Laboratory Solutions

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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
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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.

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Concentrations

• weight per volume
• Percents
• Molarity

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Weight per Volume
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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 

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• 2g NaCl
• 1L
• Means that 2 g of NaCl is dissolved in enough
  liquid so that the total volume is 1L.

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Solute

• The substance that is being dissolved
• NaCl

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Solvent

• The liquid in which the solute is dissolved.
• Water

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Amount vs. Concentration

• Amount is how much substance is present.
• Concentration is ratio with a numerator (amount)
  and a denominator (usually volume)

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Proportions

• 1mg 10mg
• 10 mL 100mL

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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 ?

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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?

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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?

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Question

• 3. How many milligrams of NaCl are present in 50
  mL of a solution that has a concentration of
  2mg/mL NaCl?

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Question

1. If the concentration of MgSO4 in a solution is 25
   g/L, how much magnesium sulfate is present in
   100mL of this solution?

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Question

1. 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?

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Percentage Concentrations
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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

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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

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Example 2A 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 grams of solute x 100
  volume of solution
• Weight 20.0 grams x 100 100mL
  of solution
• Weight 20 NaCl solution

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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?
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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?
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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

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Example 3How 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

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8. How many grams of NaCl would be needed to
prepare 250 ml of a 5 solution of NaCl?
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9. How many grams of Glucose would be needed to
prepare 200 ml of a 2 solution of glucose?
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10. How many grams of EDTA would be needed to
prepare 475 ml of a 15 solution of EDTA?
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11. How many grams of Pb(NO3)2 would be needed to
prepare 500 ml of a 5 solution of Pb(NO3)2?
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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

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Example 4A 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 of solute x 100
• volume of solution
• Volume 20.0 mL of solute x 100
• 1000mL of solution
• Volume 2

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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?
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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?
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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?
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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

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Example 5How 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

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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
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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
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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
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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
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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
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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

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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

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20. What is the weight percent of sucrose in a
solution made by dissolving 29.89 g of sucrose in
1000 g of water?
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21. What is the weight percent of NaCl in a
solution made by dissolving 123.5 g of NaCl in
898 g of water?
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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

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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

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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

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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

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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

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Homework Problems
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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 grams of solute x 100
  volume of solution
• Weight 78.5 g x 100 1000mL of
  solution

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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

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3. How many grams of KCl would be needed to
prepare .4 L of a 25 solution?
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4. How many grams would be needed to prepare an
11 solution of sucrose in 350 ml?
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5. Find amount of milligrams present in 75 mL
CaCO3 solution with a concentration of 3 mg/ml.
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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?
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7. 37ml of a substance is put into a 500 ml flask
filling it. What is the v/v concentration of the
solution?
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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?
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9. How many milliliters of ethanol would you need
to make 100 mL of a 23 by volume solution?
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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

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11. How much MgCO3 would you need to make 120g
of an 8.5 solution of MgCO3?
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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