lecture 5

what do u assume

h is independent of temp

colligative properties

Change in other properties only dependent on number of solute
molecules → colligative properties

when are colligative properties valid

Only valid when concentration of solute is low enough to neglect
interactions between molecules

Examples of colligative properties

– Vapor pressure lowering
– Boiling point elevation
– Freezing point depression
– Osmotic pressure

Raoult’s law

does chemical potential water molecules in liquid phase decrease or increase when adding solute

Chemical potential of water molecules in liquid phase decreases
when we add solute

• Water molecules now interact with solute particles too (e.g., via hydrogen bonding or ion-dipole interactions)

• This makes water molecules less free to move or evaporate

👉 So their freedom goes down → chemical potential decreases

We now have 𝜇𝑤,𝑙𝑖𝑞𝑢𝑖𝑑 < 𝜇𝑤,𝑣𝑎𝑝𝑜𝑟

Henry’s Law what do u assume

assume gas dissolves liquid

explain

Amount of dissolved gas increase or decrease with pressure

increase

what is slope of line

what happens when u add solute to liquid phase(freezing point depression)

Add solute to liquid phase
– Further decrease in freezing point

whats the principle of osmosis

semi-permeable membrane

pressure difference= osmotic pressure

what happens when adding solute osmosis

uw is lowered

when do u get eqm with osmosis

Process stops at fluid level where osmotic pressure is balanced by
hydrostatic pressure difference

what happens with smaller molecules in osmosis, or more ions

smaller molecules=more moles= more particles

more ions=more particles=increase osmotic prressure

Does smaller molecules mean higher osmotic pressure?

On a weight basis small molecules are more effective than large
molecules, even more true when they dissociate

describe fruit cooking

Texture of fruit cooked in water vs. concentrated sugar solution
→ big difference
– Cook fruit in sugar solution → shrivels but stays intact
– Cook fruit in water → completely disintegrates
• Difference caused by water transport through osmosis

fluid for patient hydration has to be

Fluids for patient hydration need to be
isotonic

how would u desalt water

Process of osmosis reversed to de-salt seawater
• Apply external pressure → pure water is transported through semi-
permeable membrane leaving salt molecules behind
• Since osmosis is such a strong effect, reversed osmosis is
expensive

rank these :

freezing point depression

osmotic pressure

boiling point elevation

vapor pressure lowering

Osmotic pressure >> Vapor pressure lowering > Freezing
point depression > Boiling point elevation

Only Very Frosty Beverages

does osmotic pressure decrease or increase when dimers/trimers are formed

• When proteins form dimers/trimers, the number of particles decreases (even though the total mass stays the same).

• Fewer particles = lower osmotic pressure.