Department of Chemistry and Geosciences

Honors 1084 Lab Spring 2006

Lab Test 7

Name:_________________________________________________ Section:

Answer the following questions to the best of your ability showing all work necessary to obtain the answer. The answer must be given with the correct units and the correct number of significant figures where applicable. Remember to show all your work necessary to obtain the answer. Simply writing the correct answer without showing any work may not receive full credit.

1. (40 points) A solution is prepared by diluting 7.50 mL of a standard solution of nitrate ion of concentration of 50 mg/L to 50.00 mL. What is the concentration, in mg/L, of the diluted nitrate ion solution?

Using the dilution formula:

2 . (40 points) A student prepared a Beer’s Law plot of absorbance versus concentration from the results obtained in last week’s experiment:

___ The absorbance of the river water sample was measured at 0.612. What is the concentration of NO₃¯ ion in the water sample in units of mg/L?

The slope of the line above is the extinction coefficient. It is equal to 0.0547 1/(mg·L)cm. The concentration of NO₃¯ in a solution with an absorbance of 0.612 is equal to (using Beer’s Law):

3. (20 points) Define oxidation and oxidizing agent:

Oxidation is the loss of electrons.

An oxidizing agent causes another substance to get oxidized.