Exercises

1.     LD50 is a designation for the level of dosage required to kill 50% of the test subjects - usually lab rats.  If it takes only .063 grams of arsenic in a 1.0 liter volume to kill 50 % of a sample of test rats, what is the LD50 for arsenic in parts per million? (A:  63 ppm)

0.063 g*1000mg/g = 63 mg

Ppm = mg/L = 63 mg/1.0 L = 63 ppm

2.     A water purifier claims that it removes 95% of the lead ions from your drinking water.  If your water normally carries .125 grams per liter of lead, what would be the concentration in ppm found in a glass of water you might drink from?  (A:  6.2 ppm)

0.125 g/L *1000mg/g = 125 mg/L

If the filter removes 95% of the lead, then you will be left with 5%.

0.05(125 mg/L) = 6.25 mg/L = 6.25 ppm

3.     If an adrenaline rush can be experienced when your blood contains only 5.4 ppm of the hormone, what total mass of adrenaline is required in the blood of a person who has 6.5 liters of blood total for the hormone to kick in?  (A:  35.1 mg)

Mass = CV

= 5.4mg/L(6.5 L) = 35.1 mg

4.  A tanker of mercury (I) chloride, HgCl, carrying 150 000 kg crashes off the Washington coast.  What total volume of sea water must the cargo mix with to dilute it down below the threshold of 4 ppm?  (A:  3.75 x 1010 L)

note that 150 000 kg *1000g/kg*1000mg/g = 150 000 000 000 mg

M = CV;

150 000 000 000 mg = 4V

V = : 3.75 x 1010 L

Flashback (other types of concentration)

5.         What volume of solution is needed to dissolve 2.0 g of salt in order to create a 0.20 g/L solution?                10 L

6.         What is the concentration in g/L of a 2.0 ppm solution of Cu+2?

0.002g/L