11. 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 must calculate the amount of drug required, which is 2.4 grams.
A) 0.24
This option is incorrect because 0.24 grams would represent a much lower concentration than required for a 2% w/v solution. To calculate the amount needed, one must consider that 2% w/v means 2 grams of drug per 100 mL of solution; therefore, 120 mL would need more than 0.24 grams.
B) 2.4
This option is correct as it accurately represents the amount of drug required for the preparation of 120 mL of a 2% w/v solution. The calculation involves determining 2 grams of drug per 100 mL, so for 120 mL, the calculation is (120 mL * 2 g) / 100 mL = 2.4 grams.
C) 12
This option is incorrect because 12 grams would be far too much drug for a 120 mL solution at a 2% concentration. The calculation shows that only 2.4 grams are needed, making 12 grams excessive and not fitting the prescription requirements.
D) 24
This option is also incorrect, as 24 grams exceeds the requirement for a 2% w/v solution in 120 mL. Using the same calculation approach, only 2.4 grams is necessary, demonstrating that 24 grams would result in a concentration that is significantly higher than intended.
Conclusion
The correct amount of drug needed is 2.4 grams, as this aligns with the requirements for a 2% w/v solution in 120 mL. Other options, such as 0.24 grams, 12 grams, and 24 grams, fail to meet the prescribed concentration, confirming that they are not suitable choices for compounding this prescription.