4.10 g of hydrated magnesium sulphate crystals MgSO4．xH2O gave 2.00 g of anhydrous salt on careful heating. Calculate the formula of the hydrated salt.
Find x..
(molar mass : Mg:24 ; S:32 ; O:16 ; H:1)
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2006-11-17 4:47 am
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2006-11-17 5:10 am
✔ 最佳答案
Molar mass of MgSO4 = 24 + 32 + 4x16 = 120 gMolar mass of H2O = 2x1 + 16 = 18 g
In 4.10 g of MgSO4•xH2O :
Mass of MgSO4 = 2.00 g
Mass of H2O = 4.10 - 2.00 = 2.10 g
Since no. of moles of a substance = (mass / molar mass)
Mole ratio MgSO4 : H2O
= (2.00/120) : (2.10/18)
= 0.0167 : 0.117
≈ 1 : 7
But in MgSO4•xH2O, mole ratio MgSO4 : xH2O = 1 : x
Hence, x = 7
2006-11-17 5:05 am
MgSO4．xH2O ----> MgSO4 + xH2O
mole ratio of MgSO4．xH2O to MgSO4 = 1:1
=> mole of MgSO4．xH2O = mole of MgSO4
4.1/( 24+32+16*4+18x ) = 2/(24+32+16*4)
246 = 120+18x
x=7
mole ratio of MgSO4．xH2O to MgSO4 = 1:1
=> mole of MgSO4．xH2O = mole of MgSO4
4.1/( 24+32+16*4+18x ) = 2/(24+32+16*4)
246 = 120+18x
x=7
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