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### Topic: Binary mixture - percent composition  (Read 5101 times)

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#### tiny101

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##### Binary mixture - percent composition
« on: October 01, 2008, 07:13:25 PM »
Hello, I've hit a road block with this question and I'm hoping someone can point me in the right direction.

The problem states that a 5.30-g sample containing only Mn2(SO4)3(s) and Al2(SO4)3(s) is dissolved in aqueous solution. The metal ions are precipitated as hydroxides, which are pyrolyzed in air to produce 1.85 g of a mixture of Mn2O3(s) and Al2O3(s). What was the percent Mn in the original sample?

I've designated x = mass of Mn2O3 and with that, I found that the moles of Mn would be = 2x/157.87

What is the next step? Or, am I completely mistaken?

#### Borek

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##### Re: Binary mixture - percent composition
« Reply #1 on: October 02, 2008, 03:01:06 AM »
Assume x moles of manganese sulfate and y moles of aluminum sulfate. Write equations for mass of sulfates and mass of oxides (hint: use molar masses and stoichiometry). Two equations, two unknowns, simple algebra.
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#### tiny101

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##### Re: Binary mixture - percent composition
« Reply #2 on: October 02, 2008, 08:37:45 PM »
How would I write the equation for the mass of oxides? Should I write up the chemical equations (as in how they react with one another) to figure out the moles of the oxides, then write the equation?

Thanks again.

#### Borek

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##### Re: Binary mixture - percent composition
« Reply #3 on: October 03, 2008, 04:18:19 AM »
Assume there are x moles of Mn.

What will be mass of the Mn2(SO4)3?

What will be mass of the Mn2O3?

These are very basic moles/mass conversions.

Now think - does the number of moles of Mx (x) change during the reactions, or not?
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