Final answer:
At 40ᵒC, the mass of oxygen that will dissolve in 300g of water is 12mg.
Step-by-step explanation:
To find the mass of oxygen that will dissolve in 300g of water, we can use the solubility information given for oxygen in water. At 40°C, oxygen has a solubility of 4mg per 100g of water. This means that for every 100g of water, 4mg of oxygen will dissolve.
To find the mass that will dissolve in 300g of water, we can set up a proportion:
4mg / 100g = x / 300g
Cross-multiplying, we get 100g * x = 4mg * 300g. Solving for x,
x = (4mg * 300g) / 100g = 12mg