement
Cost
NotesSlide40
Glassware choices
Why do we use the volumetric flask instead of a beaker or graduated cylinder to make solutions?
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
1000 mL
1000 mL
1000 mL
Tolerance
±
5%
±
6
mL
±
0.3
mL
Possible
volume range of measurement
950 mL to 1050 ml
994 mL to 1006
mL
999.7
mL to 1000.3 mL
Cost
NotesSlide41
Glassware choices
Why do we use the volumetric flask instead of a beaker or graduated cylinder to make solutions?
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
1000 mL
1000 mL
1000 mL
Tolerance
±
5%
±
6
mL
±
0.3
mL
Possible
volume range of measurement
950 mL to 1050 ml
994 mL to 1006
mL
999.7
mL to 1000.3 mL
Cost
$8.40
$80.15$38.25
NotesSlide42
Glassware choices
Why do we use the volumetric flask instead of a beaker or graduated cylinder to make solutions?
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
1000 mL
1000 mL
1000 mL
Tolerance
±
5%
±
6
mL
±
0.3
mL
Possible
volume range of measurement
950 mL to 1050 ml
994 mL to 1006
mL
999.7
mL to 1000.3 mL
Cost
$8.40
$80.15$38.25
NotesCan be used for many different volumes
Can be used for many
different volumes
Can only be used for one specific volumeSlide43
Glassware choices
Perform questions 8 through 10 now.
Device
1000
mL beaker
1000
mL graduated cylinder
1000 mL volumetric flask
Volume
1000 mL
1000 mL
1000 mL
Tolerance
±
5%
±
6
mL
±
0.3
mL
Possible
volume range of measurement
950 mL to 1050 ml
994 mL to 1006
mL
999.7
mL to 1000.3 mL
Cost
$8.40
$80.15$38.25
NotesCan be used for many different volumesCan be used for many different volumes
Can only be used for one specific volume