Select all the correct locations on the image. the heating curve shows temperature vs. energy gain. which parts of the curve represent a gain in potential energy?

The part of the graph which is marked by 2nd and 4th boxes are the regions where the substance gains potential energy.

Potential energy in the matter is stored in form of chemical energy in the chemical bonds. At this point, the temperature of the substance doesn't rise. But when the temperature rises, actually the kinetic energy of the substance rise, because of the molecular vibration.

In the graph, the line marks a distinct pattern where the temperature rises at certain places, and in certain places, it's still, even if the energy is supplied. So here in the parts of graph where it shows a horizontal curve, the potential energy of the matter rise.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%