22. A pharmacy technician is preparing to compound a prescription that requires 120 mL of a 2% w/v solution of a drug. How many grams of the drug are needed?
Answer: B
2.4 grams of the drug are needed.
To prepare 120 mL of a 2% w/v solution, the technician needs to calculate the amount of drug required in grams. A 2% w/v solution means there are 2 grams of the drug in every 100 mL of solution. Therefore, for 120 mL, 2.4 grams of the drug are necessary.
A) 0.24
This option is incorrect because 0.24 grams would only be sufficient for a much smaller volume of solution. Specifically, at a 2% concentration, 0.24 grams would correspond to only about 12 mL of solution, which does not meet the 120 mL requirement.
B) 2.4
This option is correct as it accurately represents the amount of drug needed to prepare 120 mL of a 2% w/v solution. The calculation shows that 2% of 120 mL equals 2.4 grams, aligning perfectly with the requirement.
C) 12
This option is incorrect because 12 grams significantly exceeds the amount required for a 120 mL solution at a 2% concentration. In fact, 12 grams would yield a much higher concentration than 2%, indicating a misunderstanding of the percentage calculation.
D) 24
This option is also incorrect, as 24 grams is far too much for a 120 mL solution at 2% w/v. Such a quantity would result in an excessively concentrated solution, demonstrating a fundamental error in understanding the calculations necessary for compounding.
Conclusion
The correct answer is 2.4 grams, as it precisely meets the requirements for compounding a 120 mL solution at a 2% w/v concentration. Other options either underestimate or overestimate the required amount of the drug, indicating errors in the calculations related to weight/volume percentages.