PREPARING LABORATORY SOLUTIONS AND REAGENTS II: Chapter 22

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PREPARING LABORATORY SOLUTIONS AND REAGENTS II
Chapter 22
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SOLUTIONS WITH MORE THAN ONE SOLUTE

• RECIPE I
• Na2HPO4 6 g
• KH2PO4 3 g
• 0.4 glycerol 10 mL
• Dissolve in water.
• Bring to a volume of 1 liter.
• Recipe lists amounts of solutes.

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• RECIPE II
• 1 M MgCl2
• 0.1 M Tris
• Gives the final concentration of each solute.
• You must calculate the amount of each to use.

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A RECIPE WITH MULTIPLE SOLUTES, SM BUFFER

• SM BUFFER
• 0.1 M NaCl
• 1 mM MgSO4
• 0.2 M Tris, pH 7.5
• 0.01 gelatin

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STRATEGY 1

• PREPARING SM BUFFER WITHOUT STOCK
  SOLUTIONS, OVERVIEW
• Prepare a solution of 0.2 M Tris, pH 7.5.
• Calculate grams of each of the other solutes
  required.
• Weigh out solutes and dissolve directly in Tris
  buffer.

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STRATEGY 1

• 1. Decide how much buffer to make, for example,
  1 liter.
• 2. 1 liter of 0.2 M Tris requires 24.2 g of
  Tris base. (MW 121.1 g/mole.)
• 3. Dissolve Tris in about 700 mL of water and
  bring pH to 7.5.
• Do not bring Tris to volume.

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• 4. 1 liter of 0.1 M NaCl requires 5.84 g of
  NaCl. Add this to Tris buffer.
• 5. 1 liter of 1 mM MgSO4 requires 1/1000 of its
  MW.
• MgSO4 comes in more than one hydrated form
  read container to determine MW.
• Weigh out correct amount.
• Add it to Tris buffer.

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• 6. 0.01 gelatin is 0.1 g in 1 L. Weigh out
  and add to Tris buffer.
• 7. Stir to dissolve.
• 8. BTV 1 L
• 9. Record pH.

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STRATEGY 2

• PREPARING SM BUFFER WITH STOCK SOLUTIONS
• In overview
• Four solutes are each prepared separately as
  concentrated stock solutions.

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• When the four stocks are combined, they dilute
  one another to the proper final concentrations

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STEPS ARE

• 1. Prepare a stock solution of Tris buffer at
  pH 7.5.
• a. No set rule as to what should be
  concentration of stock.
• b. To make 1 L of 1 M stock, dissolve 121.1 g of
  Tris base in about 900 mL of water.
• c. Bring pH to 7.5.
• d. BTV 1L.

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• 2. Prepare a stock solution of magnesium sulfate,
  for example, 1 M.
• To make 100 mL, dissolve 0.1 MW of MgSO4 in
  water, bring to a volume of 100 mL.

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• Prepare a stock solution of NaCl, for example,1
  M.
• To make 100 mL of stock, dissolve 5.84 grams in
  water and BTV 100 mL.

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• Prepare a stock solution of gelatin, for example,
  1.
• Dissolve 1 g in a final volume of 100 mL of
  water.

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• 5. To make the final solution, combine the right
  amounts of each stock.
• Since this is a situation where stocks are
  diluted, use the C1V1 C2V2 equation
• Four times, once for each solute.

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• For example, to calculate how much Tris stock is
  required
• C1 V1 C2 V2
• (1 M) (?) (0.2 M) (1000 mL)
• ? 200 mL

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SUMMARY

• To make 1000 mL of SM buffer, combine
• 200 mL Tris stock
• 1 mL MgSO4 stock
• 100 mL NaCl stock
• 10 mL Gelatin stock
• 7. BTV 1L record pH.

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WHICH STRATEGY?

• Both strategy 1 and 2 are correct.
• Generally efficient to make stock solutions of
  frequently used solutes because weighing out
  chemicals is time-consuming.