Unit 12 WATER and SOLUTIONS!!!

I.Intermolecular Forces

Most of the properties and characteristics of molecular compounds, including water, come from some combination of intermolecular forces (pg. 463-465).

Name the two types of intra forces we have focused on so far?

1)Dispersion forces:

a.What is it?

  1. Who does it?
  2. How do you make it stronger?

2)Dipole interactions:

a.What is it?

  1. Who does it?

3)Hydrogen bonding:

a.What is it?

  1. Who does it?

What happens as intermolecular forces (both in strength and number) increase?

  1. Cool things about water(pg. 476-481)

Water has some very unique properties. Many are related to the types of intermolecular forces between water molecules. What intermolecular forces are present in a sample of water?

1)Surface tension

a.What is it and what causes it?

  1. What does a surfactant do?

2)Low vapor pressure

  1. What is vapor pressure?
  1. Why is it important that water has a low VP?

3)Heat Capacity

  1. Why is it important water has a high heat capacity

4)“High” melting and boiling points

  1. What causes water’s relatively high melting and boiling points

5)Structure of ice

  1. What is unique about the structure of ice?
  1. What would be an implication if this wasn’t true?

6)Electrolyte vs. nonelectrolyte (pg. 483-485)

  1. What’s the difference?
  1. Why do some solutions conduct and some don’t?

7)Hydrated crystals (pg. 485-487)

  1. Where is the water in a hydrated crystal?
  2. How do you get rid of the water?

8)Colligative Properties

  1. What are the three Colligative properties and define each (pg. 517-519)
  1. Suspensions, Colloids and Solutions

1)Define each and note the differences between the three (pg. 490-493)

Suspensions

Colloids

Solutions

  1. Let’s talk about solutions a bit more in depth

1)A solution is made of two parts, name them and define each (pg. 482)

2)Describe the solvation process (pg. 483)

3)What kind of things dissolve in water (sometimes called the universal solvent)?

4)What does “like dissolves like” mean?

5)What are some things that determine how fast a solute will dissolve in a solvent (pg. 501,502)

6)Solubility (pg. 502-507)

  1. What are the three levels of solubility and describe each.
  1. What is the most common factor that changes solubility?
  2. How does this factor usually effect how solids dissolve in water?
  1. How does this factor usually effect how gases dissolve in water?
  1. Solubility curves

Typical solubility curve questions:

- What is the solubility of KBr at 70o?

- How much KNO3 will dissolve in 75 g of water at 20o, at 80o?

- What happens when 100 g of NaNO3 is added to 100 mL of boiling water, what happens when this is cooled to 50o, what happens when it is cooled to 0o?

V. Concentration Units:

1)Molarity (M) = moles of solute/ L of solution (pg.509-513)

  1. From a solid: What is the M of a solution of 10 g of NaCl in enough water to make 250 mL of solution?
  1. Dilution: (M1V1 = M2V2) I take 25.0 mL of 12M HCl and dilute it to 500 mL with water, what is the solutions new M?

How do I make 250.0 mL of 1.0M nitric acid from a stock solution (15M)?

2)Molality (m) = moles solute/ kg of solvent (don’t forget DH2O = 1 g/mL) (pg. 520)

What is the m of a solution of 56.7 g of calcium phosphate in 500 mL of water?

3)Mole Fraction () = moles component/ total number of moles of solution (pg. 521)

What is the Xsolute of 10 g of NaCl dissolved in 25.0 g of water?

4)Percentages: (pg. 513-514)

  1. Percent by mass = mass solute/ total mass
  2. Percent by volume = volume of solute/ total volume of solution
  3. Percent mass/volume = mass of solute/ total volume of solution

Summary Problem: I dissolved 25.0 mL of C2H5OH (D = 0.82 g/mL) in 75.0 mL of water. The resulting solution had a volume of 97.0 mL. Give the concentration of this solution in all 6 units we’ve learned.

VI. Colligative Properties (defined earlier, but let’s do math! pg.522-524)

1)Boiling point elevation Tb = (kb)(m)

2)Freezing point depressionTf = (kf)(m)

Summary Problem: What are the boiling and freezing points of a 50% by mass solution of water and ethylene glycol (C2H4(OH)2)

We can also use this fp and bp depression data to find the molecular mass of something

(Note sample problem 18-10 on pg. 524, 525)