NAPLEX Dilution Board Practice Question, Video Explanation

Gearing up for your NAPLEX exam? Studying to be a pharmacist can fill your brain with countless calculations, side-effects, and complicated medication names, to stay sharp for your exam, you’ll need to do practice questions. We’ve pulled one question on dilution that has proven particularly complicated for our users from the NAPLEX Question Bank. Can you answer it correctly?

How many ml of a 1:4 solution of drug X is required to produce 4 liters of a 1: 20 w/v solution? (Answer in numeric value only rounded to the nearest whole number.)

We called on our friends at MedCram to work with Dr. Roger Seheult to explain this question on dilution.

Question: How many ml of a 1:4 solution of drug X is required to produce 4 liters of a 1: 20 w/v solution? (Answer in numeric value only rounded to the nearest whole number.)

Answer: 800 ml
Explanation: Use the formula for dilution: Q1 x C1 = Q2 x C2 Convert the ratios into a % strength: 1/4 = 25% (C1) 1/20 = 5% (C2) Quantity 1 (initial quantity or volume) = x units Concentration 1 (Initial concentration in percentage of stock solution) = 25% Quantity 2 (final quantity or volume) = 4000 units Concentration 2 (Final concentration, expressed as a percentage) = 5% 25X = 5 x 4L 25X = 5 x 4000ml X = 20000/25 X = 800 ml This equation uses volume %.

Reference: Remington, J. P., & Beringer, P. (2006). Remington: The science and practice of pharmacy. Philadelphia, PA: Lippincott Williams & Wilkins.

Did you get it right before looking at the answer? Whether this is second nature to you, or you found it particularly confusing, you’ll need a wider net of practice to put your best foot forward for the NAPLEX. The BoardVitals NAPLEX question bank covers more than 1400 review questions targeted to the exam. The bank was recently updated for the new NACP Competency Statements and the NAPLEX content blueprint.

The NAPLEX exam is administered over the course of 6 hours and consists of 250 multiple choice items. This exam has notoriously difficult and complicated calculations. Based on interviews of people who have taken the NAPLEX, calculations make up approximately 30% of the exam.

The BoardVitals question bank is built to satisfy both areas outlined in the NABP NAPLEX Competency Statements

  • Area 1: Ensuring Safe and Effective Pharmacotherapy and Health Outcomes (67% of exam)
  • Area 2: Safe and Accurate Preparation, Compounding, Dispensing, and Administration of Medications and Provision of Health Care Products (33% of exam).

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