Question

Q.-- A 1.0000 g sample of zinc metal is added to a solution containing 1.2500 g of an unknown compound of bismuth and chlorine. The reaction results in the formation of zinc chloride and metallic bismuth. When the reaction is complete, unreacted zinc remains, and this unreacted zinc is consumed by reaction with HCl. After washing and drying, the mass of bismuth metal recovered is 0.6763g

-- Calculate the experimental % of bismuth in the original unknown compound

-- If 2.300g of the unknown bismuth chloride had been used, how many grams of chlorine would you expect it to contain?

-- Determine the empirical formula of the original unknown compound

Answer 1

Answer - We are given, mass of Zn = 1.0000 g

Mass of unknown compound of bismuth and chlorine = 1.2500 g

Mass of bismuth metal recovered = 0.6763 g

The experimental % of bismuth in the original unknown compound –

We know formula for the percent mass as follow –

% of bismuth = mass of bismuth / total mass of unknown compound X 100 %

                      = 0.6763 g / 1.2500 g X 100 %

                     = 54.10 %

In the unknown compound of bismuth and chlorine there are 0.6763 g of Bi and there is 54.10 % of Bi in the bismuth and chlorine compound.

% of Cl = 100 – 54.10

             = 45.90 %

Mass of Cl = % of Cl X mass of unknown compound / 100 %

                  = 45.91 % X 2.300 g / 100 %

              = 1.056 g

Now we know the mass of Bi and Cl, so need to convert first moles of both

Moles of Bi = 0.6763 g / 208.98 g.mol^-1

                    = 0.003236 moles

Mass of Cl the original unknown compound = 1.2500 g – 0.6763 g

                                                                 = 0.5737 g

Moles of Cl = 0.5737 g / 35.453 g.mol^-1

                   = 0.01618 moles

Lowest moles is for Bi, so need to divided each moles by the moles of Bi

Bi = 0.003236 /0.003236 = 1

Cl = 0.01618 / 0.003236 = 5

So empirical formula is BiCl₅