Answer:
0.723 moles (5 s.f.)
Explanation:
Whenever there is a chemical equation, ensure that it is balanced. This is because a balanced chemical equation tells us the mole ratio (not the ratio of their masses), which means the relationship of the number of moles of reactants or products with one another.
The chemical equation given has already been balanced. Looking at the coefficients of HBr and Ba(OH)₂, the mole ratio of HBr to Ba(OH)₂ is 2: 1.
• 1 mole of Ba(OH)₂ is needed to react with 2 mole of HBr
Find the number of moles of HBr present:
Number of moles= mass ÷mr
Amount of HBr
= 117 ÷(1 +79.9)
= 1.4462 moles (5 s.f.)
Since the amount of Ba(OH)₂ required is half the amount of HBr present,
amount of Ba(OH)₂ required
= 1.4462 ÷2
= 0.723 moles (3 s.f.)
Notes:
• mr
= relative molecular mass
= sum of relative atomic masses (which can be found in the periodic table) in a molecule
