1.1 What is Chemistry?

http://www.ck12.org Chapter 16. Solutions

Lesson Summary

• The concentration of a solution can be expressed as the amount of solute present in a given amount of solvent
  or solution.


• The most common way to express the concentration of a solution is molarity, which is equal to moles of solute
  per liter of solution.


• Another way to express concentration is molality, which is equal to moles of solute per kilogram of solvent.


• The ratio of solute mass to solution mass, when expressed as a percentage, is known as weight percent.


• The ratio of solute particles to the total number of particles in a solution can be expressed in units of parts per
  million (ppm) or parts per billion (ppb).


• Concentrated solutions can be diluted by adding pure solvent. The concentration and volume of the initial
  solution are related to the new concentration and new volume by the equation M 1 V 1 = M 2 V 2.

Lesson Review Questions

1. You have 3.50 L of a solution that contains 90.0 g of sodium chloride (NaCl). What is the molarity of the
   solution?


2. You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain?


3. We want to make 125 mL of a 0.154 M NaCl solution. How many grams of NaCl are needed?


4. A stock bottle of concentrated hydrochloric acid is a 37% (w/w) HCl solution. What is the molarity of this
   solution? How many moles of HCl are in a 10 mL sample of this concentrated acid? The density of 37% HCl
   is 1.19 g/mL.


5. To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a
   reactant. Available to you is 5 L of a 6.0 M K 2 CrO 4 solution. What volume of the solution is required to give
   you the 23.4 g K 2 CrO 4 needed for the reaction?


6. 5.85 g of potassium iodide (KI) is dissolved in enough water to make 0.125 L of solution. What is the molarity
   of this solution?


7. How many moles of H 2 SO 4 are present in 0.500 L of a 0.150 M H 2 SO 4 solution?


8. Calculate the molality of a solution in which 22.0 grams of KBr is dissolved in 250.0 mL of pure water.


9. What is the molality when 0.75 mol of a substance is dissolved in 2.50 L of water?


10. You have 1.00 L of water. How many grams of sucrose would need to be added in order to make a 1.0 molal
    solution?


11. Isopropyl alcohol is typically sold as a 70% (w/w) solution in water. What is the molarity of such a solution?
    Assume that the density of 70% (w/w) isopropyl alcohol is 0.786 g/mL.


12. If a solution contains Pb^2 +ions at a concentration of 15.0 ppm, what would the molarity of this solution be?


13. The presence of sodium fluoride in drinking water at the level of 2 ppm may cause mottled enamel in teeth,
    skeletal fluorosis, and may be associated with cancer and other diseases. Calculate the molarity of a 2 ppm
    solution of sodium fluoride.


14. You want to make 500. mL of 0.050 M HCl by diluting a 6.0 M HCl solution. How much of the concentrated
    HCl solution is needed?

Further Reading / Supplemental Links

• Making solutions: http://www.science-projects.com/solutions.htm