A classroom Experiment in Kit Form for Grades 9-‐12
Brief Background:
Students will learn the difference between reaction precipitates like the precipitation of basic copper carbonate from the reaction of copper chloride and sodium carbonate and those that result solely from a change in solution solubility (water vs. isopropanol). They will learn about precipitation in water treatment and purification and about the scientists who work to provide or maintain clean water for us. Additionally, students will learn that precipitates can sometimes be redissolved by adding another chemical compound and thus carrying out an additional chemical reaction.
Safety
Students and teachers must wear properly fitting goggles as they prepare for, conduct, and clean up from the activities in the kit. Read and follow all safety warnings. Also review the Materials Safety Data Sheets. Students must wash their hands with soap and water after the activities. The activities described in this kit are intended for students under the direct supervision of teachers.
Student kit packaged as 13 individual units for a class size of 26. Each student package is shared by 2 students.
Items in each 2-‐student Ziploc bag:
• (1) vial labeled “CuSO4” approximately 1/4 filled with cupric sulfate • (1) empty vial labeled “CuSO4 Solution” • (1) 4-‐mL vial labeled “CaCl2” containing small amount calcium chloride • (1) vial labeled “NaHCO3” (in red lettering) approximately 1/3 filled with sodium
Provide each 2-‐student team with the day’s experiment contained in the Ziploc bag (items in the bag are listed above) and 3 handouts (listed above). The items in the bag should be placed on the layout sheet as described below. Remove the 9oz cup labeled “water” from each bag and half-‐fill with water. Paper towels should be available for cleanup of spills. Each student must have a pen or pencil.
All students and instructors should have safety glasses and gloves.
1. What is a precipitate? a. A precipitate is an insoluble solid that emerges from a liquid solution. b. Precipitation may occur if the concentration of the solid exceeds its
solubility. c. It can also occur if two soluble salts react to form a third compound
that is insoluble.
2. Chemical change vs. solvent/solubility change a. Confirm worksheets and layout sheets are set up properly b. Tell students to keep pipets and scoops with their respective
solutions/chemicals and not to mix them up. c. Add 2 nearly full scoops of solid sodium bicarbonate to the
bicarbonate solution vial. d. Practice using the pipet to be able to add water dropwise. e. Add 2 mL of water using the pipet to the bicarbonate solution vial. f. Cap and shake vigorously to dissolve the bicarbonate.
i. A small amount will not dissolve ii. The solubility of bicarbonate in water is 100mg/mL and the
two scoops contain greater than 200 mg. g. Using a clean pipet, remove a few drops of clear liquid above the
remaining solid and add this to the vial containing isopropyl alcohol (IPA)
h. What happened? (should observe bicarbonate coming out of solution)
i. Enter results on worksheet under “test solution sodium bicarbonate IPA”.
j. Add 2 mL of water to the vial labeled CaCl2, calcium chloride k. Cap and shake to dissolve. (solution should be clear, no precipitate) l. Add 1 mL of additional water if it is not fully dissolved. m. Add a few drops of the clear supernatant solution in the bicarbonate
vial to the vial containing the CaCl2 solution. n. Observe (precipitate should form)
i. The equation shown below gives the specifics of the reaction between sodium bicarbonate and calcium chloride. These two compounds spontaneously react in water to form 4 different products, insoluble calcium carbonate, soluble sodium chloride, water, and carbon dioxide gas.
ii. Calcium carbonate is the compound used by ocean coral and marine plankton to build skeletons and for shellfish to build the shells they need for protection.
o. Record results on worksheet under “ test solution sodium bicarbonate
calcium chloride”.
3. Applications to real world issues: a. Purposeful precipitation is used to remove impurities from our
drinking water. b. These can be separated by filtration.
i. Rayfield Jackson is a water treatment chemist for the city of Chicago. As a water treatment chemist, Rayfield is just one of many types of scientists who work to provide or maintain clean water for all of us on the earth.
ii. Environmental Chemists work to limit human-‐caused damage to the environment. Hydrologists who study the movement, distribution, and quality of water on Earth and Wastewater Engineers who design systems that safely treat wastewater to remove harmful substances and return clean water back to the environment.
Alum is a class of compounds containing aluminum and sulfate. The 2 most common types of alum used are potassium alum and ammonium alum, and this slide shows you their chemical formula. Alum acts in two different ways to purify water. It causes suspended particles to clump together so they can be easily filtered out. It can also precipitate certain dissolved chemicals, like phosphates. Phosphates are potentially dangerous phosphorous salts that contaminate streams and lakes from the overuse of fertilizers. The removal of phosphate by alum is an example of a reaction precipitate.
4. Generating a precipitate: Copper salts-‐Copper carbonate. Solution Preparation
a. Examples of Copper Salts: when copper is exposed to the effects of weather, it develops a blue-‐green patina. The patina is a mixture of copper salts, including oxides, carbonates, and sulfides. Students are going to make what’s called basic copper carbonate from a solution of copper sulfate.
b. Using a clean scoop, place 4 full scoops of copper sulfate into the empty copper sulfate solution vial.
c. Using the measuring cup, measure 10 milliliters of water and add it to the copper sulfate.
d. Cap and shake to dissolve. Solution might remain slightly cloudy. This will not affect the experiment. Allow the vial to sit undisturbed for a few minutes to allow the undissolved particles to settle.
e. Using a clean scoop, place 2 scoops of sodium carbonate into the empty sodium carbonate solution vial.
f. Using the measuring cup, measure 5 milliliters of water and add it to the sodium carbonate.
g. Cap and shake to dissolve.
5. Experiments in minitubes-‐1 a. Bottom 3 tubes (4, 5, and 6) will get 6 drops each of copper sulfate
solution using a clean pipet. b. Add 1 drop of water into the first tube on the left (4). What happens?
(nothing-‐this will be the control well) c. Add 1 drop of sodium carbonate solution to the tube second from the
left (5). DO NOT MIX. Observe. (see light precipitate) d. Add 6 drops the sodium carbonate solution to the third tube (6) and
mix it gently with the toothpick for just a few seconds. (heavy precipitate and bubbles=CO2)
i. When copper sulfate reacts with sodium carbonate, it forms the precipitate basic copper carbonate.
ii. This is one of the main compounds present in the blue-‐green patina seen on the Statue of Liberty and weathered copper roofs and gutters.
When copper sulfate reacts with sodium carbonate, it forms the precipitate basic copper carbonate. This is a compound that contains 2 positively charged copper ions, 2 hydroxide ions, and a carbonate ion. It is insoluble in water and is one of the main compounds present in the blue-‐green patina seen on the Statue of Liberty and weathered copper roofs and gutters. In addition to this insoluble compound, the reaction also produces carbon dioxide gas, as you may have seen.
6. Isolation of basic copper carbonate a. Using the copper sulfate pipet, transfer about half of the remaining
copper sulfate solution to the empty unlabeled vial from the kit. b. Using the sodium carbonate pipet, add 15 drops of the sodium
carbonate solution into the unlabeled vial containing the copper sulfate solution. You should observe a thick precipitate forming. Gently swirl and allow it to settle.
c. Open the filter paper and place it over the small cup. d. Note color differences in different copper solutions. While all copper
salts are blue, each one has a slightly different hue. This is how we get the color variation seen in copper patina.
e. Using the copper sulfate pipet, try and suck up some of the precipitate
in the vial. f. Gently squeeze it out onto the middle of the filter paper over the cup.
Move the pipet around slightly so that the solid is not in a big clump, but is still in a small area so that later you can scoop it up with the spoon. Repeat if necessary to get more precipitate on to the filter paper.
g. Allow filtrate to dry for few minutes. h. Discuss next reaction steps in order to give filtrate sufficient time to
dry. i. Will be reacting copper carbonate with HCl to produce copper chloride (soluble) and CO2 (gas).
ii. Will also have a control well as before.
7. Experiment in mini-‐tubes-‐2 a. Using the top set of tubes working in in from left to right. b. Use the spoon and VERY GENTLY scrape some basic copper carbonate
precipitate onto the spoon. c. Using a toothpick, take a small portion of what’s there and transfer a
small portion to each of the three top tubes (1, 2, 3). Try to add the same amount to each tube.
d. Using the hydrochloric acid dropper, add 1 drop of acid to the first tube on the left (1).
e. Using a new toothpick, stir to see if the precipitate will dissolve. If not, add another drop and try again. If needed add a third drop and stir.
f. Record how many drops you used on your worksheet. g. Add the same number of drops of water to the second tube (2) as
hydrochloric acid you needed to dissolve the precipitate in the first tube. Stir and observe. (should not dissolve)
h. Using the hydrochloric acid dropper, add acid to the last tube (3) in order to dissolve the solid. Use the amount needed for the first tube as a guide, but DO NOT use extra. Add dropwise and stir with a clean toothpick after each drop.
We have a balanced equation – the quantity of each atom is the same on both sides of the equation. And now we are forming copper chloride, which is very soluble in water. And like before, we are causing the carbonate ion to become carbon dioxide gas. This means that once copper chloride forms, it cannot return to basic copper carbonate by itself because the carbonate has left the solution as carbon dioxide gas.
i. Once a clear or mostly clear solution is obtained, add 1 or 2 drops of sodium carbonate solution and observe. (a precipitate should form-‐basic copper carbonate Cu2(OH2)CO3)
Conclusions/Wrap up Students learned the difference between reaction precipitates like the basic copper carbonate we formed and those that result solely from a change in solution solubility. They learned about precipitation in water treatment and purification and about the scientists who work to provide or maintain clean water for us. Additionally, students learned that precipitates that form can sometimes be redissolved by adding another chemical compound. Students can be challenged to be able to provide balanced reactions for the experiments they performed and to be able to explain the observed precipitation reactions using solubility rules.
Cleanup:
All solutions can be disposed of by pouring down the laboratory sink with a large volume of water. Unused chemicals can be re-‐capped and saved for future use. Vials, cups and pipets can be rinsed, dried and re-‐used for subsequent experiments. Filter paper, toothpicks and other disposables should be discarded in the trash.
1. Chemical change vs. solvent/solubility change a. Confirm worksheets and layout sheets are set up properly b. Very Important! Pipets and scoops must be kept with their
respective solutions/chemicals and should not be mixed up. c. Add 2 nearly-‐full scoops of solid sodium bicarbonate to the
bicarbonate solution vial. d. Practice using the pipet to be able to add water dropwise. e. Add 2 mL of water using the pipet to the bicarbonate solution vial. f. Cap and shake vigorously to dissolve the bicarbonate. A small amount
of solid remaining is ok. g. Using a clean pipet, remove a few drops of clear liquid above the
remaining solid and add this to the vial containing isopropyl alcohol (IPA)
h. What happened i. Enter results on worksheet under “test solution sodium bicarbonate
IPA”. j. Add 2 mL of water to the vial labeled CaCl2 , calcium chloride k. Cap and shake to dissolve. l. Add 1 mL of additional water if it is not fully dissolved. m. Add a few drops of the clear supernatant solution in the bicarbonate
vial to the vial containing the CaCl2 solution. n. Observe o. Record results on worksheet under “ test solution sodium bicarbonate
calcium chloride”. 2. Generating a precipitate: Copper salts-‐Copper carbonate. Solution
Preparation a. Using a clean scoop, place 4 full scoops of copper sulfate and into the
empty copper sulfate solution vial. b. Using the measuring cup, measure 10 milliliters of water and add it to
the copper sulfate. c. Cap and shake to dissolve. Solution might remain slightly cloudy.
This will not affect the experiment. Allow the vial to sit undisturbed for a few minutes to allow the undissolved particles to settle.
d. Using a clean scoop, place 2 scoops of sodium carbonate into the empty sodium carbonate solution vial.
e. Using the measuring cup, measure 5 milliliters of water and add it to the sodium carbonate.
f. Cap and shake to dissolve. 3. Experiments in minitubes-‐1
a. Bottom 3 tubes (4, 5, 6) will get 6 drops each of copper sulfate solution using a clean pipet.
b. Add 1 drop of water into the first tube on the left (4). What happens? c. Add 1 drop of sodium carbonate solution to the tube second from the
d. Add 6 drops the sodium carbonate solution to the third tube (6) and mix it gently with the toothpick for just a few seconds. Observe.
e. Enter results and observations on worksheet. 4. Isolation of basic copper carbonate
a. Using the copper sulfate pipet, transfer about half of the remaining copper sulfate solution to the empty unlabeled vial from the kit.
b. Using the sodium carbonate pipet, add 15 drops of the sodium carbonate solution into the unlabeled vial containing the copper sulfate solution. You should observe a thick precipitate forming. Gently swirl and allow it to settle.
c. Open the filter paper and place it over the small cup. d. Note color differences in different copper solutions. e. Using the copper sulfate pipet, try and suck up some of the precipitate
in the vial. f. Gently squeeze it out onto the middle of the filter paper over the cup.
Move the pipet around slightly so that the solid is not in a big clump, but is still in a small area so that later you can scoop it up with the spoon. Repeat if necessary to get more precipitate on to the filter paper.
g. Allow filtrate to dry for few minutes. 5. Experiment in mini-‐tubes-‐2
a. Using the top set of tubes working in in from left to right (1, 2, 3). b. Use the spoon and VERY GENTLY scrape some basic copper carbonate
precipitate onto the spoon. c. Using a toothpick, take a small portion of what’s there and transfer a
small portion to each of the three top tubes (1, 2, 3). Try to add the same amount to each tube.
d. Using the hydrochloric acid dropper and add 1 drop of acid to the first tube on the left (1).
e. Using a new toothpick, stir to see if the precipitate will dissolve. If not, add another drop and try again. If needed add a third drop and stir.
f. Record how many drops you used on your worksheet. g. Add the same number of drops of water to the second tube (2) as
hydrochloric acid you needed to dissolve the precipitate in the first tube. Stir and observe.
h. Using the hydrochloric acid dropper and add acid to the last tube (3) in order to dissolve the solid. Use the amount needed for the first tube as a guide, but DO NOT use extra. Add dropwise and stir with a clean toothpick after each drop.
i. Once a clear or mostly clear solution is obtained, add 1 or 2 drops of sodium carbonate solution and observe.
Cleanup: All solutions can be disposed of by pouring down the laboratory sink with a large volume of water. Vials, cups and pipets can be rinsed, dried and re-‐
Acknowledgements: This experiment was developed in collaboration with the American Chemical Society and is derived from experiments contained in “Chemistry-‐Investigating Your World” in the IYC 2011 book. Further information can be found at www.acs.org/iyckit. Their support is gratefully acknowledged.
