Question

make 500mL of 20% methanol (solvent A) per volume with ultra purified water this one is 100mL of methanol and 400mL of purified water

make 100mL 125mg/L caffeine in solvent A 125mg/L * 0.1L =12.5mg = 0.0125mg of caffeine needed

prepare dilution sof caffeine at 100,75,50,25mg/L in 25mL flask with solvent A

to dilute this use how much caffeine solution should I add in volumetric flask and am I right about the sample calculation

Answer 1

Well done! You are absolutely correct about the sample calculation, except for a minor mistake, i.e. 0.0125mg of caffeine needed, it should be 0.0125 g.

(a) M1V1 = M2V2

i.e. 125 mg/L * V1 = 100 mg/L * 25 mL

i.e. V1 = 20 mL

Solution: 20 mL of caffeine solutin and 5 mL of solvent A.

(b) 125 mg/L * V1 = 75 mg/L * 25 mL

i.e. V1 = 15 mL

Solution: 15 mL of caffeine solutin and 10 mL of solvent A.

(c) 125 mg/L * V1 = 50 mg/L * 25 mL

i.e. V1 = 10 mL

Solution: 10 mL of caffeine solutin and 15 mL of solvent A.

(d) 125 mg/L * V1 = 25 mg/L * 25

i.e. V1 = 5 mL

Solution: 5 mL of caffeine solutin and 20 mL of solvent A.