Mercury and bromine will react with each other to produce mercuric bromide. What mass of mercuric bromide can be produced from the reaction of 5.00 mL mercury (density 13.5 g/mL) and 5.00 mL bromine (density 3.2 g/mL)? What volume in mL of excess reactant remains?

Answer 1

This is a limiting reagent (LR) problem and I know this because amounts are given for BOTH reactants. Therefore, one will be used completely (the LR) and the other will have some un-reacted.
Hg + Br2 ==> HgBr2

Use density to convert mL Hg to grams.
Do the same for mL Br2 to grams.

Convert g Hg to mols. mol = grams/atomic mass
Convert g Brw to mols. mol = g/molar mass.

Using the coefficients in the balanced equation convert mols Hg to mol HgBr.
Do the same for mols Br2 to mols HgBr2.
It is likely that these two values will not agree; the correrct answer in LR problems is ALWAYS the smaller value and the reagent producing that number is the LR..

Using the smaller value, convert to grams.
grams = mols x molar mass