The method of standard additions was used to determine nitrite in a soil sample. A 1.00-mL portions of the soil extract sample was transferred to four 25-mL volumetric flasks. To each flask, increment volumes of a 1.00 x10-3M nitrite wasadded according to the table below. A colorimetric reagent was added to each flask to convert the nitrite into a colored product, and finally diluted to volume. What is the concentration of the nitrite in the soil extract based on the absorbance data below (with blank correction included)?
vol. of standard nitrite added, mL Absorbance
5.00 0.079
10.00 0.161
15.00 0.236
20.00 0.318
25.00 0.403
vol. of standard nitrite added, mL
5.00
10.00
15.00
20.00
25.00
Absorbance
0.079
0.161
0.236
0.318
0.403
Plot the data Absorbance on y axis and concentration on the x axis.
Plot the data and determine the slope of the line.
The slope of the line will be the molar absorbtivity or molars extinction coefficient.
Use that to determine the of which would be solving for x.
Use that to determine the concentration which would be solving for x.
Sorry, step 3 and 4 are incorrect.
After solving for the equation of the line use the equation of the line to determine the x intercept.
The absolute value of the X intercept*concentration of the standard should give you the concentration of your sample.
Instead of doing all of this mathematically you can plot the data as Anonymous has suggested, then extrapolate the line at the lower end until it crosses the x axis ON THE LEFT OF THE ORIGIN. That will give you the concentration of nitrite in the original sample. This forum does not allow us to plot the data for you.
Sorry it's quite confusing. Is your explanation similar to this video? around 8:37 minutes youtu(dot)be/rllHziqWlgU
To determine the concentration of nitrite in the soil extract using the method of standard additions, you need to follow these steps:
1. Start by preparing a series of solutions with known concentrations of nitrite. In this case, the known concentration is 1.00 x 10^-3 M.
2. Transfer 1.00 mL of the soil extract sample into each of the four 25 mL volumetric flasks.
3. Add different volumes of the 1.00 x 10^-3 M nitrite standard solution to each flask. The volumes added are given in the table you provided.
4. Next, add a colorimetric reagent to each flask. This reagent converts the nitrite into a colored product. The specific reagent used should be specified in the experimental procedure.
5. Dilute each flask to the volumetric mark with a suitable solvent or buffer solution. This step ensures that the solutions have a consistent total volume.
6. Measure the absorbance of each solution using a spectrophotometer or a colorimeter. The wavelengths used for measurement should also be specified in the experimental procedure.
7. Subtract the absorbance of the blank solution (no nitrite added) from each of the measured absorbance values. This blank correction accounts for any contributions from other sources of absorption in the solution.
8. Plot a graph of the corrected absorbance values against the volume of nitrite added (mL).
9. Draw a best-fit line through the points on the graph. This line will represent the relationship between the concentration of nitrite and the absorbance.
10. Determine the concentration of nitrite in the soil extract by reading the corresponding absorbance value on the best-fit line. The concentration can be obtained by converting the absorbance back to the molar scale using the Beer-Lambert Law.
Please note that without the data for the blank solution (no nitrite added), it is not possible to calculate the concentration of nitrite in the soil extract based on the absorbance data alone.