Question

The method of standard additions was used to determine nitrite in a soil sample. A 1.00-mL portion of the sample was mixed with 24.00 mL of a colorimetric reagent, and the nitrite was converted to a colored product that produced a blank-corrected absorbance of 0.250. To 49.00 mL of the original sample, 1.00 mL of a standard solution of 1.00×10-3 M nitrite was added. The same color-forming procedure was followed, and the new absorbance was 0.590. What was the concentration of nitrite in the original undiluted sample?

Concentration = M

Answer 1

To find the concentration of nitrite in the original undiluted sample, use the method of standard additions. By comparing the absorbances, we can determine the concentration of nitrite in the original sample. The concentration is found to be 2.00×10-3 M.

Step-by-step explanation:

To find the concentration of nitrite in the original undiluted sample, we can use the method of standard additions. First, we take a 1.00 mL portion of the sample and mix it with 24.00 mL of a colorimetric reagent to convert nitrite to a colored product. The blank-corrected absorbance of this mixture is 0.250.

Then, we take a 49.00 mL portion of the original sample and add 1.00 mL of a standard solution of 1.00×10-3 M nitrite. The color-forming procedure is followed and the absorbance is measured to be 0.590.

We can use the absorbance values and the known concentration of the standard solution to find the concentration of nitrite in the original undiluted sample. By comparing the absorbances, we find that the increase in absorbance is due to the addition of nitrite from the standard solution. Using the formula:

C2 = C1 × ((A2 - A0) / (A1 - A0))

where C1 is the concentration of the standard solution, C2 is the concentration of the original sample, A1 is the absorbance of the original sample, A2 is the absorbance of the sample with the standard added, and A0 is the blank-corrected absorbance:

C2 = (1.00×10-3 M) × ((0.590 - 0.250) / (0.590 - 0.250)) = 2.00×10-3 M

Therefore, the concentration of nitrite in the original undiluted sample is 2.00×10-3 M.