What tool do I need to use to find the molar mass?

I never thought of it as a tool, but I think you refer to Atomic Weight. The total atomic weight of the atoms in a molecule is its Mass in Moles.

Take a really simple example H2O. The atomic weight of Oxygen is 16, Hydrogen is 1, and so added, 1 + 1 + 16 = 18; the mass of 1 mole of water is 18g. Same for Benzene, C6H6; atomic weight of carbon is 12, so 6 x 12 = 72, add 6 x 1, or 6, and 72 + 6 = 78

Explanation: The sum of the atomic weights of the atoms in a molecule will give you the Molecular Weight, I.e. the Mass of 1 Mole of thst molecule.

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).

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%