Question

What is the concentration of the Vitamin C standard solution that you are making?

Using the analytical balance in the instrument room, carefully weigh out about 125 mg of Vitamin C and place it in a 100-mL beaker in approximately 50 mL of water. It is not necessary for you to have exactly 125 mg, but it is important for you to know exactly how many mg you do have, and to make sure none of it is lost in the next steps. After the powder has dissolved, pour the solution into a 100-mL volumetric flask. Rinse the beaker into the flask two times, using about 10 mL of water each time and then fill the flask exactly to the mark (meniscus / mark that shows where exactly 100.00 mL would be) with water. Mix the solution thoroughly by stoppering the flask and shaking and / inverting the flask. What is this initial concentration of Vitamin C? Use a clean 5-mL auto-pipet (ask your instructor for a demonstration of pipetting with the manual pipets) to transfer exactly 5.0 mL of this solution into a clean 100-mL volumetric flask and fill to the mark again with deionized water. Once again, mix the solution thoroughly. Protect the solution from the air. What is this diluted concentration (THIS IS THE ACTUAL STANDARD SOLUTION YOU WILL BE USING)?

Answer 1

Number of moles of Vitamin C = amount in g / molar mass

= 0.125 g / 176.12 g·mol⁻¹

= 7.08*10^-4 moles Vitamin C

Here volume = 100 ml =0.100 L

Molarity = number of moles / volume in L

= 7.08*10^-4 moles Vitamin C / 0.100 L

= 7.08*10^-3 M

This is the initial concentration of Vitamin C

M1V1 = M2V2

Here = M1 = 7.08*10^-3M

V1= 5.0 ML

V2 =100 ml

M2 = ?

M1V1 = M2V2

7.08*10^-3M * 5.0 ml = M2*100 ml

M2 = 7.08*10^-3M * 5.0 ml /100 ml

M2= 3.54*10^-4 M

3.54*10^-4 M is this diluted concentration