47.05%
We are given;
Mass of a solid hydrate = 2.682 grams
Mass of the solid anhydrous residue = 1.420 grams
We are required to determine the percent of water hydrate;
Mass of water = Mass of the solid hydrate - mass of the anhydrous residue
Therefore;
Mass of water = 2.682 g - 1.420 g
= 1.262 g
% water in the hydrate = (mass of water ÷ mass of the solid hydrate)×100%
Therefore;
% water in the hydrate = (1.262 g ÷ 2.682 g) × 100%
= 47.05%
Hence, the percent water in the hydrate is 47.05%