The amount of calcium present in milk can be determined through gravimetric analysis by adding oxalate to a sample and measuring the mass of calcium oxalate precipitated. What is the mass percent of calcium in milk if 0.429 g of calcium oxalate, CaC2O4, forms in a 125-g sample of milk when excess aqueous sodium oxalate is added?
Na2C2O4 (aq) + Ca2+ (aq) → CaC2O4 (s) + 2 Na+ (aq)

0.343%
1.10%
1.37%
0.202%
0.107%

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%

може ли да зареждате повече информация, моля