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Analysis of a compound known to contain only Mg, P and O gives this analysis.21.8%Mg,...

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lak-86 | Student, Undergraduate | (Level 1) Salutatorian

Posted August 14, 2013 at 6:57 PM via web

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Analysis of a compound known to contain only Mg, P and O gives this analysis.
21.8%Mg, 27.7% P and 50.3% O. What is its empirical formula?
(A) MgPO2

(B) MgPO3
(C) Mg2P2O7    

(D) Mg3P2O8

1 Answer | Add Yours

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted August 14, 2013 at 7:11 PM (Answer #1)

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Molar mass in g/mol

Mg = 24

P = 31

O = 16

Let us say we have 100g of the compound. Then we have 21.8  g of Mg, 27.7g of P and 50.3g of O.

Amount of Mg moles `= 21.8/24 = 0.91`

Amount of P moles `= 27.7/31 = 0.894`

Amount of O moles `= 50.3/16 = 3.144`

Mole ratio

`Mg : P : O `

`= 0.91 : 0.89 : 3.144 `

`= 0.91/0.89 : 0.89/0.89 : 3.144/0.89 `

`= 1 : 1 : 3.5`

`= 2 : 2 : 7`

So the emperical formulae is `Mg_2P_2O_7` . The correct answer is C.

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