Question

one litre of sea water weighs 1050 grams and contains 6x10^-3g of dissolved oxygen gas. Calculate the concentration of oxygen in ppm

Answer 1

5.714

Answer 2

The concentration in parts per million (ppm) is defined as the mass of solute per mass of solution multiplied by $10^6$.

$$\text{Concentration (ppm)} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 10^6$$

Given:

• Mass of dissolved oxygen (solute) = $6 \times 10^{-3} \text{ g}$
• Mass of sea water (solution) = $1050 \text{ g}$

Substitute the given values into the formula:

$$\text{Concentration (ppm)} = \frac{6 \times 10^{-3} \text{ g}}{1050 \text{ g}} \times 10^6$$ $$\text{Concentration (ppm)} = \frac{6}{1050} \times 10^{-3} \times 10^6$$ $$\text{Concentration (ppm)} = \frac{6}{1050} \times 10^3$$ $$\text{Concentration (ppm)} = \frac{6000}{1050}$$ $$\text{Concentration (ppm)} = \frac{600}{105}$$ $$\text{Concentration (ppm)} \approx 5.714$$

Rounding to two significant figures, the concentration is 5.7 ppm.

Explanation of the solution: The concentration in ppm is calculated using the formula: (mass of solute / mass of solution) × 10⁶. Given mass of oxygen (solute) as $6 \times 10^{-3}$ g and mass of sea water (solution) as 1050 g, substitute these values into the formula: $(6 \times 10^{-3} \text{ g} / 1050 \text{ g}) \times 10^6 = 5.714 \text{ ppm}$.