Homework Help: chem

Posted by ashley on Sunday, March 23, 2008 at 2:24pm.

mass of mg- .28
mass of o- .41

calculate the moles of mg and o

what is the simples whole number ratio of the moles of mg to the moles of o? round off to the nearest whole number ratio. use this mole ratio to write the empirical formula.

the molecular mass of magnesium oxide is found to be 40.3 g/mol. what isthe molecular formula?

chem - Damon, Sunday, March 23, 2008 at 4:46pm
O weighs 16 grams/mole
Mg weighs 24.3 g/mole

if it were MgO it would be 16+24.3 = 40.3 grams/mole so that is what it is

Now I suspect your real question was if you have .28 grams of Mg and .41 grams of O in a compound, what is the compound?
Mass Of Mg/ molecular mass = .28/24.3 = .0115
mass of O/molecular mass = .41/16 = .0256
so we have .0256 moles of O to .0115 moles of Mg
.0256/.0115 = 2.224
I suppose that could be Mg3O7 for a ratio of 2.3333etc
or perhaps Mg4O9 for a ratio of 2.25 (pretty close)
but I bet it is MgO2 for a ratio of 2 (the simple whole number they want is 2 :)

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