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Part 3 of Solution Chemistry Background Lab Part 3 of Solution Chemistry Background Lab

Part 3 of Solution Chemistry Background Lab - PowerPoint Presentation

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Part 3 of Solution Chemistry Background Lab - PPT Presentation

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

nacl solution 1000 stock solution nacl stock 1000 moles volume concentration dilute dilution solute volumetric beaker flask fish graduated

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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