How much Methylene Blue is needed to make 120 mL of a 1 in 25,000 solution?

Question

BlackTom AI · Accepted Answer

A 1 in 25,000 solution means 1 part of solute per 25,000 parts of solution (commonly interpreted as 1 g solute per 25,000 mL solution when using g/mL units). So use a simple proportion to find the mass required for 120 mL.

1. Relevant knowledge points and concepts
- "1 in 25,000" = 1 unit mass of solute per 25,000 units volume (here 1 g per 25,000 mL is the working convention).
- Use direct proportion (or unit factor) and convert grams to milligrams (1 g = 1000 mg).

2. Step-by-step reasoning and calculations
- Set up the proportion: 1 g : 25,000 mL = x g : 120 mL.
- Solve for x (grams): x = (1 g × 120 mL) / 25,000 mL = 120 / 25,000 g.
- Compute the fraction: 120 / 25,000 = 0.0048 g.
- Convert grams to milligrams: 0.0048 g × 1000 mg/g = 4.8 mg.

3. Intermediate steps shown
- 120 ÷ 25,000 = 0.0048 (g)
- 0.0048 × 1000 = 4.8 mg

4. Why the correct answer is correct
- The arithmetic follows directly from the definition of "1 in 25,000" and correct unit conversion, yielding 4.8 mg of methylene blue needed to make 120 mL of that dilution.

5. Why the other options are incorrect
- a. 4.4 mg, c. 5.2 mg, d. 7.1 mg, e. 9.6 mg do not match the exact proportion and unit conversion above; they are either under- or overestimates compared with the correct calculation (120/25,000 g → 4.8 mg).

Conclusion: The correct amount is 4.8 mg, matching answer b.

How much Methylene Blue is needed to make 120 mL of a 1 in 25,000 solution?Single choice

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