Solvents, Solutes + Gases in Solution

Question 1

What happens if you half fill a container with gas and liquid and let them equilibriate?

Answer 1

The gas molecules will dissolve into the solution.

The liquid molecules will leave the liquid phase and enter the vapour phase.

This demonstrates that the solubility of the gas, is independent of the volatility of the liquid.

Question 2

What factors affect the solubility of gases?

Answer 2

• partial pressure of the gas
• temperature of liquid/gas
• type of gas
• type of liquid

Question 3

What is Henry’s Law?

Answer 3

The higher the pressure - the more molecules of gas dissolve in the liquid, if temperature remains constant.

Question 4

What is the effect of increasing temperature on the solubility of a gas in solution?

Answer 4

The higher the temperature, the less soluble the gas becomes in solution, provided the pressure stays constant.

Question 5

What is more soluble, CO2 or O2?

Answer 5

CO2 - it equilibriates in the alveolus capillary more rapidly than O2. When diffusion is impaired (eg fibrosis) O2 transfer is greatly affected, more than CO2 transfer.

Question 6

What is more soluble, N2O or N2?

Answer 6

N2O is more soluble.

Eg in pneumothorax using N2O can cause an increase in cavity size because it enters more rapidly than N2 exits.

Question 7

What is an inhalational agent more soluble in, blood or oil?

Answer 7

Oil.

Question 8

How does temperature affect the solubility of gases?

Answer 8

The amount of gas dissolved in a liquid decreases as the temperature increases.

Question 9

How does gas type affect the solubility?

Answer 9

CO2 is more soluble than O2

N2O more soluble than N2

Volatiles have different solubilities

Question 10

How does liquid type affect the solubility of gases?

Answer 10

Solubility varies with type of liquid. Volatiles more soluble in oil than blood.

Question 11

What is the solubility coefficient?

Answer 11

It is the volume of gas that dissolves in a given volume of liquid.

Eg. (at 37C and 100kPa) the volume of N2O that dissolves in 1L of blood is 0.47L

= solubility coefficient = 0.47 L

Question 12

What is the Bunsen solubility coefficient?

Answer 12

The volume of gas corrected to standard temperature and pressure, that dissolves in 1 unit of the liquid at the temperature concerned where the partial pressure of the gas above the liquid is 1 atmosphere.

Only used by scientists, not in anaesthetics. It requires volume of gas to be corrected to standard conditions for temp and pressure.

It is expressed as a volume

Question 13

What is the Ostwald solubility coefficient?

Answer 13

The volume of gas that dissolves in 1 unit volume of liquid at the temperature concerned.

It is not corrected to STP, it is independent of pressure, provided the dissolved volume of gas is measured at ambient pressure.

Expressed as a volume

Question 14

What does one osmole contain?

Answer 14

Avogadro’s number of particles (6.02 x 10²³)

It is the number of particles, rather than size or type, that affects the osmolality and osmolarity.

Question 15

What is the difference between osmolality and osmolarity?

Answer 15

Osmolality is the number of osmoles of solute per kilogram of solvent (Osm/kg)

Osmolarity is the number of osmoles of solute per litre of solution (Osm/L)

These values are very similar usually. Osmolarity avoids the effect of temperature and is therefore preferred for research.

Question 16

What is normal plasma osmolarity?

Answer 16

300 mOsm/L

Question 17

How can plasma osmolarity be estimated?

Answer 17

2(Na+ + K+) + urea + glucose

Sodium and potassium are doubled because each has an associated anion (mainly Cl-) and it’s the number of particles that influence osmolarity

Question 18

What is osmotic pressure?

Answer 18

The pressure that a solution containing particles exerts that is dependent on the number of particles in solution (it’s osmolarity).

Question 19

What are colligative properties?

Answer 19

The four properties of a solution that are dependent on the number of particles in that solution.

As the number of particles in solution (osmolarity) increases:

• osmotic pressure increases
• freezing point decreases
• boiling point increases
• solvent vapour pressure decreases (Raoult’s Law)

Question 20

How do osmometers work?

Answer 20

They exploit the colligative properties to measure osmolarity.

Most osmometers use the freezing point depression to measure osmolarity, but those that use the solvent vapour pressure reduction can use smaller test samples.

Question 21

What is tonicity?

Answer 21

The osmolality due to effective osmoles.

Only particles that are restricted to one compartment influence osmolality, and therefore are effective osmoles. Those that move freely across membranes are termed ineffective osmoles and include glucose, urea and alcohol. These do not contribute to osmotic pressure.

Question 22

Why is 5% glucose consider hypotonic?

Answer 22

Even though it is isosmolar, the glucose does not act as effective osmoles. Therefore glucose enters the cells freely and leaves free H2O to distribute throughout all the body compartments.

Question 23

Are colligative properties influenced by the nature of the solute in a solution?

Answer 23

No, they’re influenced by the number of particles in the solute

Question 24

What is Raoult’s Law?

Answer 24

Depression of the vapour pressure of a solvent is proportional to the molar concentration of the solute.

Question 25

What does adding one mole a substance to 1 kg of water do to the freezing point?

Answer 25

It depresses the freezing point by 1.86 degrees C.