The concentration of Pb2+ in a sample of wastewater is to be determined by using
gravimetric analysis. To a 100.0-mL sample of the wastewater is added an excess of
sodium carbonate, forming the insoluble lead (II) carbonate (267.2092 g/mol) according to
the balanced equation given below. The solid lead (II) carbonate is dried, and its mass is
measured to be 0.4078 g. What was the concentration of Pb2+ in the original wastewater
sample?
What units do you want this. This often is reported in mg/L.
0.4078g PbCO3 x (molar mass Pb^2+/molar mass PbCO3) = ?g Pb and convert that to mg. That is mg/100 mL, convert to mg/L.
Pb^2+ =
To determine the concentration of Pb2+ in the original wastewater sample, we need to calculate the moles of lead (II) carbonate and then use stoichiometry to find the moles of Pb2+.
First, let's calculate the moles of lead (II) carbonate. We can use the molar mass of PbCO3 given (267.2092 g/mol) and the mass of the lead (II) carbonate measured (0.4078 g).
Moles of PbCO3 = Mass of PbCO3 / Molar mass of PbCO3
Moles of PbCO3 = 0.4078 g / 267.2092 g/mol
Next, we use the balanced equation to establish the stoichiometric relationship between PbCO3 and Pb2+.
The balanced equation is: PbCO3 + H2O -> Pb2+ + CO3^2-
From the equation, we see that 1 mole of PbCO3 produces 1 mole of Pb2+.
So, the moles of Pb2+ = Moles of PbCO3
Finally, to calculate the concentration of Pb2+ in the original wastewater sample, we need to consider the volume of the sample tested.
Concentration (C) is defined as moles divided by volume:
C = Moles of Pb2+ / Volume of wastewater sample
However, the volume of the wastewater sample is not provided in the question. Without that information, it is not possible to determine the exact concentration of Pb2+ in the original wastewater sample.