“Making solutions with multiple components” Part I: Making solutions from pure reagents

Here is a simple solution containing multiple components: CG 50 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.. CaCl 2 FW = mM = M 1 L(0.050 moles)(111 g) = 5.55 g 1 L 1 mole 5.55 g CaCl 2 Glycerol comes as 100% 1 L = 1000 mL C 1 V 1 = C 2 V 2 (100%) V 1 = (15%)(1000 mL) V 1 = 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 and 150 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.. CaCl 2 FW = mM = M 1 L(0.050 moles)(111 g) = 5.55 g 1 L 1 mole 5.55 g CaCl 2 1 L 50 mM CaCl 2 Step 1: Make 50 mM CaCl 2

Water Glycerol Continue.. Glycerol comes as 100% 1 L = 1000 mL C 1 V 1 = C 2 V 2 (100%) V 1 = (15%)(1000 mL) V 1 = 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 CaCl 2 2 L ?? mM CaCl 2 ?? % glycerol Because.. Don’t do this….

Because… 15% glycerol 50 mM CaCl 2 2 L 25 mM CaCl % glycerol What is the final concentration of CaCl 2 ? C 1 V 1 = C 2 V 2 (50 mM)(1 L)= (C 2 )(2 L) C 2 = 25 mM What is the final concentration of glycerol? C 1 V 1 = C 2 V 2 (15%)(1 L)= (C 2 )(2 L) C 2 = 7.5 % But… I wanted 50 mM CaCl 2, 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….