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Preparing for the Pharmacy Technician Certification Board (PTCB) exam requires practicing a variety of questions, including those on dilution calculations. Understanding how to perform these calculations accurately is essential for pharmacy technicians to ensure proper medication preparation and safety. This article provides practice questions on dilution calculations along with detailed answers to help you succeed on the exam.
Understanding Dilution Calculations
Dilution involves reducing the concentration of a solute in a solution. The basic formula used in dilution calculations is:
C1 × V1 = C2 × V2
Where:
- C1 = initial concentration
- V1 = initial volume
- C2 = final concentration
- V2 = final volume
Knowing how to manipulate this formula allows you to find any missing value in a dilution problem.
Practice Questions with Answers
Below are sample questions to test your understanding of dilution calculations. Answers are provided at the end.
Question 1
A pharmacist needs to prepare 500 mL of a 10% solution from a stock solution that is 50%. How much of the stock solution is required?
Question 2
You have 200 mL of a 20% solution. How much water should be added to dilute it to a 10% solution?
Question 3
What volume of a 25% solution is needed to prepare 1 liter of a 5% solution?
Question 4
If 30 mL of a 15% solution is diluted to a final volume of 150 mL, what is the concentration of the final solution?
Answers and Explanations
Question 1: V1 = (C2 × V2) / C1 = (50% × 500 mL) / 10% = (50 × 500) / 10 = 25,000 / 10 = 2,500 mL. Since the stock solution is only 50%, this calculation shows the amount needed exceeds the stock concentration, indicating a need for a different approach or solution. Typically, this question demonstrates the importance of matching concentrations and volumes properly.
Question 2: Using C1V1 = C2V2, where V2 = 200 mL, C1 = 20%, C2 = 10%. V1 = (C2 × V2) / C1 = (10% × 200 mL) / 20% = (10 × 200) / 20 = 2,000 / 20 = 100 mL. Water to add = V2 – V1 = 200 mL – 100 mL = 100 mL.
Question 3: V1 = (C2 × V2) / C1 = (5% × 1000 mL) / 25% = (5 × 1000) / 25 = 5,000 / 25 = 200 mL.
Question 4: Using V1C1 = V2C2, V1 = (V2 × C2) / C1 = (150 mL × 15%) / 15% = (150 × 15) / 15 = 150 mL. Since 30 mL of a 15% solution was diluted to 150 mL, the concentration is (30 × 15%) / 150 mL = (30 × 15) / 150 = 450 / 150 = 3%. The final concentration is 3%.
Summary
Practicing dilution calculations is vital for pharmacy technicians. Remember the formula C1V1 = C2V2, and carefully analyze each problem. With consistent practice, you’ll improve your accuracy and confidence for the PTCB exam and real-world pharmacy tasks.