Epsom Salt, MgSO_4 middot xH_2 O, is a water soluble MgSO_4 hydrate. If 9.86 g o
ID: 537224 • Letter: E
Question
Epsom Salt, MgSO_4 middot xH_2 O, is a water soluble MgSO_4 hydrate. If 9.86 g of Epsom Salt dissolved in 50 ml of water reacts with excess BaCl_2 (aq) 9.30 g of the insoluble BaSO_4 (s) is obtained after drying. Assume a quantitative yield and determine the formula of the Epsom Salt. MgSO_4 middot xH_2 O ------------------- > ^dissolve in 50 mL water MgSO_4 (aq) (The water of hydration becomes part of the water solvent.) MgSO_4 (aq) + BaCl_2 (aq) -------- > MgCl_2 (aq) + BaSO_4 (s) Determine the formula of the MgSO_4 hydrate. From the DATA (not the formula) calculate the % by mass of H_2 O in the hydrate.Explanation / Answer
moles BaSO4 formed = 9.3 g/233.38 g/mol
= 0.04 mol
mass of MgSO4 present = 0.04 mol x 120.366 g/mol
= 4.81464 g
mass of water in epsom salt = 9.86 - 4.81464
= 5.04536 g
moles water = 5.04536/18 = 0.2803 mol
ratio moles (water/MgSO4) = 7
Water of hydration = 7
Formula of Epsom salt = MgSO4.7H2O
% mass og H2O in the hydrate = 5.04536 g x 100/9.86 g
= 51.17%
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