A standard addition method is used to determine the concentration of ethanol in an

Question

unknown sample. Six 10 mL aliquots of the unknown are drawn from the processing
vat. An aqueous solution of ethanol is standardized to have 1.57 g/L. This standard is
pipetted to five of the aliquots in the following volumes: 5.00 mL, 10.00 mL, 15.00 mL,
20.00 mL, and 25.00 mL. Each of the six solutions is then diluted to a total volume of
50.00 mL. Three samples are taken from each of these solutions and the absorbance
spectrum in the ethanol region is measured and the relative area under the curve is reported.Determine the concentration of ethanol in this unknown sample and provide the 95%
confidence limits for the answer

Answer 1

Making ethanol concentrations of:

0.40%
0.30%
0.20%
0.10%
0.05%

To make the 0.40% ethanol from stock solution using 100ml volumetric flask:

(xg ethanol)/(100ml) x 100= 0.40%
xg= 0.4g ethanol

Then 0.4g ethanol solution is added to a 100ml volumetric flask with water in it already. After the addition of 0.4g ethanol into the flask whilst weighing it on a balance.

Then I take that 0.40% solution of ethanol and dilute it with
M1V1=M2V2

To get 10ml of 0.30% ethanol solution:
Find out how much of stock is needed to dilute
(0.40%)(V1)=(0.30%)(10ml)
V1= 7.5ml ethanol

add that 7.5ml ethanol into a 10ml volumetric flask and add water to the line to get 0.3% ethanol solution

To get 10ml of 0.20% ethanol solution:
Find out how much of stock is needed to dilute
(0.40%)(V1)=(0.20%)(10ml)
V1=5 ml ethanol

add that 5 ml ethanol into a 10ml volumetric flask and add water to the line to get 0.2% ethanol solution

same process for the below concentrations..just checking my calculations:

0.1% ethanol solution:
(0.40%)(V1)=(0.10%)(10ml)
V1=2.5 ml ethanol

0.05% ethanol solution:
(0.40%)(V1)=(0.05%)(10ml)
V1=1.25 ml ethanol

I'm not sure if I can use percentage for the dilution equation, or if I can even use grams for the creation of the original solution

Thanks very much