Making Solutions

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PREPARING SOLUTIONS AND REAGENTS
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Chemical Solutions (aqueous water is the
solvent)

• Types of vessels (least to most precise)
• Beaker
• Erlennmeyer flask
• Graduated cylinder
• Volumetric flask

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• DEFINITIONS
• SOLUTES -- substances that are dissolved
• SOLVENTS -- substance in which solutes are
  dissolved (usually water)
• AMOUNT -- how much

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Goals

• Make solutions
• Dilute solutions
• Convert between different concentrations of
  solutions

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Facts of Life

• Mass is measured in Grams, mg, µg
• 1g 1000mg 1,000,000µg
• Volume is measured in liters, mL, µL
• 1L 1000mL 1,000,000 µL
• Density of water is 1 g / mL

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Facts of life (contd)

• Concentration means amount of solute in a volume
  of solution
• Expressed in many ways
• 1. percent
• 2. mg/ mL
• 3. molar
• 4. X solution

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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)?
_____  
5 mg ? 8 mL 1 mL ? 0.63 mg, so the
concentration is 0.63 mg/mL
8 mL
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Percent Solutions

• Per means for every one
• Cent means 100
• Example a 5 sugar solution has
• 5 grams of sugar for 100g of solution, or
• 5g 100 g of water 100 mL, and the
• 100mL solution is mostly water.

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Make 250 mL of a 3 starch solution

• 3 g / 100 g 3 g / 100 mL because density of
  water is 1 g / mL
• Set up a ratio
• 3 g / 100 mL ?g / 250 mL
• Use 7.5 g of starch and bring to a volume of
  (BTV) 250 mL with distilled water

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mg / mL Solutions

• 5 mg/mL has 5 milligrams of solute in 1
  milliliter of solution

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Make a 250 mL of a 3 mg /mL starch solution

• Set up a ratio
• 3 mg / 1 mL ?mg / 250 mL
• Use 750 mg of starch and bring to a volume of
  (BTV) 250 mL with distilled water

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Molar Solutions

• 1 mole is 6.02 x 1023 items
• Molecular weight or Formula weight is really the
  mass of 1 mole of molecules (see periodic table)
• Example 1 mol of sodium chloride (NaCl) has a
  mass of 58.44 g.

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MOLARITY

• Molarity is number of moles of a solute that
  are dissolved per liter of total solution.
• A 1 M solution contains 1 mole of solute per
  liter total volume.

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MOLE

• How much is a mole?

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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

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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.
• "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?
• (g solute ) X (mole) X (L) g solute
  needed
• 1 mole L
• or
• FW X molarity x volume g solute
  needed

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EXAMPLE

• How much solute is required to make 300 mL of 0.8
  M CaCl2?

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ANSWER

• (111.0 g) x (0.8 mole) x (0.3 L) 26.64 g
• mole L

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• Make 250 mL of a 3 molar NaCl solution
• 58.44g x 3 moles x 0.25 L ? g
• 1 mole 1 L
• ? 43.8g of NaCl
• BTV of 250 mL

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X solutions

• X means times
• A 40X buffer solution is 40 times more
  concentrated than the standard working solution
• Stock solutions / concentrates
• How much stock solution you need total volume
  you need divided by the X number

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Diluting Solutions

• Conc 1 x Vol. 1 Conc 2 x Vol 2
• Usually want 1 X solutions

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Example Frozen Orange Juice

• Solution 1 is the frozen concentrate
• Solution 2 is the 1X juice you drink
• How concentrated is it?
• C1 V1 C2 V2
• (? X) (250mL) (1X) (1000 mL)

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Answer Frozen OJ is 4X because ¼ of the final
volume is the concentrated oj
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Example bleach sterilant

• Solution 1 is 100 bleach stock solution
• Solution 2 is 6 bleach what you want
• How do you make 350 mL of 6 bleach?
• C1 V1 C2 V2
• (100) (?) (6) (350 mL)

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Answer You need 21 mL of 100 bleachBTV 350
mL.