Question

We are doing a lab on Grignard Reactions, i'm just looking to verify the system by which to find this information: Add about 2 mmol Mg powder, recording the mass to the nearest milligram. In this experiment, magnesium will be the limiting reactant because a 5% excess of bromobenzene will be used. Using your mass of Mg, determine the mass of bromobenzene to be used, being sure to calculate a 5% molar excess.

Answer 1

Solution :-

Mg used = 2 mmol

mole ratio of the Mg to bromobenzene is 1 : 1

we have to use 5 % moles of the bromobenzene.

so the amount of the bromobenzene needed = 2 mmol + (2 mmol * 5% /100%) = 2.1 mmol

2.1 mmol * 1 mol / 1000 mmol = 0.0021 mol bromobenzene

now lets convert the moles of bromobenzene to its mass

mass of bromobenzene = moles * molar mass

                                     = 0.0021 mol * 157.01 g per mol

                                    = 0.33 g

so the mass of the bromobenzene needed 0.33 g or we can write it as 330 mg