Lecture 1

Question 1

Molarity (M)

Answer 1

moles of solute/L of solution (solv + solt)

Question 2

Mass Percent

Answer 2

• Percent by mass of the solute in solution

Mass % = (mass solute/mass of solution) x 100

Question 3

Mole Fraction (χ)

Answer 3

• ratio of # of moles of component A over # of moles of solution (A + B)
  –> #mol of solute/ #mol solution (solv + solt)

Mole Fraction (A) = χ(A) = nA/(nA + nB)

*for 2 component solution

Question 4

Molality (m)

Answer 4

moles of solute/kilograms of solvent

Question 5

Out of the units of concentration, which is dependent on temperature and why?
- Molarity
- Molality
- Mole fraction
- Mass percent

Answer 5

Molarity
–> M = moles of solute/litres of solution
–> dependent on temperature because volume varies with temp! (M is the only one that takes volume into account)
(ex: holding a pipette in the middle can cause it to expand cuz of heat)

Question 6

What are the steps in the formation of a solution? (3)

Answer 6

1. Overcome intermolecular forces in SOLUTE and expand it (endo step)
2. Overcome intermolecular forces in SOLVENT and expand it (endo step)
3. Allow solute and solvent to mix (exo step)

Question 7

What are the intermolecular forces?

Answer 7

1. London Dispersion Forces (LDF)
2. Dipole-Dipole
   Hydrogen Bonding (stronger D-D force)

Question 8

What are dipole-dipole forces?

Answer 8

Forces between 2 polar molecules when the + and - ends line up close to each other

Line up to:
Maximize +-
Minimize ++, –

Question 9

What is hydrogen bonding?

Answer 9

Very strong type of dipole-dipole force
–> H is bound to F,O,N

TRICK! make sure to draw the molecule to see which atom the hydrogen is bound to

Question 10

What are London Dispersion Forces (LDF)?

Answer 10

Forces that exist between nonpolar molecules
–> temporary dipole moment (e- cloud gets shifted to one side (for a moment))
–> happens since e- are continuously in movement so one side sometimes becomes denser than the other (nonsymmetrical distribution of charge)
–> RESULT: short-lived dipole

ALL molecules have LDF