STOCK SOLUTIONS, DILUTIONS AND ALLIGATION

Q: What is the concentration or strength of a solution?

A: The quantity of an active or additional ingredient to use to achieve the desired drug or ingredient concentration.

Q: List three different units in which concentration can be expressed.

A: mg/mL or g/L, %W/V ratio strength, Molar, or parts per million.

Q: What are stock solutions?

A: Strong or very concentrated solutions of active (e.g., drug) or inactive (e.g., colourants, flavouring agents) substances that are frequently purchased commercially or prepared for convenience of dispensing.

Q: What are stock solutions used for?

A: They are used to facilitate the preparation of solutions at lesser concentration.

Q: Define the process of dilution.

A: The process of adding additional solvent/diluent to a solution to decrease its concentration.

Q: What happens to the amount of solute and the total volume during dilution?

A: The amount of solute remains constant, but the total amount of solution increases, hence decreasing its final concentration.

Q: What is the fundamental formula used for dilution calculations?

A: Quantity1 x Strength1 = Quantity2 x Strength2 OR V1 x C1 = V2 x C2.

Q: What is a diluent and what must it be compatible with?

A: A diluent is a vehicle or solvent used to dilute, and it must be compatible with the vehicle of the original product.

Q: In pharmacy, what is the Minimum Weighable Quantity (MWQ)?

A: The Minimum Weighable Quantity is 100mg

Q: What is trituration?

A: Trituration is the dilution of potent medicinal substances with finely powdered lactose (diluent), usually 1:10 (w/w) mixtures

Q: What is the purpose of using trituration in pharmacy?

A: It is a means of obtaining accurately small quantities of potent drugs for compounding, especially when the required amount is less than the Minimum Weighable Quantity

Q: What is the Alligation method?

A: An arithmetical method of solving problems that involves the mixing of solutions or mixtures of solids with different percentage (%) strengths.

Q: What is Alligation Medial used to calculate?

A: It calculates the weighted average percentage strength of a mixture.

Q: What is Alligation Alternate used to find?

A: It is used to find the number of parts of two components with different strengths (high & low) that must be mixed to prepare a mixture of a desired strength (in between the high & low).