A chemist weighs a steel cylinder of compressed oxygen, O2, and finds that it has a mass of 1027.8 g. After some of the
oxygen is used in an experiment, the cylinder has a mass of
1023.2 g. How many moles of oxygen gas are used in the
experiment?
When answering this question include the following:
.
Explain how you found the mass of oxygen gas.
Explain how to find the molar mass of the compound.
Explain how many significant figures your answer needs to have.
The numerical answer
.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2