A standard addition method is used to determine the concentration of ethanol in an
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
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
To determine the concentration of ethanol in the unknown sample, we can use the standard addition method. This method involves adding a known amount of standard solution to the unknown sample and measuring the resulting concentration.
In this case, we have six aliquots of the unknown, each with a volume of 10 mL. We also have a standardized ethanol solution with a concentration of 1.57 g/L.
First, we need to measure the volume of the ethanol standard solution added to each of the aliquots. The volumes are given as 5.00 mL, 10.00 mL, 15.00 mL, 20.00 mL, and 25.00 mL.
Next, each of the aliquots is diluted to a total volume of 50.00 mL. This means that the volume of the unknown sample in each aliquot is 10 mL, and the volume of the ethanol standard solution is the volume added from the previous step, plus the remaining volume up to 50 mL.
Now, we need to measure the absorbance spectrum of each of the six solutions. The absorbance spectrum is a measure of how much light is absorbed by the sample at different wavelengths. In this case, we are interested in the ethanol region.
After obtaining the absorbance spectrum, we need to calculate the relative area under the curve for each solution. This can be done by integrating the absorbance values over the range of interest.
Finally, we can use the relative areas and the known concentration of the ethanol standard solution to calculate the concentration of ethanol in the unknown sample. We can use a linear regression analysis to determine the relationship between the relative areas and the ethanol concentrations.
To determine the 95% confidence limits for the answer, we can use statistical analysis. This typically involves calculating the standard deviation of the measurements and using it to calculate the confidence interval. The confidence interval provides a range within which we can be 95% confident that the true concentration of ethanol in the unknown sample lies.