Wednesday
May 4, 2016

Homework Help: Chemistry

Posted by Britney on Sunday, March 18, 2007 at 8:28pm.

If 20.0 grams of Al is placed into a solution containing 115 grams of H2SO4, how many grams of hydrogen gas could be produced?

1. Write the balanced equation.
2Al + 3H2SO4 ==> Al2(SO4)3 + 3H2

2. Convert 20.0 g Al to mols.
Remember mols = g/atomic mass

3. Using the coefficients in the balanced equation, convert mols Al to mols H2 gas.

4. Convert mols H2 gas to grams.
grams = mols x molar mass.

Post your work if you need further assistance.

2Al + 3H2SO4 ==> Al2(SO4)3 + 3H2
20.0/27=.741mols
after that im stuck

1. Write the balanced equation.
2Al + 3H2SO4 ==> Al2(SO4)3 + 3H2
done

2. Convert 20.0 g Al to mols.
Remember mols = g/atomic mass
correct. 20.0/26.98 = 0.741 mols Al

3. Using the coefficients in the balanced equation, convert mols Al to mols H2 gas.
Now use the coefficients of the balanced equation to convert what you have (in this case mols Al) to mols of what you want (in this case mols H2).
mols H2 = 0.741 mols Al x (3 mol H2/2 mols Al) = 1.11 mols H2. Notice that the unit mols Al in the denominator cancel with mols Al in the numerator leaving mols H2 as the only unit and that is what you want. All conversions are done this way; i.e., use a factor that cancels the unit we don't want and leave the unit we want to keep.

4. Convert mols H2 gas to grams.
grams = mols x molar mass.
Can you finish?

mols H2 = 0.741 mols Al x (3 mol H2/2 mols Al) = 1.11 mols H2.
1.11 x 2 =2.22g

correct. I hope you understand how to make the conversions now. Once you get the hang of that these problems become easier and easier.