“Making solutions with multiple components”

Part I: Making solutions from pure reagents

Here is a simple solution containing multiple components:

CG50 mM calcium chloride

15% glycerol

The most confusing thing about solutions such as these is the way they look on paper!!

This is ONE solution with multiple components…

Making CG: Calcium chloride and glycerol are added to water such that you make one solution with a final concentration of 50 mM calcium chloride and 15% glycerol

Calcium chloride

Water Glycerol Continue..

Done!

CG

50 mM calcium chloride

15% glycerol

Making CG: Calcium chloride and glycerol are added to water such that you make one solution with a final concentration of 50 mM calcium chloride and 15% glycerol

Doing the math…

• Here’s another confusing part…• You do the calculations for solutions

containing multiple components as if you were making several single component solutions…

Let’s do the math…

Calcium chloride

Water Glycerol Continue..

CaCl2 FW = 11150 mM = 0.050 M1 L(0.050 moles)(111 g) = 5.55 g

1 L 1 mole

5.55 g CaCl2

Glycerol comes as 100%1 L = 1000 mLC1V1 = C2V2

(100%) V1 = (15%)(1000 mL)V1 = 150 mL

150 mL

Making CG: Calcium chloride and glycerol are added to water such that you make one solution with a final concentration of 50 mM calcium chloride and 15% glycerol

Let’s make 1 L of CG…

Making CG:To make 1 L of this solution, 5.55 g of calcium chloride and150 mL of 100% glycerol were added to enough water to make 1 L total of solution.

Done!

CG

50 mM calcium chloride

15% glycerol

1 L

A common error to watch for…

• Because the calculations for multiple component solutions are done separately (as if you were making several single component solutions), students sometimes want to just mix single component solutions together…

Don’t do this….

Calcium chloride

Water Continue..

CaCl2 FW = 11150 mM = 0.050 M1 L(0.050 moles)(111 g) = 5.55 g

1 L 1 mole

5.55 g CaCl21 L

50 mM CaCl2

Step 1: Make 50 mM CaCl2

Water Glycerol Continue..

Glycerol comes as 100%1 L = 1000 mLC1V1 = C2V2

(100%) V1 = (15%)(1000 mL)V1 = 150 mL

150 mL

1 L

15% glycerol

Step 2: Make 15% glycerol

Don’t do this….

Step 3:And combine the two…

1 L

15% glycerol

1 L

50 mM CaCl2

2 L?? mM CaCl2

?? % glycerol

Because..

Don’t do this….

Because…

15% glycerol50 mM CaCl2

2 L25 mM CaCl2

7.5 % glycerol

What is the final concentration of CaCl2?C1V1 = C2V2

(50 mM)(1 L)= (C2)(2 L)C2 = 25 mM What is the final concentration of glycerol?C1V1 = C2V2

(15%)(1 L)= (C2)(2 L)C2 = 7.5 %

But… I wanted 50 mM CaCl2, 15% glycerol!! Hmm..If you first make two solutions of the desired concentration, and add them together, you are diluting each!!

Don’t do this….