Colligative Properties 1+2

Question 1

What is the definition of colligative properties? What does it include?

Answer 1

Physical properties of solutions that are dependent on the NUMBER of dissolved non-volatile solute species

Include

• Vapour pressure lowering
• Boiling point elevation
• Freezing point depression
• Osmotic pressure –> particular significance to pharmacists

Question 2

For the following questions about colligative properties, complete the missing words;

A) When a solute is dissolved in a liquid (eg water) the solvent molecules are …

B) The entropy of the solvent (and the system) has increased so the …

Answer 2

A)

• When a solute is dissolve in a liquid (eg water) the solvent molecules are more disordered than in the pure solvent

B)

• The entropy of the solvent (and the system) has increased, so the solvent will have a lower free energy.
• G = H - T*S (increase in S, decrease in G)
• (G = free energy; H = enthalpy, S=entropy)

Question 3

When a nonvolatile solute is combined with a solvent, what is the vapour above the solution provided by?

Answer 3

The vapour above the solution is provided solely by the solvent

Question 4

Vapour pressure of a solution is lower than that of the solvent

True or False? Explain why.

Answer 4

True –> solvent has lower free energy and needs more energy to vaporise –> solvent has higher vapour pressure

Question 5

Why are the molecules of solvent at the surface replaced with molecules of solute?

Answer 5

It lowers the tendency of solvent molecules to escape

Question 6

What is the reduction in vapor pressure proportional to?

Answer 6

Proportional to the relative number of the solute molecules

Question 7

What does Raoult’s Law state (vapour pressure lowering)? What does the relative vapor pressure lowering depend on?

Answer 7

Raoult’s law states that the vapour pressure, P₁, of a solvent over a dilute solution is equal to the vapour pressure of the pure solvent, p₁^o , multiplied by the mole fraction of solvent in the solution, X1

• P1 = X₁p₁^o

The relative vapour pressure lowering depends only on the mole fraction of the solute.

• see attached image for equation

Question 8

For Boiling Point;

A) It is the temperature at which …

B) Why do solutions boil at a higher temperature?

C) What is its effect proportional to?

D) What happens when a solute is dissolved in a solvent?

Answer 8

A)

• Boiling point is the temperature at which the vapour pressure of the liquid becomes equal to atmospheric pressure

B)

• Because vapour pressure of a solution is lower than that of the solvent, solutions boil at a higher temperature

C)

• The effect is proportional to the number of dissolved species (ie concentration)

D)

• If a solute is dissolved in the solvent, the solution acquires a new boiling-point that is at a higher temperature

Question 9

Provide a graph comparing pressure to temperature for solvent and solutions.

A) Why is the plot for solution shifted to the right? (for any given pressure)

B) How to get solution to boil at same temperature as solvent?

Answer 9

A)

• Need higher temperature for solution to reach boiling point as opposed to solvent because the vapour pressure of the solution is lower

B)

• Decrease pressure

Question 10

For depression of freezing point (melting point);

A) Freezing point of a solvent is the temperature …

B) Freezing point of a solution is the temperature …

C) What is the depression of freezing point proportional to?

Answer 10

A)

• Freezing point of solvent is the temperature at which solid and liquid phases coexist at atmospheric pressure

B)

• The freezing point of a solution is the temperature at which liquid solution is in equilibrium with solid solvent - lower than that of the pure solvent.

C)

• Depression of freezing point is proportional to the number of solute species in solution

Question 11

Provide a graph comparing pressure to temperature of Depression of Freezing Point/Elevation of Boiling Point of Water by a solute

A) For a solution consisting of solute and water, what is the freezing point?

B) Why is vapor pressure shifted to the right?

Answer 11

A)

• Freezing point is lower for any pressure

B)

• Boiling point is higher for solution

Question 12

For Osmosis;

A) Provide a definition

B) What happens if a solution is a separated from a solvent by a semi-permeable membrane

Answer 12

A)

• Substances in solution diffuse from areas of high concentration to areas of lower concentration

B)

• If a solution is separated from a solvent by a semi-permeable membrane (one through which only solvent molecules can pass), then only the solvent molecules can diffuse to equalise concentration (activity) –> solbent molecules goes to the solution side

Question 13

For omsotic pressure;

A) Defined as the passage of the solvent into …

B) What is it?

C) What is it proportional to?

Answer 13

A)

• Osmosis is defined as the passage of the solvent into a solution through a semipermeable membrane

B)

• Osmotic pressure is the pressure which must be applied to a solution to prevent water (solvent) from flowing in via a semipermeable membrane

C)

• Osmotic pressure is proportional to the number of dissolved species in solution.

Question 14

Why is osmotic pressure of interest to pharmacists?

Answer 14

Osmotic pressure is of interest to pharmacists as biological membranes act as (imperfect) semi-permeable membranes

• Undesirable osmotic movement of water through biological membranes may cause serious consequences for patients
• Osmotic effects can also be exploited for therapeutic effect

Question 15

What is the Van’t Hoff Equation

Answer 15

Question 16

What is the Van’t Hoff equation for osmotic pressure?

Answer 16

Question 17

What is the Morse Equation? What is the molality?

Answer 17

Question 18

What is ISO-OSMOTIC or ISOMOTIC? How do non-electrolytes dissociate compared to how ionic species dissociate? What is Osmol?

Answer 18

When two solutions, separated by a semipermeable membrane, each have equal concentrations of dissolved species, no net movement of solvent will occur and the solutions are said to be “ISO-OSMOTIC” or “ISOSMOTIC”.

• Non-electrolytes will dissolve to produce a single species,
• ionic species dissociate to produce two or more species.

> The Osmol is a measurement of the number of dissolved species

Question 19

For Osmols;

A) What is the osmotic pressure proportional to?

B) What is the unit used to measure osmotic concentration?

C) It is the weight of grams in a solute that is …

D) What is the number of osmols of a solute equal to?

E) What is the equation?

F) What does 1mmol of dextrose/glucose (nonelectrolyte) represent?

G) How to work the total number of species in solution for electrolytes

Answer 19

A)

• Osmotic pressure is proportional to the total number of entities in solution.

B)

• The unit used to measure osmotic concentration is the osmole (Osmol), or more commonly, milliosmole (mOsmol).

C)

• Osmol =weight in grams of a solute that is osmotically equivalent to a mole of non-electrolyte

D)

• The number of Osmols of a solute equals the number of moles multiplied by the number of species produced on dissolution.

E)

• Osmol/L = M x no: of dissolved species

F)

• For dextrose/glucise, a nonelectrolyte, 1 mmol represents 1 mOsmol

G)

• For electrolytes, the total number of species in solution depends on the degree of dissociation of the substance in question

G) Depends on the degree of dissociation of the substance (see attached image)

Question 20

Define both osmolality and osmolarity

Answer 20

Osmolality

• Osmolality is defined as the mass of solute that when dissolved in 1 kg of water will exert an osmotic pressure equal to that exerted by a mole of an ideal un-ionised substance dissolved in 1 kg of water.

Osmolarity

• Osmolarity is defined as the mass of solute which, when dissolved in 1 litre of solution, will exert an osmotic pressure equal to that exerted by a mole of an ideal unionised substance dissolved in 1 litre of solution.

Question 21

What happens whenever there is an imbalance in the concentration of dissolved species (to which a biological membrane is impermeable) on either side of the membrane? What does this lead to in the human body?

Answer 21

Whenever there is an imbalance in the concentration of dissolved species (to which a biological membrane is impermeable) on either side of the membrane, water will move through the membrane to correct the imbalance

• These effects can cause temporary or permanent damage to red blood cells, irritation to vascular and ocular tissue, irritation to nasal tissue and interference with cilial action as well as effects on the gastrointestinal mucosa.

Question 22

What does rendering a solution iso-osmotic with a body fluid means? Why are some solutes able to pass through semi-permeable membranes?

Answer 22

Means that it contains the same number of units/volume of solute as the body fluid. In theory, no net passage of water would be expected across the biological membrane.

• BUT, biological membranes are NOT perfect semipermeable membranes and some solutes are able to pass through them

Question 23

What is a isotonic solution?

Answer 23

An isotonic solution is one which results in no net movement of water across the biological membrane

> Two solutions that contained no solute that was able to pass through the membrane –> isotonicity and iso-osmoticity would be the same

> May/may not be exactly the same osmolarity

Question 24

A solution that is iso-osmotic with body fluids may not necessarily be ….? Why so?

Answer 24

A solution that is iso-osmotic with body fluids may not necessarily be isotonic.

• Biological membranes are permeable to some small solutes (eg urea, propylene glycol, ammonium chloride, glycerol). There are some differences in permeability of different membranes (eg rbc permeable to boric acid, but mucous lining of eye is not)

Question 25

Explain the following "a solution that is not isotonic is paratonic (unable to cross membrane)"

Answer 25

* It may be hypotonic (containing a lower concentration of dissolved species) or hypertonic (containing a higher concentration of dissolved species)

Question 26

What happens when RBC is placed in a solution that is hypotonic?

Answer 26

water moves into the cells --\> swelling and lysis of the cells * conc in red blood cells higher than outside

Question 27

What happens when RBC are exposed to a solution that is hypertonic?

Answer 27

Water moves out of the cells--\> shrinking and crenation of the cells. This is reversed when the tonicity of the solution is restored to isotonicity. * concentration outside RBC higher than inside

Question 28

For Intravenous parenteral formulations; A) What is an example of a hypotonic IV infusion? B) What is an example of a hypertonic IV infusion? C) Example of total parenteral nutrition? Is it hyper or hypo tonic?

Answer 28

A) * Hypotonic IV infusions --\> haemolysis and water invasion into other body cells (which can lead to water intoxication – convulsions and oedema - pulmonary, cerebral). Renal failure may develop from haemoglobinaemia. B) * crenation of rbcs * Small volumes administered slowly into fast flowing vein rapidly diluted in blood stream Æ minimal problems. C) * Hypertonic, large volume – administered slowly via central vein * Hypertonic IV given via a vein with slow circulation may also irritate the blood vessel walls Æ occlusion * arge volumes delivered too rapidly can cause osmotic diuresis (Æ dehydration)

Question 29

What is an example of an intrathecal injection? What tonicity is it?

Answer 29

* Paratonic solutions disrupt osmotic pressure --\> headache, vomiting --\> more serious neurological consequences eg seizures * Intrathecal injections must be strictly isotonic --\> injected into CSF

Question 30

What is an example of an intramuscular injection? What tonicity is it?

Answer 30

* Slightly hypertonic encourages dilution by tissue fluids --\> rapid absorption * draw moisture in injection --\> allows the injection to be rapidly diluted

Question 31

What tonicity should nasal installations be?

Answer 31

Nasal Instillations that are not isotonic irritate the nasal mucosa and interfere with cilial action

Question 32

What tonicity should ophthalmic preparations be?

Answer 32

Ophthalmic preparations should usually be isotonic to avoid irritation to the mucous membranes and flushing due to tear formation

Question 33

What tonicity should enteral feedings be? What are some side effects?

Answer 33

* Enteral feeding solutions are hyperosmotic – if excessively hyperosmotic, osmotic diarrhoea and mucosal damage can occur (individual variation in tolerance) \> In premature infants, high tonicity of enteral feeds associated with necrotising enterocolitis

Question 34

What tonicity should oral medications be?

Answer 34

Oral liquid medications are often highly hyperosmotic – when given to premature infants can cause pneumotosis intestinalis * can only reduce the tonicity of a hypertonic solution by dilution

Question 35

Give THREE examples of pharmaceutical preparations that should be isotonic and explain the reasons for this requirement

Question 36

Differentiate between iso-osmoticity and isotonicity

Question 37

Explain how a small volume of a hypertonic injection may be administered safely

Question 38

Describe the problems associated with intravenous infusion of large volumes of hypotonic solutions

Question 39

Briefly describe the FOUR colligative properties of solutions

Question 40

What are two solutions with the same osmotic pressure?

Answer 40

Iso-osmotic with each other and will each contain the same concentration of dissolved species * no net movement of water across membrane

Question 41

How can a hypo-osmotic solution be rendered iso-osmotic?

Answer 41

A hypo-osmotic solution can be rendered isoosmotic with another solution by adding enough solute until the osmotic pressures are equal.

Question 42

How can a hyper-osmotic solution be rendered iso-osmotic?

Answer 42

A hyper-osmotic solution can only be rendered iso-osmotic (with another solution) by dilution

Question 43

All colligative properties depend on the number of dissolved species, why are other colligative properties used to indicate osmotic pressure? What are examples of these other colligative properties?

Answer 43

**Osmotic pressure is not easily measured** * The most readily measurable colligative property is **_FREEZING POINT DEPRESSION_** \> if pass through membrane --\> iso-osmotic solution will not be isotonic \> if can't pass through membrane --\> iso-osmotic solution will be isotonic

Question 44

What is the difference between freezing point and freezing point depression?

Answer 44

The biological fluids, blood plasma and lacrimal fluid, have a freezing point of -0.52^oC (ie freezing point depression (cf water) is 0.52^oC) * freezing point = negative value * freezing point depression = positive value \> Any other aqueous solution that has the same freezing point (-0.52^oC) will have the same osmotic pressure as plasma and tears – iso-osmotic

Question 45

When a solution that is iso-osmotic with biological fluids be isotonic?

Answer 45

A solution that is iso-osmotic with biological fluids will be isotonic **PROVIDED that the biological membrane is not permeable to any of the solutes in the solution**

Question 46

What will an aqueous solution with a freezing point higher than -0.52^_oC be? How to make it isotonic? What drug is used to adjust tonicity in parenteral or opthalmic solutions?

Answer 46

An aqueous solution with a freezing point higher than -0.52^oC will be hypotonic --\> not enough solute species in solution * Such a solution can be rendered isotonic by addition of sufficient solutes to reduce the freezing point to -0.52^oC (provided the membrane is impermeable to all solutes in the solution --\> cant cross membrane) * Sodium chloride or dextrose is used to adjust the tonicity of parenteral solutions * Sodium chloride, boric acid or (occasionally) dextrose is used to adjust ophthalmic solutions

Question 47

Aqueous solutions of 0.9%w/v NaCl (Normal Saline) or 5%w/v Dextrose (D5W) are isotonic * What happens to D5W when administered?

Answer 47

* Once administered, D5W is considered hypotonic as the dextrose is rapidly metabolised --\> water. Used to treat dehydration.

Question 48

A) What is the freezing point of an aqueous solution of 0.9%w/v sodium chloride? B) What would the freezing point of ½ strength NS (0.45% Sodium Chloride) be?

Answer 48

A) -0.52^OC B) -O.26^OC

Question 49

For tonicity adjustment; A) What controls the freezing point B) What happens at low concentrations to the magnitude of freezing point depression C) What exerts a effect on freezing point D) What is the freezing point depression of a solution of mixed solutes?

Answer 49

A) * As the **number** of dissolved species controls freezing point, equal % concentrations of different solutes will have different impacts on freezing point B) * At low concentrations, the magnitude of freezing point depression is proportional to the concentration of a particular solute C) * Each solute exerts its own effect on freezing point, independently of any others present D) * The freezing point depression of a solution of mixed solutes is the total of the freezing point depression caused by each solute.

Question 50

What are isotonicity solutions calculating using freezing point depression/SCE really calculating?

Answer 50

Isotonicity calculations using freezing point depression or SCE are really calculating **iso-osmoticity** * Remember that biological membranes are not perfectly semi-permeable

Question 51

What does the superscript 'a' mean for solutes? Why are these substance left out of the isotonicity calculation?

Answer 51

These substances are usually left out of the isotonicity calculation because they equilibrate on both sides of the membrane. * Eg Propylene Glycol \> Boric acid is an interesting example – it passes through the membrane of red blood cells, but not through the mucous lining of the eye \> It would be included when calculating for isotonicity for eye drops, but not for injections

Question 52

Explain the relationship between osmotic pressure and freezing point depression and explain an application of this relationship

Question 53

Question 54

Propylene glycol has a value for FD1% listed in the APF, yet this value is not included in isotonicity calculations for solutions containing propylene glycol. Explain why.

Question 55

If an aqueous solution of dextrose has a freezing point of -0.87oC, explain how it can be rendered isotonic.