Question

A measurement of 5 ppm concentration is equivalent to

• A. 5 g/mL
• B. 5 mg/mL
• C. 5 µg/L
• D. 5 mg/L

Hint:

Easy Conversion:
- ppm = mg/L
- ppb = µg/L
Just remember that 1 liter of water = 1 kg = 1,000,000 mg.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to convert the concentration unit "ppm" (parts per million) into a standard metric weight-per-volume unit used in water chemistry.
Key Formula or Approach:
\[ \text{1 ppm} = \text{1 part of solute per 1,000,000 parts of solution} \] Since 1 liter of water has a mass of approximately 1,000 grams or 1,000,000 milligrams: \[ \text{1 ppm} = \frac{\text{1 mg}}{\text{1,000,000 mg}} = \frac{\text{1 mg}}{\text{1 liter}} \] Therefore: \[ \text{1 ppm} = \text{1 mg/L} \]

Step 2: Detailed Explanation:

• ppm to mg/L: As derived above, for dilute aqueous solutions, ppm and mg/L are numerically identical because 1 liter of water weighs exactly $10^6$ milligrams.

• Analysis of options:
- 5 g/mL: This would be 5,000,000 ppm.
- 5 mg/mL: This would be 5,000 ppm.
- 5 µg/L: This is 0.005 ppm (also called 5 ppb - parts per billion).
- 5 mg/L: This is exactly 5 ppm.

• Application: In aquaculture, we measure dissolved oxygen, ammonia, and chemical dosages in ppm or mg/L. For example, a dissolved oxygen level of 5 ppm means there are 5 milligrams of oxygen in every 1 liter of pond water.

Step 3: Final Answer:
5 ppm is equivalent to 5 mg/L.