Osmometry

Question 1

Molarity

Answer 1

the concentration of a solution expressed as the number of moles of solute per litre of solvent

Question 2

Molality

Answer 2

the concentration of a solution expressed as the number of moles od solute per kilogram of water or solvent

Question 3

Osmole

Answer 3

the amount of a substance that dissociates to produce 1 mole of particles in a solution

Question 4

Osmolarity

Answer 4

the concentration of a solution expressed as the number of osmoles of particles per litre of water

Question 5

Osmolality

Answer 5

the concentration of a solution expressed as the number of osmoles of particles per kilogram of water

Question 6

Colligative properties

Answer 6

the properties of a solution that depend on the number of particles in a solution (osmotic pressure, boiling point, freezing point)

Question 7

Osmometry

Answer 7

a technique for measuring the concentration of dissolved solute particles that contribute to the osmotic pressure of a solution

Question 8

Freezing Point Depression

Answer 8

a phenomenon in which the addition of solute molecules to a solution lowers the temperature at which a solution will freeze

Question 9

What does osmolality assess

Answer 9

renal function and ingestion of toxins

Question 10

What is the relationship between freezing point and osmolality

Answer 10

freezing point decreases 1.86C for each osmole of particles/kg of solution

Question 11

What are the main components of a freezing point osmometer

Answer 11

cooling mechanism, thermistor, a mechanism to initiate freezing and a readout display

Question 12

How does freezing point osmometry work

Answer 12

a small amount of sample is placed in a cooling chamber, the temperature is decreased below the expected freezing point and then a physical shock is applied to initiate the formation of ice crystals. The sample begins to solidify and releases heat, a temperature probe detects a decrease in resistance as the temperature increases. The temperature will increase until it reaches a plateau which is the freezing point

Question 13

How is a freezing point osmometer calibrated

Answer 13

with sodium chloride solutions of known concentrations

Question 14

What are sources of error in freezing point osmometer

Answer 14

• pipetting different sample volumes
• air bubbles in the sample
• preparing samples too early causing evaporation
  -particulate matter may initiate early seeding

Question 15

What are the major osmotically active components of serum

Answer 15

sodium, chloride, bicarbonate, glucose and urea

Question 16

What is the osmolal gap

Answer 16

the difference between the measured osmolality and the calculated osmolality

Question 17

What causes an increased osmolal gap

Answer 17

presence of unmeasured molecules or ions such as ethanol, methanol, isopropanol or ethylene glycol, ketones or mannitol

Question 18

What causes a decreased osmolal gap

Answer 18

lab error

Question 19

What is the equation for calculated osmolality

Answer 19

2Na + glucose + urea

Question 20

What is the equation for osmolal gap

Answer 20

measured osmolality - calculated osmolality

Question 21

What is the equation for unaccounted osmolal gap

Answer 21

measured - [calculated osmolality +1.25 x Ethanol]