Question

[Caluculating concentrations of solutions]
I have to make a calibration curve between absorbance and concentraions. However, I don' know exactly how to calculate my serially dilluted concentrations.

1. There's crystal violet of 2ml and that was 0.0001M and I soaked it with 48ml of methanol.
and I prepared 4 flasks.
2.I took 16 ml of cv from #1 and soaked with methanol until total volume be 50mL(So methanol's volume was 34mL).
3. and I consequently soaked 12mL of cv with 38mL of metahnol, 8mL of cv with 42mL of methanol lastly 4mL of cv with 46mL of metahnol.

I finished all my experiments but it is vague how to correctly calculate my concentrations. Please let me know with your explanation. Thanks in advance!

Answer 1

1. Total volume of the solution = ( 2 + 48 ) mL = 50 mL

Concentration of CV in the solution = initial concentration * initial volume / Final volume = 0.0001 M * 2 ml/ 50 ml = 0.000004 M

2. 16 mL of the 0.000004 M of CV solution is dilute to a final volume of 50 mL.

Concentration of CV in the new solution = initial concentration * initial volume / Final volume = 0.000004 M * 16 mL/ 50 mL = 0.00000128 M

3. Part 1: 12 mL of 0.00000128 M of CV solution is added to 38 mL of methanol. Final volume of the resulting solution is ( 12 + 38) ml = 50 ml.

Concentration of CV in the reulting solution = initial concentration * initial volume / Final volume

= 0.00000128 M * 12 mL/ 50 mL = 3.072 * 10^-7 M

Part 2: 8 mL of 0.00000128 M of CV solution is added to 42 mL of methanol. Final volume of the resulting solution is ( 8 + 42) ml = 50 ml.

Concentration of CV in the reulting solution = initial concentration * initial volume / Final volume

= 0.00000128 M * 8 mL/ 50 mL = 2.048 * 10^-7 M

Part 3: 4 mL of 0.00000128 M of CV solution is added to 46 mL of methanol. Final volume of the resulting solution is ( 4 + 46) ml = 50 ml.

Concentration of CV in the reulting solution = initial concentration * initial volume / Final volume

= 0.00000128 M * 4 mL/ 50 mL = 1.024 * 10^-7 M