Standard Solutions in Chemistry
Lecture 2.
Preparation of Standard solutions and
expression of results
By: Dinaol
1
4/28/2020
In this Lecture
Definitions of some terms
Definitions of standard solutions
Why we need to prepare standard solutions
Methods of Preparing standard solutions (Some calculations)
How to express the results of our test
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Definitions of related terms
Solutions
Homogeneous mixtures that are mixed so thoroughly that neither component
can be observed independently of the other.
Homogeneous mixture composed of two or more substances. In such a
mixture, a solute is dissolved in another substance, known as a solvent.
Solvent
The major component of solutions.
The substance which dissolves another to form a solution
Solute
The minor component of a solutions
The substance which dissolves in a solution
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Definitions of related terms …
Saturation
Saturation is the point at which a solution of a substance can
dissolve no more of that substance and additional amounts of it
will appear as a precipitate.
Supersaturation
It refers to a solution that contains more of the dissolved material
than could be dissolved by the solvent under normal
circumstances.
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Definitions of related terms …
Stock solutions
A stock solution is a concentrated solution that will be diluted to
some lower concentration for actual use.
Stock solutions are used to save preparation time, conserve
materials, reduce storage space, and improve the accuracy with
which working lower concentration solutions are prepared.
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Definition of Standard Solutions
What is Standard Solutions?
A standard solution is any chemical solution which has a precisely
known concentration. Similarly, a solution of known concentration
has been standardized.
To prepare a standard solution, a known mass of solute is dissolved
and the solution is diluted to a precise volume.
Standard solution concentration is usually expressed in terms of
molarity (M) or moles per liter (mol/L).
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Why we need to prepare Standard Solutions?
You use a standard solution to determine the concentration of the
analyte during laboratory tests.
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What must be considered during preparation
of standard solution?
The nature of solute
Must be pure (analytical grade)
Example, Oxalic acid , K2Cr2O7
The quality we need/expect at the end
Not all substances are suitable solutes for standard solutions.
The reagent must be stable, pure, and preferably of high molecular weight.
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Solutions recipes:
Where do they come from?
Original Scientific Literature
Lab manuals (instructional)
Lab Manuals (professional)
Handbooks
Manufacturers and suppliers
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Concentration Versus Amount
CONCENTRATION
-- amount / volume
•
Fraction
where:
•
Numerator, the amount of solute
•
Denominator, usually volume of entire solution
•
solvent + solute(s)
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Each star represents 1 mg of NaCl.
What is the total
amount
of
NaCl in the tube? _____
What is the
concentration
of NaCl in
the tube (in mg/mL)? _____
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Each star represents 1 mg of NaCl.
What is the total amount
of NaCl in the tube?
4 mg
What is the concentration
of NaCl in the tube (in mg/mL)?
4 mg
=
?_
5 mL 1 mL
? = 0.8 mg,so the
concentration is
0.8 mg/mL
Figure 1.
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Ways To Express Concentration Of Solute
•
Source of confusion:
more than one way to express concentration of
solute in a solution
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Concentration Expressions (Most Common)
•
WEIGHT PER VOLUME
•
MOLARITY
•
PERCENTS (Three kinds)
a. Weight per Volume % (w/v %)
b. Volume per Volume % (v/v %)
c. Weight per Weight % (w/w %)
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P
e
r
c
e
n
t
s
X % is a fraction
numerator is X
denominator is 100
Three variations on this theme.
15
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W
e
i
g
h
t
/
v
o
l
u
m
e
%
TYPE I:
•
Grams of solute
•
100 mL total solution
•
Most common in biology but seldom used in
chemistry manuals
•
Technically, the units should be the same in the
numerator and denominator
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Example
20 g of NaCl in
100 mL of total solution
= 20% (w/v) solution.
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Example:
By Proportions
•
How would you prepare 500 mL of a 5 % (w/v) solution of NaCl?
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Answer, By
Proportions
By definition:
5 % =
5 g
100 mL
5 g
=
?
100 mL 500 mL
? = 25 g = amount of solute
BTV 500 mL
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By Equation
How would you prepare 500 mL of a 5 % (w/v) solution of NaCl?
1.
Total volume required is 500 mL.
2.
5% = 0.05
3.
(0.05) (500 mL) = 25
4.
25 is the amount of solute required in grams.
5.
Weigh out 25 g of NaCl. Dissolve it in less than 500 mL of water.
6.
In a graduated cylinder or volumetric flask, bring the solution to 500 mL.
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Concentration Expressions (Most Common)
•
PARTS
(Common in environmental sciences, for example)
Amounts of solutes expressed as "parts"
a. Parts per Million (ppm)
b. Parts per Billion (ppb)
c. Might see parts per Thousand (ppt)
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Parts
•
Parts may have any units but must be the same for all components of
the mixture.
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Example:
A solution is 3:2:1 ethylene:chloroform:isoamyl alcohol
Might combine:
3 liters ethylene
2 liters chloroform
1 liter isoamyl alcohol
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Two Other Forms Of %
v/v
mL solute
100 mL solution
w/w
g solute
100 g solution
25
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Weight/weight
•
How would you make 500 g of a 5% solution of NaCl by weight (w/w)?
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Answer
•
Percent strength is 5% w/w, total weight desired is 500g.
•
5% = 5g/100g
•
5g
X 500 g = 25 g = NaCl needed
100 g
•
500 g – 25 g = 475 g = amount of solvent needed
•
Dissolve 25 g of NaCl in 475 g of water.
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Weight / Volume
Means a fraction with:
weight of solute in numerator
total volume in denominator
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Example:
•
2 mg/mL proteinase K
•
Means 2 mg of proteinase K in each mL of
solution.
•
Example: How much proteinase K is required
to make 50 mL of solution at a concentration
of 2 mg/mL?
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Can Solve as A
Proportion Problem
2 mg proteinase K =
X
1 mL solution 50 mL solution
X = 100 mg
= amount proteinase K needed.
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Volume / Volume
Means a fraction with:
volume of solute in numerator
total volume in denominator
•
Usually the “solute” here is a liquid as well
•
Remember that volume in the denominator is the total volume of
the solution
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Example
•
You are to make 50 mL of a 8% v/v solution of diluted dish soap.
•
How many mLs of concentrated dish soap must be added to how
many mLs of water?
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Weight / Weight
Means a fraction with:
mass of solute in numerator
total mass in denominator
•
Most times the “solute” here is a solid and sometimes the “solution”
is also a solid
•
Remember that mass in the denominator is the total mass of the
solution
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Examples
•
You are to prepare 4 kg of specific soil sample which is to be 8% w/w
sand and 5% w/w clay in which the remainder is top soil.
•
How many grams of each sand and clay need to be added to the soil
to make the solution?
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Ppm And Ppb
•
ppm:
The number of parts of solute per 1 million parts of total
solution.
•
ppb:
The number of parts of solute per billion parts of solution.
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Ppm Example:
•
5 ppm chlorine = 5 g of chlorine in 1 million g of solution,
•
or 5 mg chlorine in 1 million mg of solution,
•
or 5 pounds of chlorine in 1 million pounds of solution
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Conversions
To convert ppm or ppb to simple weight per
volume expressions:
5 ppm chlorine
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Conversions
To convert ppm or ppb to simple weight per
volume expressions:
5 ppm chlorine =
5 g chlorine
=
5 g chlorine
10
6
g water 10
6
mL water
=
5 mg/1 L water
= 5 X 10
-6
g chlorine/ 1 mL water
=
5 micrograms/mL
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PPM To
Micrograms/ml
For any solute:
1 ppm in water =
1 microgram
mL
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Each star represents 1 mg of dioxin.
What is the concentration of dioxin in the
beaker expressed as ppm (parts per million)?
____________
What is the total amount of
dioxin in beaker?
___________
40
4/28/2020
Each star represents 1 mg of dioxin.
What is the total amount of dioxin in tube?
25 mg
What is the concentration of dioxin in tube
expressed as ppm? ____________
1 ppm in water =
1
μ
g
mL
25 mg/500 mL
= 0.05 mg/mL= 50 μg/mL
so the concentration is 50 ppm
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Still More Concentration Expressions
TYPES NOT COMMON IN BIOLOGY MANUALS:
•
MOLALITY
•
NORMALITY
1.
We remember that for NaOH and HCl, molarity = normality,
however, this is not true for all solutes
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More with Molarity
•
Molarity
is: number of moles of a solute that
are dissolved per liter of total solution.
•
By definition: A 1 M solution contains 1
mole of solute per liter total volume.
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M
o
l
e
•
How much is a mole?
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Examples:
Water, Sulfuric Acid and Glucose
For a particular compound, add the atomic
weights of the atoms that compose the
compound.
What is the formula weight for water H
2
O?
What is the formula weight for sulfuric acid
H
2
SO
4
?
What is the formula weight for glucose
C
6
H
12
O
6
?
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Example:
Sulfuric Acid
For a particular compound, add the atomic
weights of the atoms that compose the
compound.
H
2
SO
4
:
2 hydrogen atoms 2 X 1.00 g = 2.00 g
1 sulfur atom 1 X 32.06 g = 32.06 g
4 oxygen atoms 4 X 16.00 g =
64.00 g
98.06 g/mole
Glucose = 180 g/mole
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Example
Continued
•
A 1M solution of sulfuric acid contains 98.06 g of sulfuric acid in 1 liter
of total solution.
•
Observe that "mole" is an expression of
amount
•
“Molarity" is an expression of
concentration
.
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Definitions
•
"Millimolar", mM, millimole/L.
•
A millimole is 1/1000 of a mole.
•
"Micromolar", µM, µmole/L.
•
A µmole is 1/1,000,000 of a mole.
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Formula
HOW MUCH SOLUTE IS NEEDED FOR A
SOLUTION OF A PARTICULAR MOLARITY AND
VOLUME?
FW X molarity x volume = g solute
needed
49
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Example
•
How much solute is required to make 300 mL of 0.8 M CaCl
2
?
50
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Answer
Substituting into the formula:
(
111.0 g
) (
0.8 mole
) (0.3 L) = 26.64 g
mole
L
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Example
•
What is the concentration (M) of a salt solution that has 28 g of NaCl
in 185 mL of water?
•
What is the w/v% of this solution?
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To Make Solution
Of Given Molarity And Volume:
•
Find the FW of the solute, usually from label.
•
Determine the molarity desired.
•
Determine the volume desired.
•
Determine how much solute is necessary by using the formula.
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Procedure Cont.
•
Weigh out the amount of solute.
•
Dissolve the solute in less than the desired final volume of solvent.
•
Place the solution in a volumetric flask or graduated cylinder. Add
solvent until exactly the required volume is reached, “Bring To
Volume”, “BTV”.
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F
r
o
m
B
a
s
i
c
L
a
b
o
r
a
t
o
r
y
M
e
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o
r
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:
T
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o
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,
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0
0
0
56
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Preparing
Dilute Solutions
From Concentrated Ones
•
Concentrated solution = stock solution
•
Use this equation to decide how much stock
solution you will need: C
1
V
1
=C
2
V
2
•
C
1
= concentration of stock solution
•
C
2
= concentration you want your dilute
solution to be
•
V
1
= how much stock solution you will
need
•
V
2
= how much of the dilute solution you
want to make
57
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Example
•
How would you prepare 1000 mL of a 1 M
solution of Tris buffer from a 3 M stock of Tris
buffer?
•
The concentrated solution is 3 M, and is C
1
.
•
The volume of stock needed is unknown, ?, and is
V
1
.
58
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E
x
a
m
p
l
e
C
o
n
t
…
The final concentration required is
1 M, and is C
2
.
The final volume required is 1000 mL and is
V
2
.
59
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Substituting Into
The Equation:
C
1
V
1
= C
2
V
2
3 M (?) 1 M (1000 mL)
? = 333.33 mL
So, take 333.33 mL of the concentrated stock solution and BTV 1 L.
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“X” Solutions
•
The concentration of a stock solution is sometimes written with an
“X”.
•
The “X” is how many more times the stock is than normal.
•
You generally want to dilute such a stock to 1X, unless told otherwise.
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Example
•
A can of frozen orange juice is labeled 4X. How would you dilute it to
make 1L of drinkable drinkable juice?
•
Using the C
1
V
1
=C
2
V
2
equation:
C
1
V
1
= C
2
V
2
4X (?) = 1X (1L)
? = 0.25 L
Use 0.25 L of orange juice, BTV 1L.
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Biological Buffers
•
Laboratory buffers
solutions to help maintain a biological system at proper pH
•
pKa of a buffer
the pH at which the buffer experiences little change in pH with
addition of acids or bases = the pH at which the buffer is most useful
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Temperature
•
Some buffers change pH as their temperature and/or concentration
changes
•
Tris buffer, widely used in molecular biology, is very sensitive to
temperature
64
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Dilution
•
Some buffers are sensitive to dilution
•
Phosphate buffer is sensitive to dilution
65
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Definitions of terms like solute, solvent, and saturation are explained. The importance of preparing standard solutions, methods for their preparation, and how results are expressed are discussed. Stock solutions and their benefits are also covered. Images are used for illustration throughout the content.
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Presentation Transcript
Lecture 2. Preparation of Standard solutions and expression of results By: Dinaol 4/28/2020 1
In this Lecture Definitions of some terms Definitions of standard solutions Why we need to prepare standard solutions Methods of Preparing standard solutions (Some calculations) How to express the results of our test 4/28/2020 2
Definitions of related terms Solutions Homogeneous mixtures that are mixed so thoroughly that neither component can be observed independently of the other. Homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. Solvent The major component of solutions. The substance which dissolves another to form a solution Solute The minor component of a solutions The substance which dissolves in a solution 4/28/2020 3
Definitions of related terms Saturation Saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of it will appear as a precipitate. Supersaturation It refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. 4/28/2020 4
Definitions of related terms Stock solutions A stock solution is a concentrated solution that will be diluted to some lower concentration for actual use. Stock solutions are used to save preparation time, conserve materials, reduce storage space, and improve the accuracy with which working lower concentration solutions are prepared. 4/28/2020 5
Definition of Standard Solutions What is Standard Solutions? A standard solution is any chemical solution which has a precisely known concentration. Similarly, a solution of known concentration has been standardized. To prepare a standard solution, a known mass of solute is dissolved and the solution is diluted to a precise volume. Standard solution concentration is usually expressed in terms of molarity (M) or moles per liter (mol/L). 4/28/2020 6
Why we need to prepare Standard Solutions? You use a standard solution to determine the concentration of the analyte during laboratory tests. 4/28/2020 7
What must be considered during preparation of standard solution? The nature of solute Must be pure (analytical grade) Example, Oxalic acid , K2Cr2O7 The quality we need/expect at the end Not all substances are suitable solutes for standard solutions. The reagent must be stable, pure, and preferably of high molecular weight. 4/28/2020 8
Solutions recipes: Where do they come from? Original Scientific Literature Lab manuals (instructional) Lab Manuals (professional) Handbooks Manufacturers and suppliers 4/28/2020 9
Concentration Versus Amount CONCENTRATION -- amount / volume Fraction where: Numerator, the amount of solute Denominator, usually volume of entire solution solvent + solute(s) 4/28/2020 10
Each star represents 1 mg of NaCl. What is the total amount of NaCl in the tube? _____ What is the concentration of NaCl in the tube (in mg/mL)? _____ 4/28/2020 11
Each star represents 1 mg of NaCl. What is the total amount of NaCl in the tube? 4 mg What is the concentration of NaCl in the tube (in mg/mL)? 4 mg = ?_ 5 mL 1 mL ? = 0.8 mg,so the concentration is 0.8 mg/mL Figure 1. 4/28/2020 12
Ways To Express Concentration Of Solute Source of confusion: more than one way to express concentration of solute in a solution 4/28/2020 13
Concentration Expressions (Most Common) WEIGHT PER VOLUME MOLARITY PERCENTS (Three kinds) a. Weight per Volume % (w/v %) b. Volume per Volume % (v/v %) c. Weight per Weight % (w/w %) 4/28/2020 14
Percents Percents X % is a fraction numerator is X denominator is 100 Three variations on this theme. 4/28/2020 15
Weight/volume Weight/volume % % TYPE I: Grams of solute 100 mL total solution Most common in biology but seldom used in chemistry manuals Technically, the units should be the same in the numerator and denominator 4/28/2020 16
Example 20 g of NaCl in 100 mL of total solution = 20% (w/v) solution. 4/28/2020 17
Example: By Proportions How would you prepare 500 mL of a 5 % (w/v) solution of NaCl? 4/28/2020 18
Answer, By Proportions 5 % = 5 g 100 mL = ? By definition: 5 g 100 mL 500 mL ? = 25 g = amount of solute BTV 500 mL 4/28/2020 19
By Equation How would you prepare 500 mL of a 5 % (w/v) solution of NaCl? 1.Total volume required is 500 mL. 2. 5% = 0.05 3. (0.05) (500 mL) = 25 4. 25 is the amount of solute required in grams. 5. Weigh out 25 g of NaCl. Dissolve it in less than 500 mL of water. 6. In a graduated cylinder or volumetric flask, bring the solution to 500 mL. 4/28/2020 20
4/28/2020 21
Concentration Expressions (Most Common) PARTS (Common in environmental sciences, for example) Amounts of solutes expressed as "parts" a. Parts per Million (ppm) b. Parts per Billion (ppb) c. Might see parts per Thousand (ppt) 4/28/2020 22
Parts Parts may have any units but must be the same for all components of the mixture. 4/28/2020 23
Example: A solution is 3:2:1 ethylene:chloroform:isoamyl alcohol Might combine: 3 liters ethylene 2 liters chloroform 1 liter isoamyl alcohol 4/28/2020 24
Two Other Forms Of % v/v mL solute 100 mL solution w/w g solute 100 g solution 4/28/2020 25
Weight/weight How would you make 500 g of a 5% solution of NaCl by weight (w/w)? 4/28/2020 26
Answer Percent strength is 5% w/w, total weight desired is 500g. 5% = 5g/100g 5g X 500 g = 25 g = NaCl needed 100 g 500 g 25 g = 475 g = amount of solvent needed Dissolve 25 g of NaCl in 475 g of water. 4/28/2020 27
Weight / Volume Means a fraction with: weight of solute in numerator total volume in denominator 4/28/2020 28
Example: 2 mg/mL proteinase K Means 2 mg of proteinase K in each mL of solution. Example: How much proteinase K is required to make 50 mL of solution at a concentration of 2 mg/mL? 4/28/2020 29
Can Solve as A Proportion Problem 2 mg proteinase K = 1 mL solution 50 mL solution X X = 100 mg = amount proteinase K needed. 4/28/2020 30
Volume / Volume Means a fraction with: volume of solute in numerator total volume in denominator Usually the solute here is a liquid as well Remember that volume in the denominator is the total volume of the solution 4/28/2020 31
Example You are to make 50 mL of a 8% v/v solution of diluted dish soap. How many mLs of concentrated dish soap must be added to how many mLs of water? 4/28/2020 32
Weight / Weight Means a fraction with: mass of solute in numerator total mass in denominator Most times the solute here is a solid and sometimes the solution is also a solid Remember that mass in the denominator is the total mass of the solution 4/28/2020 33
Examples You are to prepare 4 kg of specific soil sample which is to be 8% w/w sand and 5% w/w clay in which the remainder is top soil. How many grams of each sand and clay need to be added to the soil to make the solution? 4/28/2020 34
Ppm And Ppb ppm: The number of parts of solute per 1 million parts of total solution. ppb: The number of parts of solute per billion parts of solution. 4/28/2020 35
Ppm Example: 5 ppm chlorine = 5 g of chlorine in 1 million g of solution, or 5 mg chlorine in 1 million mg of solution, or 5 pounds of chlorine in 1 million pounds of solution 4/28/2020 36
Conversions To convert ppm or ppb to simple weight per volume expressions: 5 ppm chlorine 4/28/2020 37
Conversions To convert ppm or ppb to simple weight per volume expressions: 5 ppm chlorine = 5 g chlorine = 5 g chlorine 106 g water 106 mL water = 5 mg/1 L water = 5 X 10-6 g chlorine/ 1 mL water = 5 micrograms/mL 4/28/2020 38
PPM To Micrograms/ml For any solute: 1 ppm in water = 1 microgram mL 4/28/2020 39
Each star represents 1 mg of dioxin. What is the concentration of dioxin in the beaker expressed as ppm (parts per million)? ____________ What is the total amount of dioxin in beaker? ___________ 4/28/2020 40
Each star represents 1 mg of dioxin. What is the total amount of dioxin in tube? 25 mg What is the concentration of dioxin in tube expressed as ppm? ____________ 1 ppm in water = 1 g mL 25 mg/500 mL = 0.05 mg/mL= 50 g/mL so the concentration is 50 ppm 4/28/2020 41
Still More Concentration Expressions TYPES NOT COMMON IN BIOLOGY MANUALS: MOLALITY NORMALITY 1.We remember that for NaOH and HCl, molarity = normality, however, this is not true for all solutes 4/28/2020 42
More with Molarity Molarity is: number of moles of a solute that are dissolved per liter of total solution. By definition: A 1 M solution contains 1 mole of solute per liter total volume. 4/28/2020 43
Mole Mole How much is a mole? 4/28/2020 44
Examples: Water, Sulfuric Acid and Glucose For a particular compound, add the atomic weights of the atoms that compose the compound. What is the formula weight for water H2O? What is the formula weight for sulfuric acid H2SO4? What is the formula weight for glucose C6H12O6? 4/28/2020 45
Example: Sulfuric Acid For a particular compound, add the atomic weights of the atoms that compose the compound. H2SO4: 2 hydrogen atoms 2 X 1.00 g = 2.00 g 1 sulfur atom 1 X 32.06 g = 32.06 g 4 oxygen atoms 4 X 16.00 g = 64.00 g 98.06 g/mole Glucose = 180 g/mole 4/28/2020 46
Example Continued A 1M solution of sulfuric acid contains 98.06 g of sulfuric acid in 1 liter of total solution. Observe that "mole" is an expression of amount Molarity" is an expression of concentration. 4/28/2020 47
Definitions "Millimolar", mM, millimole/L. A millimole is 1/1000 of a mole. "Micromolar", M, mole/L. A mole is 1/1,000,000 of a mole. 4/28/2020 48
Formula HOW MUCH SOLUTE IS NEEDED FOR A SOLUTION OF A PARTICULAR MOLARITY AND VOLUME? FW X molarity x volume = g solute needed 4/28/2020 49
Example How much solute is required to make 300 mL of 0.8 M CaCl2? 4/28/2020 50
