Solution Problems

A. Vocabulary

1 Solution homogeneous mixture

written NaCl(aq) which means NaCl dissolved in water

2 Solute the substance that is being dissolved in a solution.

In chocolate milk, the chocolate is the solute.

3 Solvent the substance that does the dissolving in a solution.

In NaCl(aq), water is the solvent.

4 Solubility the amount of solute that dissolves in a given amount of solvent

at a given temperature. If a substance is soluble, it dissolves in water.

B. Using the Reference Tables

1. Table F Table F tells if a substance dissolves (soluble) or

does not dissolve (insoluble) in water Examples

(NH4)2O All ammonium compounds are soluble

CaS All sulfides are insoluble

AgBr All halides are soluble except with Ag+

Ba(OH)2

All hydroxides are insoluble except Ba+2

2. Table G Reference Table G shows how solubility changes

with temperature Each line represents a compound’s saturation point

On the line Saturated—maximum solute that can dissolve

Below the line Unsaturated—not saturated; can still hold more solute

Above the line “over saturated” Supersaturated (dissolves anyway) Precipitate (excess solute falls to the bottom of container)

Example

30g KClO3 in 100g water at 70 ºC Check mass of water Locate g and temp Locate compound On/below/above the line

Under the line Unsaturated

Example 20g HCl is dissolved in 25g water at 30 ºC

Check mass of water 25g water must be made into 100g Multiply all masses by 4

Locate g and temp 20g →80g 25g → 100g

Locate compound On/below/above the line

Over the line Supersaturated

Example A saturated solution of KNO3 is made using

100g water at 60 ºC. What happens when the solution is cooled to 10 ºC Identify amount to saturate at each temperature

60ºC 105 g

10ºC 25 g

Compare 25g stays dissolved 80g precipitates out

C Expressions of Concentration

Concentration represents the amount of solute dissolved in a solution

1. Vague Terms Strong vs weak Concentrated vs dilute

2. Measured values Molarity ppm (parts per million)

3. Molarity

Represents moles of solute per 1 liter of solution Ex. What is the molarity of a solution containing 1.2 moles

NaCl in a 150 mL solution? M = moles ÷ liters 150 mL = 0.150 L

Move decimal 3 places M = 1.2 ÷ 0.150 L M = 8.0M

Means 8 moles NaCl in 1 liter of solution

4. Parts per Million (ppm)

ppm = grams solute x 1,000,000

grams solution

Ex. 0.0043g of O2 can be dissolved in 100 g water at 20ºC. Express this in terms of parts per million.

ppm = grams solute x 1,000,000 grams solution ppm = 0.0043 x 1,000,000 = 43 ppm 100.0043

Practice Problems

1. What is the molarity of a KF solution containing 0.32 moles in 200 mL of solution?

2. What is the molarity of a NaCl solution containing 1.02 moles in 125 mL of solution?

3. What is the molarity of a NaOH solution containing 12g NaOH in 50 mL of solution?

4. What is the ppm of a CO2 solution containing 0.032 grams in 200g of solution?

5. What is the ppm of a NH3 solution containing 0.0012 grams in 350g of solution?

Dilution Problems

Addition of water to change the concentration Two types

Dilute an amount of solution and determine the new molarity

Determine how much of a concentrated solution must be used to make a specific molarity

Dilute an amount of solution and determine the new molarity

ex. What is the concentration of a solution made if 35 mLs of 18M H2SO4 is diluted to 250 mLs?

Find the original mole value Find new molarity

0.035 L x 18 moles =

1 L

0.63 moles =

0.250 L

0.63 moles H2SO4

2.52 M H2SO4

Determine how much of a concentrated solution must be used to make a specific molarity

ex. How would you make 100 mL of a 3.0M HCl using 12M HCl?

How many moles do you need? Find the volume needed of the concentrated solution

0.100 L x 3.0 moles =

1 L

0.30 moles x 1 L =

12 moles

Use 25 mLs HCl

0.30 moles HCl

0.025 L HCl