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A 311.86 gram sample of a substance is found to consist of 35.23% manganese,35.89%...

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lvart15 | eNotes Newbie

Posted February 7, 2013 at 1:28 AM via web

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A 311.86 gram sample of a substance is found to consist of 35.23% manganese,35.89% oxygen, and 28.88% water.  What is the formula and name of this substance?

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jerichorayel | College Teacher | (Level 1) Senior Educator

Posted February 7, 2013 at 2:40 AM (Answer #1)

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To solve for the formula of the compound, first we have to know the mass of the unknown substance. We let substance x (unknown) be 311.86 grams. 

Out of 311.86 grams of x:

`311.86 * (35.23)/(100) = 109.868 grams Mn`

`311.86 * (35.89)/(100) = 111.927 grams O`

`311.86 * (28.88)/(100) = 90.065 grams H2O`

From the mass of the components, we can get their mole equivalent using the molar mass.

`109.868 grams Mn * (1 mol e Mn)/(54.938 grams Mn)`

= 1.9999 moles = 2

`111.927 grams O * (1 mol e O)/(15.999 grams O)`

= 6.9955 moles O = 7

`90.065 grams H2O * (1 mol e H2O)/(18.015 grams H2O)`

= 4.9995 moles H2O = 5

 

Finally, we can use the whole number mole equivalent and write the molecular formula of the compound.

`Mn2O7*5(H2O)`

This compound is known as Manganese heptoxide pentahydrate. The IUPAC name for this compound is Manganese(VII) oxide pentahydrate.



 

 

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