4. Anh measured the temperature of a pond near his house. Before he left for school, the water in the pond was 18°C. When he came home from school, the temperature of the pond was higher than it
was in the morning. What happened to the water molecules while he was at school?

The water molecules must have gained more thermal energy while Anh was away from the house.

An increase in the temperature of a body means that the body has gained more energy in the form of heat, also known as thermal energy.

The thermal energy represents the characteristic of a body responsible for its temperature.

An increase in the temperature of the water molecules increases their kinetic energy and, thus, makes the water molecules move around faster than before.

More on thermal energy can be found here: link

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.