Solutions Molarity

Complete each of the following sentences by filling in the appropriate word or phrase from the list below.

Concentration saturated

Molarity unsaturated

Molality supersaturated

Mole fraction

  1. ____Molarity___ is the concentration of a solution expressed as the number of moles of solute dissolved in each liter of solution.
  2. A ______saturated____ solution contains as much solute as can possibly be dissolved under existing conditions of temperature and pressure.
  3. The amount of solute in a given amount of solvent or solution is the ___concentration__ of a solution.
  4. A solution that contains more solute particles than are needed to form a saturated solution is ___supersaturated__.
  5. The __mole fraction_ is the number of moles of one component of a solution divided by the total number of moles in the solution.
  6. The ____molality____ of a solution is the number of moles of solute that can be dissolved in each kilogram of solvent.
  7. A solution that has less than the maximum amount of solute that can be dissolved is called a(n) ____unsaturated____ solution.

Solve each of the following problems as directed. Show all your work.

  1. What is the molarity of the solution formed by mixing 0.20 mol of sodium hydroxide (NaOH) with enough water to make 150mL of solution?

150mL x 1 Liter = 0.150 L

1000 mL

0.20 mole = 1.33 M

0.150 L

  1. How much potassium bromide (KBr), in grams, should be added to water to prepare 0.50L of solution with a molarity of .0125M?

0.50 L x 0.0125 mole = 0.00625 mole

L

0.00625 mole KBr x 119 g = 0.744g

mole KBr

  1. What is the molality of an alloy containing 0.03g of silver and 4.75g of iron?

1) 0.03g x 1 mole = 0.000278 mole

107.9 g

2) 4.75g x 1 kg = 0.00475 kg

1000g

3) 0.000278 mole = 0.0582 m

0.00475 kg

  1. The molality of a solution of chlorine and water is 0.0362m. This solution contains 3500g of water. How much chlorine, in grams, was used to prepare this solution?

1) 3.500 kg x 0.0362 mole = 0.1267 moles

kg

2) 0.1267 moles x 35.45 g = 4.49g

mole

Answer each of the following questions in the space provided.

  1. Describe how a chemist can accurately prepare a solution of precise molarity.

Measure the grams of a solute.

Divide by the molar mass to determine the number of moles.

Then add the solute to 1 liter of solvent.

  1. How is molality different from molarity?

Molarity = moles

liter

Molality = moles

kg

  1. Explain the importance of knowing the concentrations of solutions in chemical labs and in daily life.

If you don’t know the concentration, you don’t know how much stuff you are adding.