CHEM 120 Lecture Notes - Lecture 16: Lake Nyos, Colligative Properties, Supersaturation
15 Jun 2018
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CHEM 120: SOLUBILITY OF GASES
Hey’s Law: do the polling questions
&
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- Gases are more soluble in water as P
- More gases are less soluble in water as T
o In organic salts the reverse if often true
- Law fails if the gas reacts with water, therefore can not be used for acids
High pressures, solubility
- Opening a bottle relieves the P, so solubility
- CO2 evaporates from solution as fizz (coke goes flatter (faster) at higher T)
o E.g. deep sea divers breathe high P air under water
o Excess N2 dissolves in the blood, when the diver comes back to the Patm, N2 diffused out
of the blood
▪ Because of this, divers change to helium and oxygen mix
Lake Nyos → lake became supersaturated with CO2, it up-turned and the CO2 was released by 300 000
tons (1 km3 of gas)
- Since CO2 is heavier than air, it displaced all the O2
Colligative Properties: properties are independent of the chemical identity of the solute and depend on
amounts of solute and solvent (conductive, water shell) → third category
- Electrolytes: separate into ions when it dissolves (ionic compounds)
- Non-electrolytes: does not dissociate to form ions (molecules)
- Extensive properties: depends on the quantity of matter (atoms), volume and mass
o Intensive: independent of quantity of matter, density and T
Raoult’s Law: does not work with non-ideal solutions, there are deviations, involves non-volatile solutes
whose Pvap is negligible
- More energy for liquids to go into the liquid phase
- Less sites where vapour will be released
- Pure solution is at equilibrium when Pvap = Pext *** recall
The Pvap of a solution contains both solute and solvent
- The presence in of each volatile component lowers the Pvap of the other since each one lowers
the mole fraction of the other
- PT is geate tha pedited y Raoult’s Law whe Foe A-B < Force A-A & Force B-B
- PT is less than predicted when Force A-B > Force A-A & Force B-B
Binary Liquids:
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Document Summary
He(cid:374)(cid:396)y"s law: do the polling questions (cid:4666)1 1 (cid:4667)] (cid:1845)(cid:1853)(cid:1871)=(cid:3028) & = [ (cid:3042)(cid:3039) Gases are more soluble in water as p . More gases are less soluble in water as t . Opening a bottle relieves the p, so solubility . In organic salts the reverse if often true. Law fails if the gas reacts with water, therefore can not be used for acids. Lake nyos lake became supersaturated with co2, it up-turned and the co2 was released by 300 000 tons (1 km3 of gas) Since co2 is heavier than air, it displaced all the o2. Colligative properties: properties are independent of the chemical identity of the solute and depend on amounts of solute and solvent (conductive, water shell) third category. Electrolytes: separate into ions when it dissolves (ionic compounds) Non-electrolytes: does not dissociate to form ions (molecules) Extensive properties: depends on the quantity of matter (atoms), volume and mass.
