Parenteral Tonicity and Colligative Properties

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Questions and Answers

What is the primary factor that drives the movement of solvent molecules across a semi-permeable membrane?

The temperature of the solvent molecules

The osmotic pressure exerted by the solute

The vapour pressure differential across the membrane (correct)

The concentration of solute on both sides of the membrane

Which of the following correctly defines osmotic pressure?

The pressure applied to maintain a specific concentration of solute

The pressure needed to make fluid levels equal on both sides of a membrane (correct)

The pressure measured when a solution is at equilibrium

The pressure needed to increase the solute concentration in the solution

What is the difference between osmolality and tonicity?

Osmolality depends on the solvent, while tonicity depends on the solute concentration

Osmolality is measured in kg of solvent, while tonicity is measured in liters of solution

Osmolality measures total solute, while tonicity measures active solute particles only

Osmolality is specific to a solution, whereas tonicity references a particular membrane (correct)

What is meant by the term 'colligative property'?

Properties that depend on the number of solute particles in a solution Signup and view all the answers

Which of the following statements about osmolarity is correct?

It is measured in osmol per liter of solution Signup and view all the answers

What is the primary difference between tonicity and osmolarity?

Tonicity measures the effect of a solution on cell volume at equilibrium, while osmolarity is a concentration measure. Signup and view all the answers

Which method uses the freezing point of solutions to estimate osmotic pressure?

Freezing point depression (FPD) method Signup and view all the answers

When calculating tonicity, what substance can be added to adjust to plasma levels?

NaCl or dextrose solution Signup and view all the answers

In the concentration method of tonicity calculations, what do you subtract from the standard osmolarity?

The total osmolarity of the formulation Signup and view all the answers

What is the freezing point of a 0.9% w/v NaCl aqueous solution?

-0.52 degrees Celsius Signup and view all the answers

What does the sodium chloride equivalent method determine?

The amount of NaCl that produces the same osmotic effect as a given drug Signup and view all the answers

What is tonicity unable to provide in terms of measurement?

Units for measurement Signup and view all the answers

What unit is osmolarity typically expressed in?

Milliosmoles per liter Signup and view all the answers

Study Notes

Parenteral Tonicity

Osmosis: Movement of solvent molecules across a semi-permeable membrane, from a high solvent concentration (low solute) to a low solvent concentration (high solute).
Open system: Adding solute lowers the vapor pressure on one side, causing solvent to move across the membrane, balancing vapor pressure and raising the solution side liquid level.
Osmotic pressure: The pressure needed to prevent solvent movement across a semi-permeable membrane. This pressure is the same on both sides of the membrane in equilibrium.
Colligative properties: Properties of solutions arising from solute particles disrupting solvent properties. These disruptions are directly influenced by the concentration of the solute, but not its identity

Colligative Properties

Lowering of Vapor Pressure: The addition of solute reduces the solvent's vapor pressure.
Boiling Point Elevation: Addition of solute increases the solvent's boiling point, due to the required increase in energy to overcome the reduced vapor pressure.
Freezing Point Depression: Addition of solute lowers the solvent's freezing point.

Osmolarity & Osmolality

Osmolarity: The number of osmotically active substances per liter of solution.
Osmolality: The number of osmotically active substances per kilogram of solvent.
1 Osmol: Represents the number of osmotically active substances associated with 1 mole.
Avogadro's number: 6.022 x 10²³ molecules/mole

Osmolarity/Osmolality values

1 Osmolar aqueous solution: Exerts an osmotic pressure of 22.4 atm at 0°C. Freezes at -1.86°C, and boils at 100.52°C

Tonicity

Tonicity: Measure of osmotic pressure gradient across a membrane, considering solutes that do not cross the membrane.
Isotonic: Solution that doesn't alter cell volume. The osmotic pressure is the same inside and outside of the cell.
Hypotonic: Lower osmotic pressure than the cell contents. Water moves into the cell, causing it to swell and potentially burst.
Hypertonic: Higher osmotic pressure than the cell contents: Water moves out of the cell, causing it to shrink.

Methods for Calculating Tonicity

Concentration Method: Assumes additive effects of all components in calculating the total osmolarity and adjusts accordingly to match a desired tonicity value for a formulation
Freezing Point Depression Method (FPD): Uses freezing point depression as a surrogate for osmotic pressure and additive effects.
Sodium Chloride Equivalent Method (SCE): Determines the amount of sodium chloride necessary to match the osmotic pressure of a given solution to ensure isotonicity.

Adjustment of Tonicity - SCE Method

Calculate: Total NaCl equivalent of all drug components.
Subtract: Calculated value from 0.9% standard value to determine the required NaCl adjustment.

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Description

Explore the concepts of parenteral tonicity and colligative properties, including osmosis, osmotic pressure, and the effects of solute on vapor pressure and boiling point. This quiz will test your understanding of how solute concentration influences solvent characteristics. Challenge your knowledge of these essential chemistry principles!