Chemistry help... please help me on this one..

Question

i know how to do many problems like this but this one confuses me..

4. How many grams of aluminum would react completely with 17.50 grams of copper (II) chloride according to the following equation? Al(s) CuCl2(aq) ---> AlCl3(aq) Cu(s)

Answer 1

The first step is to balance the equation:

2Al + 3CuCl2 ---> 2AlCl3 + 3Cu

The next step is to find the number of moles of copper (II) chloride that reacts in the reaction. The molar mass of copper (II) chloride is the molar mass of copper plus two times the molar mass of chlorine:

63.546 g/mol + 2 * 35.453 g/mol = 134.452 g/mol

Calculate the number of moles in 17.5g CuCl2:

17.5g / 134.452g/mol = .130158 mol

2/3 times the number of moles of CuCl2 is equal to the moles of Al because CuCl2 has a coefficient of 3 and Al has a coefficient of 2.

2/3* .130158 mol =.086772 mol

The final step is to convert the number of moles to mass using the molar mass of aluminum, 26.982:

.086772 mol * 26.982 g/mol = 2.341282g

There are 4 significant figures in 17.50, so we must reduce the number calculated above to this number of figures. The final answer is 2.431g.

Answer 2

That equation needs to be balanced, too.