Chapter 19, Problem 7RAT

Fish don't live very long in water that has just been boiled and brought back to room temperature. Suggest why.

(a) There is now a higher concentration of dissolved ${\text{CO}}_{\text{2}}$ in the water.

(b) The nutrients in the water have been destroyed.

(c) Since some of the water was evaporated while boiling, the salts in the water are now more concentrated. This has a negative effect on the fish.

(d) The boiling process removes the air that was dissolved in the water. Upon cooling, the water is void of its usual air content, hence, the fish drown.

To determine

The reason why fish don’t live very long in water that has been boiled and brought back to room temperature.

Answer to Problem 7RAT

The best answer is option (d) as boiling removes the air dissolved in the water and on cooling the water will not have the usual air content, therefore fish can’t breathe properly and is drown.

Explanation of Solution

Fishes take up the oxygen dissolved in the water and it requires large volume of water to pass through their adsorption surfaces to get enough oxygen into their bodies.

Solubility of the gases in liquids decreases with increase in temperature. As on increasing the temperature, the solvent molecules will acquire more kinetic energy and which makes the solute molecules difficult to remain in solution as they are ejected by high-energy solvent molecules.

Fish don’t live very long in water which has been boiled and brought back to room temperature because the solubility of dissolved oxygen decreases on boiling and after cooling, the oxygen content would become less in water which makes difficult for the fish to breathe. So the fish don’t live for too long.

Conclusion:

Therefore the best option is (d).