Review Questions for Environmental Analysis

For this course you will need to know how to do basic chemical calculations. These require only simple algebra skills and some careful thought. Some of the calculations may require several steps to the final solution, but the individual steps are still simple. Look at the problems on this sheet. If they seem trivial to you, then you should be well prepared for the class. If the problems seem challenging, then you should do them all, for practice. If you get stuck, consult a general chemistry textbook, or  ask for help from me in class or by email. Answers are posted but you should chew on the questions for a while before you peek!

1. You dissolved 0.0142 g of KCl in a 100 ml volumetric flask and diluted to the mark. Then you took 1.00 ml of that solution in a pipet and transferred it to another 100 ml volumetric flask, and filled that to the mark with water. What is the concentration of chloride in the last solution, expressed in moles per liter (M) and in ppm by weight.
2. To make 100 ml of standard containing 0.0100 g of lead/ml how much Pb(NO₃)₂would you weigh out?
3. To make 100 ml of solution containing 1.00 m g lead/ml how much Pb(NO₃)₂ do you need? Can you weigh that amount accurately? How would you make the solution accurately using only 100 ml volumetric flasks and a pipet?
4. A standard solution containing 5.0 ppm of copper gives a reading of 1.94 on an instrument. A water sample gives 1.02. What is the concentration of copper in the water. What are you assuming in doing this calculation??
5. A 1.0 liter water sample is poured through an ion-exchange filter pad which efficiently absorbs copper ions. Acid is used to wash out the copper. The acid wash is collected, diluted to exactly 25.00 ml and is analyzed for copper. The copper concentration in the solution is found to be 4.8 ppm. What was the concentration of copper in the original water sample? (in ppm)
6. How many cubic meters of air are drawn through a sampler in 24 hours if the flow rate is 8.0 liters/min?
7. If 10 m g of lead are trapped on a filter which was installed in the air sampler mentioned above, and run for 24 hours, what is the concentration of lead in the air in (g/m³)?
8. The filter from Problem 7 is extracted with acid and the acid is diluted to 25.00 ml. The acid is found to contain 5.0 ppm of copper. What was the concentration of copper (in g/m³) in the air?
9. A sample of water based paint weighs 3.326 g. When it is dried and reweighed it weighs 1.003 g. What is the percentage of volatiles in the paint by weight? If the paint contains a ratio of 2.45g water to 0.124 g volatile organics, what is the overall composition of the paint? (% solids?, % volatile organics, %water?)
10. I take a sample solution and analyze it for iron and obtain a reading on a spectrometer of 23.4. Then I take 10.00 ml of the same sample and add 10.00 ml of 1.5 ppm iron solution. The new mixture gives a reading of 24.9. Assuming that the readings are directly proportional to the concentration of iron in the solution, what was the concentration of iron in the original sample in ppm??
11. Air is drawn through an impinger containing a solution of base to collect acid gases. Then the remaining base is titrated with acid, and the unreacted amount of base is calculated. From the following data determine the amount of acid in the air sample in moles of H⁺ per 10⁶ mole of air (ppm).