Chemistry solve for x

Chemistry
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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 · x H2O, where x indicates the number of moles of H2O per mole of MgSO4. When 5.469 g of this hydrate is heated to 250°C, all the water of hydration is lost, leaving 2.671 g of MgSO4

WHAT IS THE VALUE OF X? IN THE CORRECT NUMBER OF SIGNIFICANT DIGITS

Jul 24th, 2015

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DATA:

mass of Epsom salt sample before heating =M1= 5.469g

Mass of Epsom salt sample after heating = M2= 2.671g

Moles of water of hydration=?

SOLUTION:

Mass of water in the washing soda sample= M1-M2

  = 5.469-2.671

Mass of water in the washing soda sample= 2.798g

Moles of water= mass of water in washing soda sample/ molecular mass of water

  = 2.798/18

Moles of water = 0.1554mol

Moles of MgSO4 after heating = M2/molecular mass of MgSO4

  = 2.671/120.32

Moles of MgSO4 after heating = 0.0221mol

Since the number of moles of each is not a whole number, we need to find the whole number ratio by dividing each by the smaller of the two:

Moles of MgSO4 = 0.0221/0.0221

Moles of MgSO4 = 1.00

Moles of water = 0.1554/0.0221

Moles of water= 7.0316

Since the ratio of moles of hydrated washing soda to water of hydration is 1 : 7, the formula would read MgSO4 ∙7H2O, and the value of "x" is 7.


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Jul 24th, 2015

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