Serial Dilutions
You transfer 1 mL of bacterial culture into 9 mL of sterile PBS. What is the dilution factor?
1:10 or 10^-1
Which growth phase is characterized by bacteria rapidly dividing?
Log/Exponential phase
What equation is commonly used to calculate solution dilutions?
C1V1 = C2V2
How many moles are present in 5 L of a 1M solution?
Hint: M (mole/L)
5 moles
What is a stock solution?
A concentrated solution that is diluted to make working solutions
You perform two consecutive 1:10 dilutions. What is the final dilution?
Hint: Think about the 8-well strip dilution activity
1:100 or 10^-2
A bacterial culture doubles every 30 minutes. How many generations occur in 2 hours?
4 generations
20 mL
How many grams of NaCl are needed to make 500 mL of a 0.5 M NaCl solution?
NaCl MW = 58.44 g/mol
14.61 g
You have a 10x stock solution. What does 10x mean?
The stock is 10 times the concentration of a 1x working solution
You have a 1:100 dilution and transfer 10uL into 90uL of sterile PBS. What is your new dilution?
1:1000 or 10^-3
A culture starts with 1,000 cells and doubles every 20 minutes. How many cells will there be after 1 hour?
8,000 cells
You have a 20% stock solution. You need 75 mL of a 3% solution. How much stock and diluent do you need?
11.25 mL stock + 63.75 mL diluent
A solution contains 3 moles of solute in 2 L of solution. What is its molarity?
1.5M
You need 100 mL of a 1x solution from a 10x stock. How much diluent and 10x stock are needed?
Hint: 1:10 dilution
10 mL stock + 90 mL diluent
You serially dilute a pure saliva sample and obtain the given bacterial counts. What is the CFU/mL of the undiluted sample?
10-5 | 1247
10-6 | 219
10-7 | 18
2.19E8 CFU/mL
If a culture has 14 cells at t=0 and 112 cells at t=6 hrs, what is its generation time?
2 hours
Your lab instructor asks you to prepare 50 mL of a 3% agarose gel. How many grams of agarose do you need?
Hint: 3g/100mL agarose
0.025 mol
You need 500 mL of a 1x solution from a 20x stock. How much stock and diluent are needed?
25 mL stock + 475 mL diluent
You serially dilute a pure saliva sample and obtain the given bacterial counts. What is the CFU/mL of the undiluted sample?
10-5 | 258
10-6 | 137
10-7 | 21
8.14x10^7
If a culture’s generation time is 27.2 hours and it starts with 4 cells, how many cells will it have after 54.4 hours?
16
How much water (in mL) is needed to dilute a solution of 194-proof ethanol to make 200 mL of 60% ethanol?
(Hint: Proof = 2 × % alcohol)
76.3
You are preparing a bacterial culture medium that required 0.25 M NaCl. You need 200 mL of medium. NaCl has a MW of 58.44 g/mol. How many grams of NaCl are required?
2.922g
LAB SCENARIO:
You need 60 mL of 0.5% KOH + 3% H2O2 (bleach) for a staining procedure. Your available solutions are 1% KOH and 10% H2O2. How much of each stock solution and water do you need?
Hint: calculate 2 dilutions and determine the final volume
30 mL 1% KOH, 18 mL 10% H2O2, and 12 mL H2O