Chemistry stoichiometry

Question

if you start with 75 grams of Aluminum, how many grams of HBr would you need?

2Al+6Br->2AlBr3+3H2

Answer 1

We need to first find the molar mass of Aluminum, which is 26.98 g.

Now that we have that information, we have to convert Aluminum into moles. So, we do 75 g/26.98 g/mol=2.78 moles.

Let's do some stoichiometry now. According to the reaction, two moles of Aluminum react with 6 moles of HBr.

So, we must do 2.78 moles of Aluminum*6 moles of HBr/2 moles of Aluminum=8.34 moles.

Now, we must find the molar mass of HBr, which is 80.91 g. 2.78 moles*80.91 g/mol is 224.93 g.