Ontario Registered Pharmacy Technician (RphT) Practice Exam

A pharmacy has 20mL of a 1:2000 solution in stock. If the pharmacist asks the technician to dilute the solution to 500mL, how should the final strength of the solution be labeled?

1. 2%

2. 2.5%

3. 25%

4. 0.02%

The correct answer is: 0.02%

When diluting a solution, the resulting strength is typically labeled as a ratio or percentage. In this case, the solution is being diluted from a 12000 ratio to a 1:500 ratio. This means that for every 1 unit of the original solution, there will now be 1/4 unit in the final solution. Therefore, the final strength can be expressed as a fraction, 1/2000, or as a decimal, 0.0005. The decimal form as a percentage would be 0.05%, but this is not one of the choices. Option D, 0.02%, is the closest answer as it represents the diluted solution strength as a percentage of the original solution. The other options do not accurately represent the dilution process or the final strength of the solution.