Question

. Given 100mg/L benzoic acid and 200 mg/L caffeine stock solutions, explain how you will make 2, 4, 6, 8, and 10mg/L benzoic acid solutions and 4, 8, 12, 16, and 20 mg/L caffeine solutions. Assume that you will have 50 and 100 mL volumetric flasks and your usual variety of pipet sizes and list the exact volume glassware you would use for each of these dilutions. Be sure to finish this problem and list exact glassware, the answer here is what you will actually be doing in lab!

Answer 1

For

2,4,6,8,10 mg/L stocks:

Apply dilutoin law

C1*V1 = C2*V2

Assume Volume of stock --> 50 mL each

then V2 = 50 mL always

V1 = C2/C1*V2

C1 = always 100 mg/L for benzoic acid, 200 mg/L for caffeine

a)

V1 = C2/C1*V2

V1 = (2/100)*50 = 1 mL

add 1 mL of 100 mg/L solution to the 50 mL beaker, then add remaining water up to V = 50 mL, this will be 2 mg/L in sotck solution

V1 = C2/C1*V2

V1 = (2/100)*50 = 1 mL

add 1 mL of 100 mg/L solution to the 50 mL beaker, then add remaining water up to V = 50 mL, this will be 2 mg/L in sotck solution

b)

V1 = C2/C1*V2

V1 = (4/100)*50 = 2 mL

add 2 mL of 100 mg/L solution to the 50 mL beaker, then add remaining water up to V = 50 mL, this will be 4 mg/L in sotck solution

c)

V1 = C2/C1*V2

V1 = (6/100)*50 = 3 mL

add 3 mL of 100 mg/L solution to the 50 mL beaker, then add remaining water up to V = 50 mL, this will be 6 mg/L in sotck solution

d)

V1 = C2/C1*V2

V1 = (8/100)*50 = 4 mL

add 4 mL of 100 mg/L solution to the 50 mL beaker, then add remaining water up to V = 50 mL, this will be 8 mg/L in sotck solution

e)

V1 = C2/C1*V2

V1 = (10/100)*50 = 5 mL

add 5 mL of 100 mg/L solution to the 50 mL beaker, then add remaining water up to V = 50 mL, this will be 10 mg/L in sotck solution

The same volumes apply for caffeine

since they hare doulbe in concentrations, ans stocks are doulbe

4,8,12,16,20 ( 2x of 2,4,8,10).