Chapter 13 Water and Its Solutions

Chapter 13 Water and Its Solutions

Surface Tension

• The net force acting on the molecules on the surface of some liquids due to the cohesive forces of the molecules

• Water has a high surface tension

Freezing and Boiling Points

• The temperature at which a substances freezes

• The temperature at which a substance boils• Water has a high freezing point and high

boiling point

Specific Heat

• The energy required to raise the temperature of 1 gram of a substance 1 °C

• Water has a high specific heat

Density

• Mass/volume• Water is unusual because it is less dense when

it freezes

Solubility• The ability for a substance (solute) to dissolve

in another substance (solvent)

• Solvent – used to dissolve another substance; water is the universal solvent

• Solute – the substance that is being dissolved

Factors that affect solubility

• Stirring (agitation)

• Temperature (Solubility and Temperature)

• Surface area (particle size)– Spoon of granulate sugar vs. cube of sugar

Solubility is

The ability for a substance (solute) to dissolve in another substance (solvent)

Solubility is expressed in mass per volume

Saturated Solution

• A solution containing the maximum amount of solute for a given amount of solvent at constant temperature and pressure

Supersaturated Solution

• A solution that contains more solute than it can theoretically hold at a given temperature

• Excess solute precipitates out of solution

Unsaturated Solution

• A solution that contains less solute than a saturated solution at a given temperature and pressure

How can you make a saturated solution unsaturated?

Add more solvent; Add more water; dilute the solution

How can you make a saturated solution supersaturated?

• Add more solute

Solubility Curve

1. How many grams of KCl can be dissolved at 40°C?

Solubility Curve

2. How many grams of KCl can be dissolved at 80°C?

Solubility Curve

3. At 10°C, 20 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

Solubility Curve

4. At 10°C, 30 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

Solubility Curve

5. At 10°C, 50 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

Solubility Curve

6. Using your answer from #5, how many grams of KCl will settle to the bottom?

Solubility Curve

7. At 10°C, how many grams of KCl are need to make a saturated solution in 200 grams of water?

Solubility Curve

8. At 10°C, how many grams of KCl are need to make a saturated solution in 300 grams of water?

1. Generally as the temperature increase the amount of solute ________________

2. What is the amount of solute of NH4Cl added at 70 o C? __________________

3. What is the amount of solute NaNO3 at 40 o C? ____________________

4. NH3 solubility decreases as temperature increases. What is the amount of grams of solute at 90 o C? _____________________

5. Which solute has the highest solubility at 10 o C? _____________

6. Which solute has the lowest solubility at 10 o C? _______________

7. Of all the solutes on this graph, which solute is not greatly affected by temperature? _____________________

8. Which salt is least soluble in water at 20°C?9. How many grams of potassium chloride can

be dissolved in 200 g of water at 80° C?

10.At 40°c, how much potassium nitrate can be dissolved in 300 g of water?

11.Which salt shows the least change in solubility from 0-100°C ?

12.At 30° C,90 g of sodium nitrate is dissolved in 100g of water. Is this solution saturated, unsaturated, or supersaturated?

Molarity

• A measure of the "strength" of a solution. • A solution that we would call "strong" would

have a higher molarity than one that we would call "weak."

# of moles of soluteMolarity = ---------------------- Liters of solution

• The unit for molarity is M and is read as "molar." (i.e. 3 M = three molar)

Use the trick to solve for the variables.

moles

M Liters

Solve for Molarity

• What is the molarity of a 5.00 liter solution that was made with 10.0 moles of KBr ?

Solve for Volume

What would be the volume of a 2.00 M solution made with 6.00 moles of LiF?

Solve for Volume

Solve for molesIII. Basic molarity problems where the number of moles/grams of solute is the

unknown.

• How many moles of CaCl2 would be used in the making of 0.500 L of a 5.0M solution?

Use the trick to solve for the variables.

moles

M Liters

IV. Given grams instead of molesConvert grams to moles

• mass given# of moles = ----------------- Molar mass

Solve for Volume (and convert to moles)

What is the volume of 3.0 M solution of NaCl made with 526 g of solute?

Convert to molesSolution: First find the molar mass of NaCl.Na = 23.0 g x 1 = 23.0 g

Cl = 35.5 g x 1 = 35.5 g =58.5 g

Convert to moles mass of sample

# of moles = ----------------- Molar mass

526 g

# of moles of NaCl = ------------ 58.5 g

Answer: # of moles of NaCl = 8.99 moles

Example 2. What is the volume of 3.0 M solution of NaCl made with 526g of solute?

Solve for moles and then convert to grams

• How many grams of CaCl2 would be used in the making 0.500 L of a 5.0M solution?

• How many grams of NaI would be used to produce a 2.0 M solution with a volume of 1.00 L?