ATI TEAS (Test of Essential Academic Skills) Version 7MathematicsMedium
A medical assistant needs to prepare a 0.9% saline solution. If they have 45 grams of sodium chloride, how many milliliters of sterile water are needed to achieve the correct concentration?
- A500 mL
- B40.5 mL
- C5000 mL
- D450 mL
Show answer & explanationAnswer & explanation
Correct answer: C. 5000 mL
A 0.9% (w/v) saline solution means 0.9 grams of sodium chloride per 100 mL of solution. To find the total volume for 45 grams, set up a proportion: 0.9g/100mL = 45g/x mL. Solving for x gives 5000 mL.
Why the other options are wrong
- A. This would be a 9% solution (45g/500mL).
- B. This calculation incorrectly multiplies 45 by 0.9.
- D. This would be a 10% solution (45g/450mL).
Percentage Concentration (w/v)
Weight by volume percentage (w/v) expresses the number of grams of solute in 100 milliliters of solution.
- Units are typically grams per 100 mL.
- Used for solid solutes dissolved in liquid solvents.
- A common way to express solution strength in healthcare.
Memory trick: Grams on top, mL on the bottom, times 100, that's the percent solution's song!