How can you determine the mass of liquid bromine needed to react completely with a given mass of magnesium

Question

Chemistry homework question

Answer 1

You must work with MOLES, not mass.

To determine the mass of Br2 needed to react with a given mass of Mg, first write the balanced equation:

Mg + Br₂ ==> MgBr₂ ... balanced equation

Next, convert the mass of Mg to moles of Mg by dividing the mass by the atomic mass of Mg (24.3 g/mol)

Next, use the mole ratio of the balanced equation to find moles of Br₂ needed. It will be the same as the moles of Mg used since the mol ratio is 1:1

Finally, convert moles of Br₂ to grams Br₂ by multiplying by the molar mass Br₂ (160 g/mol)

Example using 15 g of Mg:

15 g Mg x 1 mol Mg / 24.3 g Mg = 0.617 mols Mg

moles Br₂ needed = 0.617 mols Mg x 1 mol Br₂ / mol Mg = 0.617 moles Br₂ needed

mass Br₂ = 0.617 mols Br₂ x 160 g / mol = 98.8 g Br₂