[aimz_186]

HEy guys,
having trouble with this....

2Al(OH)3 + 3H2SO4 goes to Al2SO3 + 6H20

If 15.0g of Al(OH)2 and 20.0g of H2SO4 are mixed together, the number of grams of Al(OH)3 left unreated at the end of the reaction is;

a)0
b)4.4g
c)10.6g
d)11.7g

So far i have only worked out the moles of Al(OH)3 is 0.1923
and the moles of H2SO4 is .20389

from there im stuck... thanks in advance for any help

[kkrizka]

Use stoichiometry. For every 2 moles of Aluminum Hydroxide, 3 moles of Sulfuric acid reacts. You can use dimensional analysis to find out the amount of Aluminum Hydroxide reacted:
.20389 mol H2SO4 x 2 mol Al(OH)3
                              -------------
                              3 mol H2SO4

Then just substract this amount from the initial amount of Aluminum Hydroxide and use molar mass to convert it back to grams.

[AWK]

Al2SO3  should be Al2(SO4)3
You can replace moles by masses of reactants. Since there is indicated which is a limiting reactant, you cen lay down the following equation
x/156 = 20/294 (note x is a mass of reacted Al(OH)3 )