Laboratory Solutions
In the laboratory, we will be using different concentration of
chemical solutions. Each protocol will require different
solutions in varying concentrations.
Revised 9/06/2006
Concentration
• The amount of a particular
substance in a stated volume (or
sometimes mass) of a solution or
mixture.
• Ratio where the numerator is the
amount of the material of interest
and the denominator is the volume
or mass of the entire mixture.
Concentrations
•weight per volume
•Percents
•Molarity
Weight per Volume
Weight per Volume
• The simplest way to represent
concentration of a solution is as the
mass in grams per unit of volume.
Weight = mass of solute
volume volume of solution
2g NaCl
1L
• Means that 2 g of NaCl is dissolved
in enough liquid so that the total
volume is 1L.
Solute
• The substance
that is being
dissolved
• NaCl
Solvent
• The liquid in
which the solute
is dissolved.
• Water
Amount vs. Concentration
• Amount is how much
substance is present.
• Concentration is ratio with a
numerator (amount) and a
denominator (usually volume)
Proportions
1mg = 10mg
10 mL 100mL
Example 1: How could you make
300 mL of a solution that has a
concentration of 10g of NaCl in 100
mL total solution?
10 g =
?
100 mL
300 mL
300 mL x 10 g = ?
100 mL
.
30 g = ?
Question
1. Your mother gives you 250mg of
acetaminophen and a cup
containing 500ml of water. What
is the concentration of the
solution if you dissolve the
Tylenol in the water?
Question
2. If a solution requires a concentration
of 3g of NaCl in 250 mL total
volume, how much NaCl is required
to make 100mL?
Question
3. How many milligrams of NaCl are
present in 50 mL of a solution
that has a concentration of
2mg/mL NaCl?
Question
4. If the concentration of MgSO4 in a
solution is 25 g/L, how much
magnesium sulfate is present in
100mL of this solution?
Question
5. If a solution requires .005 g of Tris
base per Liter, how much Tris Base
is required to make 10-3 Liters of
this solution?
Percentage
Concentrations
Percentage Concentrations
When concentration is expressed in
terms of percent, the numerator
is the amount of solute and the
denominator is 100 units of total
solution.
• weight/volume percent
• volume percent
• weight percent
Weight/Volume Percent
A weight per volume percent
concentration is the weight of the
solute in grams per 100 mL of solution.
It can be abbreviated as w/v.
Weight/Volume % = grams of solute x 100
volume of solution
Example 2
A student adds 20.0 grams of NaCl to
volumetric flask and fills it to the 100mL
mark. What is the weight per volume (w/v)
percent concentration of the solution?
Weight % =
Weight % =
Weight % =
grams of solute x 100
volume of solution
20.0 grams x 100
100mL of solution
20% NaCl solution
6. A student adds 13.5 grams of KCl to
volumetric flask and fills it to the
1000mL mark. What is the weight
per volume percent of the solution?
7. A student adds 45.6 grams of MgCl2
to volumetric flask and fills it to the
1000mL mark. What is the weight
per volume percent of the solution?
By rearranging the equation we can
determine how much chemical we
needed to add to the desired volume to
prepare a solution of the correct
concentration.
Grams of solute = Volume of solution x W/V %
Example 3
How many grams of NaCl would be needed to
prepare 500 ml of a 5% solution of NaCl?
Grams of solute
= Volume of solution x Weight %
Grams of solute = 500mL x 5%
Grams of solute = 500mL x 5g/100mL
Grams of solute = 25 g of NaCl
8. How many grams of NaCl would be
needed to prepare 250 ml of a 5%
solution of NaCl?
9. How many grams of Glucose would be
needed to prepare 200 ml of a 2%
solution of glucose?
10. How many grams of EDTA would be
needed to prepare 475 ml of a 15%
solution of EDTA?
11. How many grams of Pb(NO3)2 would be
needed to prepare 500 ml of a 5%
solution of Pb(NO3)2?
Volume/Volume Percent
In a percent by volume expression, both
the amount of solute and the total solution
are expressed in volume units. It can be
abbreviated as v/v.
volume % = volume of solute x 100
volume of solution
Volume % = mL of solute x 100
100 mL of solution
Example 4
A student adds 20.0 ml of ethanol to volumetric
flask and fills it to the 1L mark. What is the
percent volume (v/v) concentration of the
solution?
Volume % =
Volume % =
Volume % =
volume of solute x 100
volume of solution
20.0 mL of solute x 100
1000mL of solution
2%
12. A student adds 10.0 ml of ethanol to
100mL volumetric flask and fills it to
the mark. What is the percent volume
(v/v) concentration of the solution?
13. A student adds 3.5 ml of isopropanol to
50mL volumetric flask and fills it to the
mark. What is the percent volume (v/v)
concentration of the solution?
14. A student adds 1.5 ml of methanol to
100mL volumetric flask and fills it to
the mark. What is the percent per
volume (v/v) concentration of the
solution?
By rearranging the equation we can determine
the volume the chemical solution we needed to
add to the desired volume to have a solution of
the correct concentration.
Volume of solute = Volume of solution x Volume %
Example 5
How many milliliters of ethanol would you
need to make 10.0 mL of a 10% by volume
solution of ethanol in water?
volume of solute = Volume of solution x Volume /volume %
volume of solute = 10.0 ml x 10%
volume of solute = 1.0 ml ethanol
15. How many milliliters of ethanol would you
need to make 20.0 mL of a 10% by
volume solution of ethanol in water?
volume of solute = Volume of solution x Volume /volume %
16. How many milliliters of isopropyl alcohol
would you need to make 100 mL of a
75% by volume solution of isopropyl
alcohol in water?
volume of solute = Volume of solution x Volume /volume %
17. How many milliliters of methanol would
you need to make 1L of a 90% by
volume solution of methanol in water?
volume of solute = Volume of solution x Volume /volume %
18. How many milliliters of bleach would you
need to make 1L of a 20% by volume
solution of bleach water?
volume of solute = Volume of solution x Volume /volume %
19. How many milliliters of SDS solution
would you need to make 1L of a .1 %
by volume solution of SDS buffer?
volume of solute = Volume of solution x Volume /volume %
Weight Percent
In a Weight (mass) Percent the
numerator is the mass of solute and the
denominator is mass of total solution.
Weight % =
weight of solute
weight of solution x 100
Example 6: What is the weight percent
of glucose in a solution made by
dissolving 4.6 g of glucose in 145.2 g of
water?
Determine total weight of solution:
4.6 g glucose
+ 145.2 g water
149.8 g solution
Calculate Weight % glucose =
4.6 g glucose x 100 = 3.1% glucose
149.8 g solution
20. What is the weight percent of sucrose in a
solution made by dissolving 29.89 g of
sucrose in 1000 g of water?
21. What is the weight percent of NaCl in a
solution made by dissolving 123.5 g of
NaCl in 898 g of water?
By rearranging the equation we can
determine the mass of the chemical
we needed to make the solution of
the correct concentration.
Grams of solute = Gram of solution x Weight/Weight %
Example 7: How much NaCl would you need to
prepare 400 g of a 2.50% solution of sodium
chloride?
Grams of solute = Gram of solution x Weight/Weight %
Grams of solute = 400 g x 2.50 %
Grams of solute = 10.0 g salt
22. How much KCl would you need to prepare
300g of a 25% solution of KCl?
Grams of solute = Gram of solution x Weight/Weight %
23. How much AgNO3 would you need to
prepare 150 g of a 3.0% solution of Ag
NO3?
Grams of solute = Gram of solution x Weight/Weight %
24. How much resin would you need to
prepare 200 g of a 75% solution of resin
in acetone?
Grams of solute = Gram of solution x Weight/Weight %
Homework Problems
1. A chemist adds 78.5 grams of
MgCl2 to volumetric flask and fills it
to the 1L line. What is the weigh per
volume percent of the solution?
Weight % =
Weight % =
grams of solute x 100
volume of solution
78.5 g x 100
1000mL of solution
2. How many grams of NaCl
would be needed to prepare 600
ml of a 34% solution?
Grams of solute = Volume of solution x W/V %
3. How many grams of KCl
would be needed to prepare
.4 L of a 25% solution?
4. How many grams would be
needed to prepare an 11%
solution of sucrose in 350 ml?
5. Find amount of milligrams
present in: 75 mL CaCO3
solution with a
concentration of 3 mg/ml.
6. A student adds 20 ml of methanol
to 400ml flask and fills it to the
mark. What is the percent per
volume (v/v) concentration of the
solution?
7. 37ml of a substance is put
into a 500 ml flask filling it.
What is the v/v concentration
of the solution?
8. 50 ml of a substance is added into
a 1.25 L flask, filling it. What is the
percent volume concentration of the
solution?
9. How many milliliters of
ethanol would you need to
make 100 mL of a 23% by
volume solution?
10. What is the weight percent
of NaCl in a solution made by
dissolving 480 g of NaCl in
1000 g of water?
Weight % =
weight of solute
weight of solution x 100
11. How much MgCO3 would
you need to make 120g of an
8.5% solution of MgCO3?
12. What is the weight percent
of sucrose in a solution
made by dissolving 50 g
in 350 g of water?
Weight % =
weight of solute
weight of solution x 100