Download - 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?