Magnesium hydroxide is 54.87% oxygen by mass. How many grams of oxygen are in 175g of the compound?

How many moles of oxygen is this?

simple. if you had 100% oxygen and 175g of (example i know mass,etc) then 175g would be oxygen. For your analysis only 54.87% of 175 therefore 96.0225g oxygen. HOw……….devide 175g(your mass) by 100(to get % for 1%) then multiply by your 54.87(your % purity).

1 mole of oxygen(O2) = 32g therefore

96g O2 = 3 moles oxygen.enjoy.

(96/32, nb not 16 as moles of oxygen is a diatomic molecule you did not say O^-. oxygen atom is 16, oxygen molecule is O2)

You better get an idea of what you are doing; this is pretty fundamental stuff. To get grams, remember that a percentage can be converted to a decimal; it is 0.5487. So any mass of Mg(OH)2 is multiplied by 0.5487 to get the grams of oxygen. To get the MOLES of oxygen, we divide the result of the grams part by 32. 32 is needed, since oxygen occurs as a dimer molecule O=O.