Chapter 15 Summary

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CHAPTER 15

Toxins in Solution

SUMMARY

KEY TERMS

solution

solvent

solute

homogeneous mixture

heterogeneous mixture

concentration

molarity

molar

saturated solution

Toxins Update

It is easy for toxins to dissolve in and enter our water supply. In fact, it would be challenging to find or create a sample of “pure water”—one that had nothing else in it but H2O molecules. To track the concentrations of different substances in solutions, scientists use moles of solute per liter of solvent. This is also called the molarity of the solution. If you know the molarity of a solution and its volume, you can determine the exact number of grams, moles, or even molecules or ions of a substance in your water sample. Sometimes, toxic substances in solution are tracked in parts per million, or ppm. A solution with a toxic concentration of 1 ppm would have 1 mL of toxic substance per 1000 L of solution.

REVIEW EXERCISES

Question 15.1

1. Why is it useful to know exactly how many moles or grams of contaminant are in a water sample?

Question 15.2

2. Lead is one of the few substances with a zero tolerance level in our drinking water, meaning that there should be no lead at all in our water. Why do you think this is?

Question 15.3

3. Consider a 10 mL water sample from a nearby creek that has a 0.002 M lead (II) nitrate, Pb(NO3)2, concentration.

  1. How many lead ions are in this sample?

  2. How many grams of lead nitrate are in this sample?

  3. How many grams of lead ions are in this sample?

Question 15.4

4. Suppose you measure 100 mL each of 1.0 M NaOH, 1.0 M KCl, and 0.5 M PbCl2 solutions.

  1. Which has the greatest concentration?

  2. Which has the most mass?

  3. Which has the most moles?

  4. Which has the most ions?

Question 15.5

  1. Suppose you need to make a 0.5 M solution of sodium hydroxide, NaOH. Explain step by step how you would go about making this solution.

  2. Do you have to use 1 L of water when you make this solution? Explain your reasoning.

Question 15.6

6. A mass of 47 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.50 M solution. What is the volume of the solution?

Question 15.7

7. Determine the molarity of the solutions created by following each set of directions.

  1. Dissolve 7.30 g NaCl to make 500 mL of solution.

  2. Dissolve 43.84 g NaCl to make 1 L of solution.

  3. Dissolve 25.00 g NaCl to make 1 L of solution.

  4. Dissolve 25.00 g NaCl to make 2 L of solution.

Question 15.8

8. How many grams of magnesium sulfate, MgSO4, do you need to make 100 mL of a 0.1 M solution?