1. You send a sample of rice to the lab for the determination of the total arsenic content. The analyst dissolves 525 mg of the rice in 5.0 mL of concentrated acid and then dilutes the solution to a final volume of 20.0 mL. When analyzed by ICP-MS, the solution concentration is found to be 20 g L^-1. What is the concentration of arsenic in the rice (in g kg^-1)?

2. The density of a solution, made by dissolving a pure chemical in water, is 1.40 g per mL. What volume would 100 g of the solution occupy? ___________

If 25.0% of the weight of the solution is the solute (the compound dissolved) what is the concentration in g per L? ___________

If the molecular weight of the compound is 168 g mol^-1, what is the concentration of the solution in M? ___________

3. In the food-processing lab you are making white rice by removing the rice bran from brown rice. If the bran contains 768 ppb of arsenic and the brown rice contains 342 ppb, what is the concentration in the white rice if you remove 10.0% of the mass during the milling process? ___________

4. Your drinking water contains 4.0 ppb inorganic arsenic. You drink 1.0 L per day and when cooking rice use 500 mL by a method in which all of the water is absorbed. If you eat 50 g of rice containing 150 ppb of inorganic arsenic three-times per week and you weigh 70 kg, what is your dose (in g per kg of body weight per day)? ___________

5. The Hach chemical company makes a test kit based on the Gutzeit-Marsh reaction. I am trying to adapt this for the determination of inorganic arsenic in rice, and have modified the test so it has a detection limit of 2 ppb for inorganic arsenic in a 100-mL sample of drinking water. Undergraduate researchers in my group have shown that all the inorganic arsenic in 10 g of rice can be extracted into 100 mL of dilute acid. What is the lowest concentration of arsenic in rice that I can detect with the test kit? ___________

6. Which is larger (a) the number of 25-mg grains of rice in a billion kg of rice or (b) the number of atoms in 1 ng of lead? ___________