Solids & Solutions

Question 1

What is molarity?

Answer 1

M = moles solute / Liters solution

• One of the five concentration units

Question 2

What is mass percent?

Answer 2

% = grams solute / grams solution * 100

Question 3

What is mole fraction?

Answer 3

χ = moles solute / moles solution

• All the mole fractions should add up to 1

Question 4

What is molality?

Answer 4

m = moles solute / kg solvent

• Independent of Temperature, unlike molarity

Question 5

What is parts per million?

Answer 5

ppm = grams solute / grams solvent * 1,0000

or ppm = mg solute / kg solution

Question 6

What is benzene?

Answer 6

C₆H₆

Example of a molecular solid, held together by dispersion forces (nonpolar)

Question 7

In what four ways can solids be classified?

Answer 7

1. Ionic
2. Molecular
   
   • Ionic and molecular solids are held together by IMF
3. Metallic
   
   • electrons exist in molecular orbitals that are delocalized over many atoms, producing an electronic band structure
4. Network
   
   • networks or chains of atoms or molecules held together by covalent bonds
   • diamond, graphite

Question 8

What is the effect of Temperature on semiconductor conductivity?

Answer 8

• Direct: conductivity increases with temperature because more electrons are able to move up to the conduction band

Question 9

Face-centered cubic cell: how many atoms, and how can you calculate the atomic radius?

Answer 9

• 4 atoms
• hypotenuse = 4r

Question 10

Body centered cubic cell: how many atoms are there,

and how can you calculate atomic radius (given density)?

Answer 10

• 2 atoms
• 4r = edge√ 3

Question 11

Primitive cubic cell: how many atoms,

and how can you calculate the atomic radius given the density?

Answer 11

• 1 atom
• 2r = edge

Question 12

How can you calculate overall enthalpy of solution?

Answer 12

• Δ_solutionH = Δ_hydrationH - Δ_latticeH
  
  • Hydration enthalpy is the energy released when bonds are formed between the ions and water molecules (negative)
  • Lattice enthalpy is the energy released when gaseous ions bind to form an ionic solid (negative)
    
    • (Subtract this because you have to break the lattice)

Question 13

How do solute-solvent interactions determine solubility?

Answer 13

• The stronger the attractions between solute and solvent molecules, the greater the solubility
• Like dissolves like
  
  • Substances with similar intermolecular attractive forces tend to be soluble in one another.
    
    • Nonpolar substances are more likely to be soluble in nonpolar solvents
    • Ionic and polar solutes are more likely to be soluble in polar solvents
    • Network solids are not soluble in either polar or nonpolar solvents because of the strong bonding forces within the solid

Question 14

How does pressure affect solubility of a gas?

Answer 14

• The solubility of a gas in any solvent is increased as the pressure of the gas over the solvent increases
• (Whereas the solubilities of solids and liquids are not affected by pressure.)
• Henry’s law

Question 15

What is Henry’s Law?

Answer 15

• The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid
• S_g = K_H * P_g
  
  • Where K_H is Henry’s constant

Question 16

What is Raoult’s Law?

What do positive and negative deviations mean?

Answer 16

• Vapor pressure depression: VP lowers as you increase the mole fraction of a solute
  
  • Multiply pure pressure by the mole fraction of solute
    • P_soln = X_solventP^o_solvent
    • Ptotal = X_AP^o_A + X_BP^o_B …
• Only works for ideal mixtures, where there are no IMFs between the particles
  
  • If there is a positive deviation from Raoult’s law (higher vapor pressure), that’s because molecules are breaking away more easily than they do in the pure liquids. The IMFs are less than they are in the pure liquids.
  • If there is a negative deviation from Raoult’s law, new stronger forces must exist in the mixture than in the original liquids.

Question 17

How does temperature affect solubility for solids vs. gases?

Answer 17

• The solubility of most solid solutes in water increases as the temperature of the solution increases
• Whereas the solubility of gases in water decreases with increasing temperature
  
  • Because more gas escapes from solution

Question 18

What is the van’t Hoff factor?

Answer 18

• i= the number of particles a formula breaks up into

Question 19

What is Boiling Point elevation?

Answer 19

• The addition of a nonvolatile solute causes the boiling point of the solvent to increase (and the freezing point of the solvent to decrease)
• Calculate the change with FIKm
  
  • molality!

Question 20

What is Freezing Point depression?

Answer 20

• The addition of a nonvolatile solute causes the freezing point of the solvent to decrease
• Calculate change with BIKm
  
  • molality!

Question 21

What is Osmotic Pressure elevation?

Answer 21

• The osmotic pressure of a solution is the pressure needed to stop the flow of solvent across a semipermeable membrane
  
  • Increases with concentration of the solute
• Calculate osmotic pressure with PIMRT
  
  • MOLARITY!

Question 22

With the addition of a solute,

what’s elevated and what’s depressed?

Answer 22

• Boiling Point and Osmotic Pressure are elevated
• Freezing Point and Vapor Pressure are depressed

Question 23

What are colligative properties?

Answer 23

• Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute
  
  • Vapor pressure depression, boiling point elevation, freezing point depression, and osmotic pressure elevation

Question 24

What are the 3 ways a reaction rate can be expressed?

Answer 24

• Initial rate of reaction
• Average rate of reaction
• Instantaneous rate of reaction