# PREPARING LABORATORY SOLUTIONS AND REAGENTS II

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PREPARING LABORATORY SOLUTIONS AND REAGENTS II

Solutions With More Than One Solute
RECIPE I Na2HPO g KH2PO g 0.4% glycerol 10 mL Dissolve in water. Bring to a volume of 1 liter. Recipe lists amounts of solutes. This is easy to follow

Solutions With More Than One Solute Cont…
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. This is harder to interpret

A Recipe With Multiple Solutes, SM Buffer
0.1 M NaCl 1 mM MgSO4 0.2 M Tris, pH 7.5 0.01% gelatin This might be whole recipe as given in a manual

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.

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

4. 1 liter of 0. 1 M NaCl requires 5. 84 g of NaCl
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.

0.01% gelatin is 0.1 g in 1 L. Weigh out and add to Tris buffer.
Stir to dissolve BTV 1 L Check and record pH.

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

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

Steps Are: Prepare a stock solution of Tris buffer at pH 7.5.
a. No set rule as to what should be concentration of stock. b. Example: To make 1 L of 1 M stock, dissolve g of Tris base in about 900 mL of water.

c. Bring pH to 7.5. d. BTV 1L. 2. Prepare a stock solution of magnesium sulfate, for example, 1 M. a. To make 100 mL, dissolve 0.1 MW of MgSO4 in water, bring to a volume of 100 mL.

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

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

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

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

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 BTV 1L; check and record pH.

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.