22012018

Question 1

Osmotic pressure (pi)

Answer 1

• pi = MRT, where R = gas constant, T = temp

Question 2

Van’t Hoff factor (i)

Answer 2

• Ratio btw actual concentration and concentration calculated frm substance by mass
• Change in T_f = iK_fm
• pi = imRT

Question 3

0.05m HCL

Answer 3

• i closes to 2

- Observed i = 1.9

Question 4

Glucose

Answer 4

• Non-electrolyte

> i = 1

Question 5

Dilution

E.g. Reduce concentration from 0.05 M to 0.04 M

Answer 5

• Closer to the expected Van’t Hoff factor (i)

Question 6

(KI): 0.0100M

Calculate the Van’t Hoff factor

Answer 6

- M = pi / (RT)
> M = 0.465 atm / (0.08206 L*atm/K*mol * 298 K)
> M = 0.0190 M
- Calculate Van’t Hoff factor i
> i = 0.0190 M / 0.0100M
> experimentally determined = 1.90
> expect a value 2

Question 7

Use freezing-point pressure to calculate the molar mass

Example: (refer to notes)

Answer 7

• Change in T_f = K_f * m
• Step 1: Figure out the amount of ethanol
  > mass of etOH = 50.0 mL * 0.789 g/mL = 39.5 g = 3.95 * 10^-2 kg
• Step 2: Solve for m
  > m = Change in T_f / K_f = 1.55 C / 1.99 C/m = 0.779 m
  > Meaning: 0.779 mole of quinine per kg of etOH solvent
• Step 3: Calculate amount of quinine
  > (0.779 mol quinine / kg etOH) * (3.95 * 10^-2) = 0.00308 mol quinine
• Step 4: Find molar mass of quinine
  > 10.0g quinine / 0.00308 mol quinine = 325 g/mol

Question 8

Use osmotic pressure to find the molar mass

Example: (refer to notes)

Answer 8

• pi = MRT
  > Rearrange: M = pi / (RT)
  = 1.88 * 10^-2 atm / (0.08206 Latm/Kmol * 298K)
  = 7.69 * 10^-4 M (moles/L)
• Step 2: Figure out molar mass
  > molar mass = 50.0 g / (7.69 * 10^-4 mol) = 6.50 * 10^4 g/mol