Solubility

Question 1

What phases do liquids in containers always have?

Answer 1

2 phases, a liquid with a vapour phase immediately above.

Usually always has a gas phase also.

Question 2

What is vapour?

Answer 2

A gaseous phase but below its critical temperature and so the addition of pressure can liquidise it.

A vapour can be liquified by the addition of pressure alone, whereas a gas can’t.

Question 3

What is saturated vapour pressure?

Answer 3

The pressure exerted by a vapour at its equilibrium e.g. when the rate of evaporation from the liquid phase matched the rate of condensation from the vapour phase.

(YouTube)

Question 4

What is Henry’s law?

Answer 4

At a given temperature, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in equilibrium with that liquid I.e. higher pressure = more dissolved.

(YouTube)

Question 5

What happens in the bends and what law is this related to?

Answer 5

The rapid drop in pressure allows dissolved nitrogen to rapidly vaporise out of liquid forming bubbles. This fits with Hery’s law.

Question 6

According to Henry’s law, what happens if temperature increases and what does this do to solubility?

Answer 6

More gas will bubble out and so solubility will decrease

Question 7

What is the Bunsen solubility coefficient?

Answer 7

The volume of gas (corrected to standard temp and pressure) in a unit volume of liquid (at any temperature) where the partial pressure of the gas is above one atmosphere.

Question 8

What is the Ostwald solubility coefficient?

Answer 8

The volume of gas dissolved in a unit volume of liquid at the temperature concerned (not corrected to standard temp and pressure).

Question 9

Is the Bunsen or Ostwald solubility coefficient favoured by anaesthetists?

Answer 9

Ostwald as it is not corrected to standard temp and pressure

Question 10

What is the partition coefficient?

Answer 10

It is the ratio of the amount of substance present in one phase compared to another, with both phases of equal volume at equilibrium e.g. a blood gas coefficient.

Question 11

What is the blood gas partition coefficient for N2O

Answer 11

0.46

Question 12

What term do we use for gas in a solution instead of partial pressure?

Answer 12

Tension

Question 13

What is the tension of a gas in a solution?

Answer 13

The partial pressure of the gas in equilibrium with it

Question 14

Do less soluble agents achieve alveolar equilibrium more or less quickly than more soluble and what does this do to their onset?

Answer 14

Less soluble achieve equilibrium more quickly and have a faster onset

Question 15

List from most to least soluble:
N2O, enflurane, Des, halothane, iso, ether, sevo

Answer 15

Ether, halothane, enflurane, iso, sevo, N2O, des. (Xenon)

Question 16

Give the B:G coefficients for:
Des, nitrous, sevo, iso, enflurane, halothane, ether

Answer 16

Des: 0.45
Nitrous: 0.46
Sevo: 0.68
Iso: 1.4
Enflurane: 1.91
Halothane: 2.2
Ether: 12

(Xenon 0.12)

Question 17

Why do we not use nitrous in pneumothorax?

Answer 17

Nitrous is 30 times more soluble than nitrogen, so will diffuse into the nitrogen filled pneumothorax more quickly than nitrogen can diffuse out, meaning it will fill up closed gas filled spaces quickly.