Simple and Serial Dilutions

Question 1

when can you use simple dilutions?

Answer 1

• potato osmosis practical
• glucose practical
• beetroot practical

Question 2

how can you dilute solutions?

Answer 2

add distilled water

Question 3

formula to answer simple dilution q?

Answer 3

C1V1 = C2V2

• C1 = conc of stock at start - mol/dm3
• V1 = vol of stock need use - cm3 or ml
• C2 = final conc want make - mol/dm3
• V2 = final vol want make - cm3 or ml

Question 4

make 100ml of 0.5mol/dm3 glucose solution from 1M stock?

Answer 4

• want to find V1
• V2 = 100ml
• C2 = 0.5mol/dm3
• C1 = 1mol/dm3
• V1 = C2V2 / C1
• 100x0.5 / 1

= 50ml

SO 50 MOL OF STOCK AND 50 ML DISTILLED WATER

Question 5

when can you use serial dilutions?

why?

Answer 5

culturing bacteria

• too much to count
• DO 10 FOLD SERIAL DILUTION

Question 6

describe how scientists couls obtain data to produce calibration curve and how they would use the calibration curve to find the concentration of glucose in a sample of blood plasma?

Answer 6

• produce known conc of glucose
• measure absorbance at each conc
• plot graph with conc on x-axis and light absorbance on y-axis

Question 7

a student used a dilution series to investigate the number of cells present in a liquid culture of bacteria.

describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original culture of bacteria?

Answer 7

• put 10 ml of pure culture into 90ml of water
• MIX
• repeat using 9 parts fresh liquid and 1 part of 10^-1 until = 10^-3

Question 8

a student looked at cells in 1 in 10 dilution during his preliminary work.

he decided not to use this dilution to determine the number of cells in the undiluted liquid culture.

suggest an explanation for this?

Answer 8

count unlikely to = accurate because too many cells