Neco 2018 Chemistry Question 2

A lake with a volume of \(2.0\times10^{6}\)\,L has a dissolved‑oxygen (DO) concentration of \(8\)\,mg\,L\(^{-1}\) at \(20\,°C\). At \(30\,°C\) the saturation concentration of oxygen is \(7.6\)\,mg\,L\(^{-1}\). (a) Calculate the percentage decrease in DO saturation when the temperature rises from \(20\,°C\) to \(30\,°C\). (b) Determine the additional amount of oxygen (in mg) that must be supplied per litre to maintain the original DO level of \(8\)\,mg\,L\(^{-1}\). (c) If each fish consumes \(0.5\)\,mg of O\(_2\) per hour, estimate the maximum number of fish that can be supported in the lake after the temperature rise, assuming the extra oxygen calculated in part (b) is supplied continuously for 24 h.