Question

you measure the mass of MgSO4 hydrate to be 10.04g. after heating the hydrate and allowing it to cool, you measure the mass of the MgSO4 anhydrate to be 4.89g. what is the theoretical yield of anhydrate?

Answer 1

Mass of hydratedMgSO₄ = 10.04 g (hydrated formula MgSO₄ .xH₂O if x mole water molecule is there)

Mass of anhydrate MgSO4 = 4.89 g

Mass of Water Molecule = (10.04-4.98)g

= 5.06 g

We know, No of Moles = weightt/molecular weight

so no of moles of water = 5.06/18 ( Molecular weight (M.W.) of water is 18g/mol)

= 0.28 mol

no of moles of MgSO₄ = (4.89/120)................(weight of anhydrous MgSO₄ = 4.89 g and molar mass of MgSO₄ = 120g/mol)

= 0.04 mol  

no of moles of water/no of moles of MgSO₄ = 0.28/0.04

= 7

So there is 7 water molecule present with 1 molecule of MgSO₄ in the hydrated form.

The formula of hydrated is (MgSO₄ .7H₂ O)

MgSO₄ .7H₂ O (hydrated) is converting to MgSO₄ (anhydrate)

Molar Mass : 246g/mol 120g/mol

1 mole of hydrated MgSO₄ is giving 1 mole of anhydrate MgSO₄

means 246 g of hydrated MgSO₄ will give 120g of anhydrate MgSO₄

so, 10.04 g of hydrated MgSO₄ will give (120*10.04/246) g of anhydrate MgSO₄

= 4.89 g of anhydrate MgSO₄

The theoretical yield of anhydrate is 4.89 g