Part 3 of Solution Chemistry Background Lab

Part 3 of Solution Chemistry Background Lab - PPT

Dilution from a Stock Solution. 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. ”.. ID: 536161

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Part 3 of Solution Chemistry Background Lab

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Part 3 of Solution Chemistry Background Lab
Dilution from a Stock Solution
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)
V =
1 L
n = 2 fish
Concentration =
# of fish
volume (L)
Concentration =
2 fish
1
L
Concentration =
V =
1 L
n = 2 fish
Concentration = 2 “fishar”
= 2 “
fishar”
Concentration =
4
fish
1
L
Concentration =
V =
1 L
n = 2 fish
Concentration
= 2 “
fishar
”
V =
1 L
n = 4 fish
[ ] = 4 “fishar”
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”
Now let’s do the same thing with moles.
We are going to use a concentration unit of
moles in
water called
“molar”.
V =
1 L
n = 2 moles
Concentration = 2 molar
Concentration =
2
moles
1
L
V =
1 L
n = 2 moles
Concentration = 2 molar
V =
1 L
n = 4 moles
[ ] = 4 molar
Concentration =
4
moles
1
L
0
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
1
Molarity
Molarity is the number of moles of solute dissolved per liter of solution.Perform problems 1 to 2 on your lab sheet.
2
Making Dilute Solutions
…from
stock solutions
3
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.
Concentration
4
Making a Dilute Solution from a Stock Solution
concentrated
stock solution
5
Making a Dilute Solution
concentrated
stock solution
moles of
solute
remove small
sample of stock solution
6
Making a Dilute Solution
concentrated
stock solution
add water and mix
remove small
sample of stock solution
moles of
solute
7
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
solute
8
Calculations
concentrated
stock solution
remove smallsample of stock solution
How do we calculate the number of moles of solute removed from the stock solution?
moles of
solute
9
Calculations
concentrated
stock solution
remove smallsample of stock solution
molarity =
so...
moles of solute = molarity of stock solution x volume of stock solution
moles of
solute
0
Calculations
concentrated
stock solution
remove smallsample of stock solution
moles of solute = molarity of stock solution x volume of stock solution
moles = M x V
moles of
solute
1
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 NaCl
NaCl
NaCl
NaCl
NaCl
2
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 NaCl
NaCl
NaCl
NaCl
NaCl
3
Practice problems 3 – 5 on your lab sheet now.
4
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
NaCl
5
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
NaCl
6
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 M
7
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.
molesconcentrate = molesdilute
8
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.
molesconcentrate = molesdiluteMcVc = MdVd
9
Dilution: McVc = 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?
0
Dilution: McVc = 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:
M
c
= 2.8 M
M
d
= 0.25 M
V
d
= 1.5 L
1
Dilution: McVc = 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:
M
c
= 2.8 M
M
d
= 0.25 M
V
d
= 1.5 L
Unknown:
V
c
= ?
2
Dilution: McVc = 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:
M
c
= 2.8 M
M
d
= 0.25 M
V
d
= 1.5 L
Unknown:
V
c
= ?
Equation:
M
c
V
c
=
M
d
V
d
3
Dilution: McVc = 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:
M
c
= 2.8 M
M
d
= 0.25 M
V
d
= 1.5 L
Unknown:
V
c
= ?
Equation:
M
c
V
c
=
M
d
V
d
Substitution:
(2.8M) x
V
c
= (0.25M)(1.5L)
4
Dilution: McVc = 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 LUnknown: Vc = ?Equation: McVc = MdVdSubstitution: (2.8M) x Vc = (0.25M)(1.5L)
5
Dilution: McVc = 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 LUnknown: Vc = ?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.
6
Dilution: McVc = MdVd
Now practice some dilution problems on your own. Do problems 6 – 7 on your lab sheet.
7
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
Notes
8
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
Notes
9
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
Notes
0
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
Notes
1
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
Notes
2
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
Notes
Can
be used for many different volumes
Can be used for many
different volumes
Can only be used for one specific volume
3
Glassware choices
Perform questions 8 through 10 now.
Device1000 mL beaker1000 mL graduated cylinder1000 mL volumetric flaskVolume1000 mL1000 mL1000 mLTolerance± 5%± 6 mL± 0.3 mLPossible volume range of measurement950 mL to 1050 ml994 mL to 1006 mL999.7 mL to 1000.3 mLCost$8.40$80.15$38.25NotesCan be used for many different volumesCan be used for many different volumesCan only be used for one specific volume
4