Calculate the mass of hydrogen formed when 27 g of
aluminum reacts with excess hydrochloric acid according
to the balanced equation below.
2A1 + 6HCl → 2 AlCl3 + 3 H2

Mass of H₂ formed = 3 g

Explanation:

Given data:

Mass of Al react = 27 g

Mass of H₂ formed = ?

Solution:

Chemical equation:

2Al + 6HCl     →       2AlCl₃ + 3H₂

Number of moles of Al:

Number of moles = mass/ molar mass

Number of moles = 27 g/ 27 g/mol

Number of moles = 1 mol

Now we will compare the moles of Al with hydrogen.

                         Al            :         H₂

                         2             :           3

                         1              :          3/2×1 = 1.5    

Mass of H₂:

Mass = number of moles × molar mass

Mass = 1.5 mol × 2 g/mol

Mass = 3 g

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.