Determination of the empirical formula of basic
copper carbonate
Background:
There are two different formulas for basic copper carbonate, Cu2(OH)2CO3 and
Cu3(OH)2(CO3)2. In this experiment we will determine which of theses two forms we
are working with in the lab. In part one we will determine the percent carbon
dioxide present in the original sample. In part two we will determine the percent
copper present in the compound.
Part I:
The addition of hydrochloric acid (HCl) to copper carbonate dissolved in water will
result in the production of carbon dioxide gas. This reaction will be used to
determine the percent carbonate in the original sample
Copper Carbonate + Hydrochloric acid --> Copper chloride + Carbon dioxide + water
Part II:
The concentration of a solution is determined by how much of the solute (stuff being
dissolved) is dissolved. We can estimate the concentration of colored solutions by
comparing their color. This method will be use to calculate the percent copper in the
original sample.
Materials:
Basic Copper Carbonate, 2g
Pipets
Copper (II) sulfate stock solution
Test tube
Hydrochloric acid solution
Unknown basic copper carbonate solution
Distilled water
Balance
Erlenmeyer flask
Graduated cylinders, 10 ml and 20 ml
Safety: Hydrochloric acid solution is toxic and corrosive to eyes and skin. Copper
carbonate is slightly toxic by ingestion and inhalation. Wear chemical splash goggles,
chemical resistant gloves, and a chemical resistant apron. Wash hands thoroughly
with soap and water before leaving the laboratory. Please follow all laboratory safety
guidelines.
Procedure:
Part I:
1.) Record the mass of one 125-mL Erlenmeyer flask and record the value in your
data table,
2.) Using weighing paper measure out about 0.15 g of the basic copper carbonate
sample and add it to your flask. Record the new weight of your flask in your data
table.
3.) Use a 25-mL graduated cylinder to obtain 15 mL of hydrochloric acid. Measure
and record the combined mass of the cylinder and acid.
4.) SLOWLY pour the hydrochloric acid into the Erlenmeyer flask. Allow the
reaction of the HCl and the copper carbonate to go to completion. Measure and
record the mass of the empty cylinder after adding the HCl to the flask.
5.) Once the reaction appears complete, GENTLY swirl the flask to allow any further
reaction to take place.
6.) Measure and record the mass of the Erlenmeyer flask and its new contents.
Part 2:
1.) Using a 10-mL graduated cylinder measure out exactly 10.0 mL of the unknown
basic copper carbonate solution.
2.) Using the solutions in the test tubes provided by the teacher compare the color of
the unknown solution to the color of one of the solutions in the test tubes. Once you
find a color match record the amount of copper in the unknown solution in your
data table.
Data table:
Mass of clean dry Erlenmeyer flask
Mass of Erlenmeyer flask and metal carbonate sample
Mass of metal carbonate
Mass of graduated cylinder and HCl
Mass of cylinder after HCl was added to flask
Mass of HCl added to sample
Mass of flask + metal carbonate + HCl
Mass of flask + Final solution after loss of CO2
Mass of CO2 released
Percent CO2 in metal carbonate sample
Estimated mass of copper in unknown solution