MgSO4*xH2O.... what is x?

Question

Epsom salts, a strong laxative used in veterinary medicine, is a hydrate, which means that a certain number of water molecules are included in the solid structure. The formula for Epsom salts can be written as MgSO4•xH2O, where x indicates the number of moles of water per mole of magnesium sulfate. When 5.061 g of this hydrate is heated to 250*C, all the water of hydration is lost, leaving 2.472 g of MgSO4. What is the value of x? [Hint: Find the moles of water lost & moles of compound MgSO4 remaining. The ratio of water to compound = coefficient x]

Answer 1

H2O MW = 18 g/mole

MgSO4 MW = 120.37 g/mole

weight hydrate = 5.061 g
weight anhdyrous = 2.472 g

difference = 5.061 g - 2.472 g = 2.589 g

all this is due to water

2.472 g is due to MgSO4

so moles of MgSO4 = 0.0205 moles

moles of water liberatered = 2.589g / 18g/mole = 0.144 moles

0.144 mole H2O/0.0205 moles MgSO4 = 7

so the hydrate is MgSO4 • 7 H2O

Answer 2

First of all crystals of MgSO4 hold 'x' number of moles of water within the crystal lattice. This is known as the 'Water of Crystalisation'.
Mass of water lost is 5.061 - 2.472 = 2.589 g
Moles of water = 2.589/18 = 0.143833333..
(NB 18 is the Mr of water).

Moles MgSO4 remaining
Mr (MgSO4)
Mg x 1 = 24 x 1 = 24
S x 1 = 32 x 1 = 32
O x 4 = 16 x 4 = 64
24 + 32 + 64 = 120 (Mr MgSO4)

Moles(MgSO4) = 2.472/120 = 0.0206
Compare the molar ratios

MgSO4 : H2O :: 0.0206 : 0.1438333333.
Divide the all the ratios by the smallest ratio

MgSO4 : H2O :: 0.0206/0/0206 : 0.1438333333/0.0206
MgSO4 : H2O :: 1 : 6.9822 (or approx. 7)
So there are 7 moles of water per 1 mole of MgSO4
MgSO4.7H2O the answer !!!!!!

Answer 3

The hint tells you exactly what to do.

Grams of water lost = 5.061-2.472= 2.589
Moles of water lost = 2.589g / 18.016g/mole = 0.1437 moles
Moles of MgSO4 remaining = 2.472 g / 120.386 g/mole = 0.02053 moles
0.1437 moles H2O : 0.02053 moles of MgSO4
ratio = 7 : 1
MgSO4.7H2O

Answer 4

Mgso4 H20