Question

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

Answer 1

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

Answer 2

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.

Answer 3

Use that to determine the concentration which would be solving for x.

Answer 4

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.

Answer 5

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.

Answer 6

Sorry it's quite confusing. Is your explanation similar to this video? around 8:37 minutes youtu(dot)be/rllHziqWlgU