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PREPARING LABORATORY SOLUTIONS AND REAGENTS II: Chapter 22

PREPARING LABORATORY SOLUTIONS AND REAGENTS II: Chapter 22. SOLUTIONS WITH MORE THAN ONE SOLUTE. RECIPE I Na 2 HPO 4 6 g KH 2 PO 4 3 g 0.4% glycerol 10 mL Dissolve in water. Bring to a volume of 1 liter. Recipe lists amounts of solutes. RECIPE II

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PREPARING LABORATORY SOLUTIONS AND REAGENTS II: Chapter 22

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  1. PREPARING LABORATORY SOLUTIONS AND REAGENTS II: Chapter 22

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. STRATEGY 2: PREPARING SM BUFFER WITH STOCK SOLUTIONS • In overview: • Four solutes are each prepared separately as concentrated stock solutions.

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

  11. 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.

  12. 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.

  13. 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.

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

  15. 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.

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

  17. 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.

  18. 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.

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