Order Entry and Processing is 22.5% of the scored PTCE (the PTCB exam). Answer 10 exam style questions on concentrations and dilutions and see exactly which concepts would cost you points on test day.
Start the 10 questions →How many grams of dextrose are contained in 500 mL of D5W (dextrose 5% w/v in water)?
These questions cover percent strength w/v: grams in a solution, percent strength w/v: sodium chloride, percent strength w/v: finding the percent, percent strength w/w: cream and ratio strength: mg in a volume. Each one shows the correct answer and why every other option is wrong, so a miss tells you exactly what to review before the PTCE.
Prefer to read first? Every question from the practice set above, with the correct answer and why each wrong option is wrong.
Answer: D. % w/v = grams per 100 mL. 5% = 5 g/100 mL. 500 mL x 5 g / 100 mL = 25 g.
Why not A: 2.5 g is a decimal-place error. 5% w/v is 5 g per 100 mL, so 500 mL holds 5 x 5 = 25 g.
Why not B: 250 g is the amount in 500 mL of a 50% solution (D50W), not 5%.
Why not C: 5 g is the amount in only 100 mL. The bag contains 500 mL.
Exam tactic: w/v percent = grams per 100 mL. Scale by volume / 100.
Answer: C. 0.9% w/v = 0.9 g per 100 mL. 1,000 mL x 0.9 g / 100 mL = 9 g.
Why not A: 0.9 g is the amount in 100 mL only. A 1,000 mL bag contains 10 times as much.
Why not B: 90 g treats 0.9% as 9 g per 100 mL, a decimal-place error.
Why not D: 4.5 g is the amount in 500 mL, half the bag.
Exam tactic: Know that 0.9% NaCl means 0.9 g/100 mL, or 9 g per liter.
Answer: B. % w/v = g / mL x 100 = 15 / 300 x 100 = 5%. Check: 5 g per 100 mL x 3 = 15 g in 300 mL.
Why not A: 20% inverts the fraction (300 / 15). Percent = grams of drug / mL of solution x 100.
Why not C: 0.05 is the fraction 15 / 300. It must be multiplied by 100 to become a percent.
Why not D: 0.5% is a decimal-place error. 15 g / 300 mL = 5 g per 100 mL = 5%.
Exam tactic: Percent = part / whole x 100, with grams over mL for w/v.
Answer: A. % w/w = grams of drug per 100 g of product. 1% = 1 g/100 g. 30 g x 1 / 100 = 0.3 g (300 mg).
Why not B: 3 g would be a 10% cream. 1% of 30 g is 0.3 g.
Why not C: 0.03 g is a decimal-place error, the amount in a 0.1% cream.
Why not D: 1 g reads 1% as 1 g per tube. 1% w/w means 1 g per 100 g.
Exam tactic: w/w percent = grams per 100 grams.
Answer: C. 1:1,000 = 1 g/1,000 mL = 1,000 mg/1,000 mL = 1 mg/mL. 0.3 mL x 1 mg/mL = 0.3 mg.
Why not A: 3 mg is a decimal-place error. 1:1,000 equals 1 mg/mL, so 0.3 mL holds 0.3 mg.
Why not B: 0.03 mg corresponds to a 1:10,000 solution (0.1 mg/mL), not 1:1,000.
Why not D: 30 mg misreads 1:1,000 as 100 mg/mL.
Exam tactic: 1:1,000 = 1 mg/mL. 1:10,000 = 0.1 mg/mL.
Answer: B. 1:1,000 = 1 / 1,000 = 0.001. 0.001 x 100 = 0.1%. Check: 0.1% = 0.1 g/100 mL = 1 g/1,000 mL.
Why not A: 1% equals 1:100, ten times stronger than 1:1,000.
Why not C: 0.01% equals 1:10,000, ten times weaker than 1:1,000.
Why not D: 10% equals 1:10. The ratio must be divided out (1 / 1,000) and then multiplied by 100.
Exam tactic: Ratio to percent: divide 1 by the second number, then x 100.
Answer: A. 0.02% = 0.02 g/100 mL. Set 0.02 / 100 = 1 / x, so x = 100 / 0.02 = 5,000. Ratio = 1:5,000.
Why not B: 1:500 equals 0.2%, ten times stronger than 0.02%.
Why not C: 1:50,000 equals 0.002%, ten times weaker than 0.02%.
Why not D: 1:2,000 equals 0.05%. Dividing 100 by 0.02 gives 5,000, not 2,000.
Exam tactic: Percent to ratio: 1:(100 / percent).
Answer: D. C1V1 = C2V2: 70% x V1 = 30% x 350 mL. V1 = 10,500 / 70 = 150 mL of 70% alcohol, plus 200 mL of water. Check: 150 x 0.70 = 105 mL alcohol in 350 mL = 30%.
Why not A: 816.7 mL puts the strengths in the wrong places (70 x 350 / 30). The stock is stronger, so less than 350 mL is needed.
Why not B: 105 mL is 30% of 350 mL, the amount of pure alcohol, not the volume of 70% stock.
Why not C: 200 mL is the volume of water to add, not the volume of 70% stock.
Exam tactic: Stronger stock always needs a smaller volume than the final volume.
Answer: C. C2 = C1V1 / V2 = 15% x 200 mL / (200 + 100) mL = 3,000 / 300 = 10%.
Why not A: 7.5% treats the final volume as 400 mL. 200 mL + 100 mL = 300 mL.
Why not B: 5% uses the 100 mL of water as V1 instead of the 200 mL of stock.
Why not D: 22.5% inverts the volumes (15 x 300 / 200). Adding water can only lower the strength.
Exam tactic: Final volume = stock + diluent. Diluting always lowers the percent.
Answer: B. C1V1 = C2V2: 25% x 10 mL = 2.5% x V2, so V2 = 250 / 2.5 = 100 mL. Diluent = 100 mL - 10 mL = 90 mL.
Why not A: 100 mL is the final volume. 10 mL of that is the original solution, so only 90 mL is added.
Why not C: 1 mL inverts the formula (10 x 2.5 / 25). Diluting to a weaker strength needs a larger volume.
Why not D: 9 mL is a decimal-place error. A tenfold dilution of 10 mL needs a 100 mL final volume.
Exam tactic: Find the final volume first, then subtract the starting volume.
The free 20 question diagnostic covers all 4 areas of the PTCE outline and shows the 3 fixes worth the most points.
Take the free diagnosticSee all 31 PTCB practice topics →