1. Unit 9 Water, Solutions & Reaction Rates
Ch 15, 16 and 18
Chemistry

2. Chapter 15: WATER
The main information and notes for Goals 1 & 2 are found on the Ch 15 Work Sheet. Complete this worksheet and read through Chapter 15.

3. Why does Water have the Properties it does?
Demo #1
Demo #2
Ice Crystal Structure:

4. Liquid Water and Its Properties
Many of water’s special properties can be attributed to its ability to hydrogen bond.

5. Surface Tension Inward force that tends to minimize surface area
Hydrogen bonding increases the inward force, H2O is more attracted to itself than the air molecules, leading to a spherical shape

6. Surface Tension

7. Liquid Water vs. Solid Water
Solid water is less dense than liquid water
Hydrogen bonds force water molecules into a rigid framework as kinetic energy decreases (solid water), leading to a structure with a larger volume than when kinetic energy is higher and water molecules are allowed to slide past one another (liquid water)

8. Aqueous Solutions
Solution – mixture consisting of a solute and a solvent
Solute – dissolved particles
Solvent – dissolving medium
Aqueous Solution – solution in which the solvent is water

9. Solvation Process by which a solute dissolves: Demo
Solvent has to be attracted to solute for solvation to occur (figure 15.8)
If solute is more attracted to itself rather than the solvent, solvation will not occur and the solute is said to be insoluble
“Like dissolves like” is a good rule of thumb to tell whether or not a solute will dissolve in a solvent, in other words solutes and solvents with similar polarities will make a solution

10. Solvation Demo δ+ H attracts Cl- ions δ- O attracts Na+ ions
A similar scheme can be used to illustrate the dissolution of a molecular substance in water.
“Like dissolves like”
Demo

11. Solution Types Miscible: Immiscible: Alloy:
When 2 liquids form a solution they are said to be Miscible.
Liquid/Liquid solutions don’t really have a solute and solvent
They can dissolve in each other in any amount.
Examples:
Water and Vinegar
Water and Alcohol
Immiscible:
When 2 liquids do not form a solution. NOT Miscible
Ex. Water and Oil
Alloy:
Solution of 2 or more solids

12. Mixture Categories

13. Electrolyte
Compound that will conduct an electric current in aqueous solution or the molten state
Ionic compounds are electrolytes because they have a positive and negative charge that can conduct an electric current
Electrolytes can be classified as strong or weak depending on the extent to which the ions dissociate in solution
Non-electrolyte
Compound that will not conduct electricity in aqueous solution or the molten state
Many molecular compounds are nonelectrolytes (compounds of carbon especially)
(see table 17.3 for examples)

14. 16.1 Factors Affecting Solution Process
Stirring – increases rate of contact between solvent and solute
Increase in temperature – increases kinetic energy, leading to an increase in the rate of contact between solvent and solute
Increase in surface area – increases the surface contact between solvent and solute

15. Solubility
Amount of solute that can be dissolved in a quantity of solvent at a given temperature
If a solid solute can be dissolved in a liquid solvent then the solute is soluble, if it can’t be dissolved the solute is insoluble
Represents a Saturated Solution.
Usually expressed as _____g solute/100g Water.
Is effected mostly by Temperature in solid solutes
Is effected by Temperature and Pressure in gas solutes.

16. Solutions Saturated Solution: Unsaturated Solution:
contains the maximum amount of solute particles that can be dissolved in a given quantity of solvent at a constant temperature
Unsaturated Solution:
contains less than the maximum amount of solute particles that can be dissolved in a given quantity of solvent at a constant temperature
Supersaturated Solution: DEMO
contains more than the maximum amount of solute particles that can be dissolved in a given quantity of solvent at a constant temperature
Difficult to create and Usually unstable.
Not all Solute/Solvent Combinations can result in a Supersaturated Solution
DEMO: Sodium acetate in water (50g to 5 mL)

17. Factors affection Solubility: SOLIDS
Solubility of a solid solute generally increase with temperature
Increase in Temperature  Increases Solubility

18. Factors affecting Solubility: Gases
Solubility of a gaseous solute decreases with temperature, but increases with pressure
Increase in Temperature  Decreases Solubility
Increase in Pressure  Increases Solubility

19. 16.2 Concentration of Solutions
The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent.
Molarity (M) = moles of solute/Volume of solution
M = n/V
Units: Moles/Liter
The volume is the TOTAL volume of the Solution, NOT the volume of solvent
Molarity Example:
What is the molarity of a 2.0 L solution containing 4.0 mol NaCl?

20. Making Dilutions Dilution Example
Dilutions are used to make less concentrated solutions by increasing the volume of solvent.
When making a dilution the number of moles of solute stays CONSTANT.
Moles of solute = molarity (M) x liters of solution (V)
M1V1 = M2V2
Dilution Example
How many milliliters of 5.0 M CuSO4 would be needed to prepare ml of 0.50 M CuSO4?

21. Example Problems:
How many moles of HCl must be added to make 2.0L of a 6.0 Molar Solution of HCl (aq)
What is the molarity of a solution if enough water is added to 35g of KNO3 to make 550mL of solution?
How much water must to added to 250mL of 2.0 M KCl to produce 0.75 M KCl?

22. Percent Solutions Percent Volume Example Percent Mass Example
% by Volume: Used only in Liquid/Liquid Solutions
%(v/v) = volume solute / volume solution
Units: Volumes must be in same units
% by Mass: Used in Aqueous Solutions
%(m/v) = mass solute / volume solution
Units: g/mL
Percent Volume Example
What is the percent volume of acetone in water if 25 ml of acetone is added to 75 ml of water?
Percent Mass Example
What is the % (m/v) of a 100 ml aqueous solution containing 10 g of NaCl?

23. Example Problems:
Calculate the Molarity if 25.0g of NaCl is dissolved in enough water to make 750mL of NaCl (aq)
Calculate the %Mass concentration of the solution above.
Calculate the %Volume when 25mL of Vinegar (C2H4O2) is mixed with 125mL of water

24. 18.1 Rates of Reaction Describing Reaction Rates
Rate – measure of how much something changes within an interval of time
EX: 5 mi/hr, 10 m/s, 20 truck loads/day
Reaction Rate – change in the amount of a reactant or product per unit of time. “How fast a reaction occurs”

25. Rate Example
10.0 kg of CO2 (g) are produced by the combustion of fossil fuels at a coal burning power plant in one day. What is the rate of CO2 (g) formation in kg/hr?

26. Continued…
Reactant Depletion or Product Formation must be monitored in order to determine the rate of a chemical reaction.
Things to Measure:
Depletion of a solid reactant
Formation of a precipitate
Formation of a gas
Other factors can be measured to determine the rate of a reaction, but require more complicated procedures.

27. Collision Theory
Collision Theory – atoms, ions, and molecules can react to form products when they collide, if the particles have enough kinetic energy
An effective collision between reactants will form products
An ineffective collision between reactants will produce no reaction
Demo

28. Activation Energy
Minimum amount of energy that particles need in order to react
Essentially a barrier that reactants must cross in order to become products
If there is sufficient energy present and the atoms are oriented properly, they will form an activated complex at the peak of the activation-energy barrier
The activated complex, sometimes called the transition state, will then either form products or re-form into reactants again

29. Catalyst
Substance that increases the rate of reaction without being used up in the reaction itself
Permits reaction to proceed at a lower energy than is normally required
Catalysts lower the activation-energy barrier
A substance called an inhibitor interferes with the action of a catalyst
Enzymes act as catalysts in our body

30. Energy Diagrams
Draw energy diagrams labeling Activation Energy & ΔH for:
Endothermic
Exothermic
With catalyst
Without catalyst

31. Factors Affecting Reaction Rates
Every reaction proceeds at its own rate. However, reaction conditions may be varied in order to either speed up or slow down the rate of a chemical reaction.
Temperature
Concentration
Particle size
Catalyst

32. Temperature
Generally speeds up a reaction by providing particles with more kinetic energy
Collision frequency is increased
Number of particles with enough energy to overcome activation-energy barrier is increased

33. Concentration
Number of reacting particles in a given volume affects the rate at which a reaction occurs
Increasing the number of particles in a given volume will increase the collision frequency
An increased collision frequency leads to an increase in effective collisions and an increased reaction rate

34. Particle Size
Smaller particle size leads to a larger overall surface area
An increase in surface area increases the amount of reactant exposed for reaction
Increased surface area increases collision frequency