Lecture 1 Dilutions

Question 1

What are dilutions? Purpose for dilutions?

Answer 1

From a higher concentration to a new, more dilute concentration by adding water or a buffer solution.

Dilutions are used to prepare new working solutions from previously made stock solutions, saving a lot of time.

Dilutions can be used to make standard mixtures to conduct an assay. As well as make serial dilutions to find the right antibody titer (level) or enzyme activity level or to dilute live cells

Question 2

What is the equation for only adding water to dilute a solution? What are the variables?

Answer 2

C x V = A

C - concentration of substance (will change)
V - volume of solution (will change)
A - total amount of substance in the solution (will NOT change)

Question 3

What are the ways of identifying the problem for dilutions?

Answer 3

• Dilute the whole thing to desired final conc.
• Dilute to desired final concentration and volume
• Prepare a dilution from a stock solution

Question 4

What is the dilution equation?

Answer 4

C1 V1 = C2 V2

Question 4

Ex. Dilute 10 mL of 0.125 M NaCl to 0.025 M

Answer 4

V1 = 10 mL = 0.01 L
C1 = 0.125 M
C2 = 0.025 M
V2 = (0.125 M)(0.01 L)/(0.025 M) = 0.05 L = 50 mL

Question 5

Ex. Prepare 500 uL of 3 mg/mL lysozyme where the stock concentration is 25 mg/mL

Answer 5

V2 = 500 uL = 0.5 mL
C2 = 3 mg/mL
C1 = 25 mg/mL
V1 = (3 mg/mL)(0.5 mL)/(25 mg/mL) = 0.06 mL = 60 uL

To make 500 uL, bring 60 uL to final volume of 500 uL by adding H2O

Question 5

Ex. 1% NaCl (w/v)

Answer 5

1 g of NaCl in final volume of 100 mL

Question 6

What are percent (%) solutions?

Answer 6

The amount of a substance (either solid or liquid) is expressed as a percentage of the total solution volume

Ex. 1% solution means that there is 1 g or 1 mL of the substance in 100 mL of 100 g of the final solution/weight

Question 7

Ex. 10 % glycerol (v/v)

Answer 7

10 mL of glycerol in final volume of 100 mL

Question 8

What are the stock solution terms?

Answer 8

Working solution = diluted stock solution
Stock solution = stored concentrate
Dilution factor = ratio of stock concentration to working concentration

Question 9

Ex. Stock concentration = 500 mM
Working concentration = 50 mM
What is the dilution factor?

Answer 9

Dilution factor = 10X

Question 10

Why are stock solutions useful?

Answer 10

• Can be used to prepare different working solutions that share the same components but in different proportions
• Stock solutions are better for making very dilute buffer solutions because it can be pipetted as a small liquid volume more accurately than weighed as an amount of dry chemical
• Stock solutions can be used as a component of a more complex solution