Chapter 1. Experiment 3
Synthesis of Copper(II) Saccharinate
Purpose of the Experiment
To synthesize a bioinorganic compound from its two constituents and determine the theoretical, actual and percent yields of the reaction.
Background Required
This experiment will use basic laboratory techniques of weighing by difference and tare weighing, and vacuum filtration method. The concepts of stoichiometry, theoretical yield, actual yield, and percent yield are used in this experiment.
Background Information
Very few of the chemicals we use in daily life are found “as is” in nature. So almost all chemicals used today are made or synthesized from other chemicals. Chemists work to synthesize new compounds to use in studying how chemicals react, in producing a compound for industrial use, or in producing compounds that ultimately are used by the public. A significant portion of chemistry concerns studying chemical reactions. So this laboratory experiment is an introduction to a simple synthesis. You will also develop the laboratory techniques and skills needed to produce and recover a solid product.
Saccharin is one of the first artificial sweeteners and is 300 times “sweeter” than sucrose. In 1975, a preliminary study showed that large amounts of saccharin in mice caused bladder cancer. This caused a ban on saccharin by FDA until 1991. The ban was lifted when further studies failed to show that it caused cancer. Saccharin is now found in several artificial sweeteners, such as Sweet’N Low™ and NutraSweet™. Now scientists are investigating copper saccharinate complexes for anti-cancer and antimicrobial activities.
The compound that will be made today involves sodium saccharin, NaC7H4SO3N, binding to Cu+2 ions. The formula of the product is Cu(saccharinate)2(H2O)4·2 H2O and is also written as [Cu(C7H4SO3N)2(H2O)4]·2 H2O. For this experiment, we will simply call it, copper(II) saccharinate. It consists of two saccharin molecules, bonding to the Cu+2 ion through the lone pair of electrons on the N atom in saccharin. In addition, 4 H2O molecules are also bound directly to the Cu+2 ion through a lone pair of electrons on the O atoms of the water molecules. Two other water molecules are found in the crystals as water of hydration (not directly bound to the Cu).
The actual yield (or experimental yield) is amount of product recovered in the experiment. The theoretical yield is the amount of product that could be produced from the limiting reagent if the reaction were 100% efficient. This amount is calculated from the limiting reagent or reactant. The percent yield is the ratio of the actual yield to the theoretical yield.
In This Experiment
In this experiment, the synthesis of the copper(II) saccharinate occurs in a single reaction.
Cu+2(aq) + 2 C7H4SO3N–(aq) + 4 H2O(ℓ) → Cu(C7H4SO3N)2(H2O)4·2 H2O(s)
Upon adding the solution of saccharin to the Cu+2 solution, some of the product may form immediately. However, in order to obtain a more crystalline product, a digestion procedure is followed where first the solution is heated. (This dissolves any product that has formed and continued heating reduces the volume making the solution more concentrated.) Then the solution is slowly cooled, first to room temperature and then in an ice-bath. The slow cooling promotes formation of crystals instead of a powder. In general, crystals have less contaminants, are purer than powders, and easier to filter. Finally, the product is filtered by connecting a side-arm flask with vacuum tubing to a water aspirator and placing a Büchner funnel in the mouth of the flask. When the water is running, this creates a vacuum to facilitate filtering and drying of the solid. The product is insoluble in cold ethanol, so the product is rinsed with cold ethanol to remove any remaining water. Once the product is dried, you will determine the actual yield. Using the theoretical and actual yield, you will determine the percent yield of the copper(II) saccharinate.
Example:
Problem
What is the theoretical, actual, and percent yield for the synthesis of the Cu(C7H4SO3N)2(H2O)4·2 H2O(s) when starting with 4.00 g of Cu(C2H3O2)2·H2O and 9.00 g of NaC7H4SO3N·H2O and obtaining 8.37 g of crystalline product?
Solution
(1) You will need to first determine the theoretical yield of the product using the mass of the reactants, their molar mass, and the reaction stoichiometry. To do this, you will need the molar mass of each reactant. Both of the reactants have a water of hydration which is shown by the “·H2O” at the end of the chemical formulas. So we must add the weight of water to the overall molar mass. Then calculate the moles of both the copper(II) acetate and the sodium saccharinate.
Since the mole ratio of NaC7H4SO3N·H2O to Cu(C2H3O2)2·H2O is 2:1, the experiment needs at least 0.0400 moles of NaC7H4SO3N·H2O. Since there is slightly more than 0.0400 moles, the copper(II) acetate is the limiting reagent.
(2) Next, the actual yield is the experimental yield or how much product did the experiment produce.
Actual yield = 8.37 g of Cu(C7H4SO3N)2(H2O)4·2 H2O
(3) The percent yield is the (actual yield/theoretical yield) x 100%.
Procedure
Always Wear Safety Goggles and Use Good Lab Practices
Chemical Alert:
Part I
Preparing Reactants
1. Tare the weight of the weigh boat to zero.
Add Cu(C2H3O2)2·H2O powder to the weigh boat until you obtain a mass that is approximately 2.00g.
Record this exact mass and your observation about the solid.
2. Add approximately 25 mL of deionized water to a 150 mL beaker.
Transfer the powder to the beaker. Discard the weigh boat into the trash can.
3. Place the beaker on a hot plate. Heat the solution with constant stirring until the solid completely dissolves. Leave the beaker on the hot plate.
Record your observation about this solution.
4. Tare the weight of a new weigh boat to zero.
Add small amounts of sodium saccharinate until you have obtained approximately 4.50 g.
Record your exact mass and your observation about the solid.
5. Add approximately 25 mL of deionized water to a 50 mL beaker.
Add the sodium saccharinate to this beaker.
Using a glass stirring rod, stir the solution until all of the solid has dissolved. Record your observations.
Part II
Reaction
6.Pour the solution of sodium saccharinate into the hot solution of copper(II) acetate solution. Rinse the sodium saccharinate beaker with water from your wash bottle to rinse all of the solution into the reaction in the reaction beaker.
7.Continue to heat and gently boil the solution for about 10 minutes.
8.Carefully remove the beaker and place on the lab bench. (The beaker is HOT!) Turn off the hot plate.
Do not disturb or agitate the solution.
Part III
Crystallizing and Recovering the Cu(C7H4SO3N)2(H2O)4·2 H2O
9. Prepare an ice bath in a 400 mL beaker by filling the beaker about half full with ice and adding about 50 mL of water.
10. After the beaker with the mixture cools down to room temperature, place the beaker into the ice bath.
11. Leave the reaction mixture undisturbed in the ice bath for about 25 minutes. You should see some crystals form by this time. Record your observations.
12. While waiting for the crystals to form, pour 5 mL of 95% ethanol in a test tube. Place the test tube in the ice bath.
Set up the vacuum filtration apparatus as seen below.
13. Place a piece of filter paper in the Büchner funnel.
Completely moisten the filter paper by squirting a little water from your wash bottle. Turn on the water to begin vacuum filtration.
14. Scrape the sides and bottom of the beaker to loosen the crystals.
Pour the mixture into the Büchner funnel.
If needed, use your stirring rod to scrape any remaining crystals into the funnel.
15. Rinse the crystals by pouring about half of the cold 95% ethanol onto the crystals. Follow with a second rinse with the remaining cold ethanol.
Continue the vacuum to pull air through the crystals to dry the crystals.
When the crystals and paper appear dry, remove the hose to the water aspirator and then turn off the water.
16. Weigh a clean watch glass using the weighing by difference technique. Record its mass.
Scrape all the crystals off the filter paper onto the watch glass and reweigh.
Record the mass of crystals 1 watch glass.
17. Pour the contents of the filter flask and the crystals in the appropriate waste containers located in the hood.
Throw away the filter paper in the trash can.
Wash and put away all glassware and equipment.
ALWAYS WASH YOUR HANDS AFTER FINISHING AN EXPERIMENT.
Calculations
Calculate the theoretical yield of Cu(C7H4SO3N)2(H2O)4·2 H2O.
Calculate the percent yield of the Cu(C7H4SO3N)2(H2O)4·2 H2O.
Discussion
1.Summarize the results of this experiment. What did you set out to do in the purpose of the experiment – what is the actual, theoretical and percent yields?
2.What is the quality of the results? Do the results seem reasonable? Examining the percent yield, does it seem low or high?
3.What were the errors or possible errors in the experiment?
4.List any errors or problems in the procedure. Also list some possible errors in the experiment. Example: Did some of the crystals remain behind in the beaker? Were there any problems in getting the crystals to form?
5.How would the errors affect the results of the experiment? Example: If some of the crystals were left behind in the beaker, then the actual yield is lower than it should be. Therefore the percent yield will be lower since it is the actual yield (low)/theoretical yield.
Study Questions
1.Which chemical(s) used in this experiment are corrosive?
2.Which is the mole to mole ratio between Cu+2 and saccharin?
3.What is the molar mass of the product?
4.Cooper & Zach did this experiment starting with 1.1 g of Cu(C2H3O2)2·H2O and an excess of sodium saccharinate. They recovered 2.46 g of the copper(II) saccharinate product.
a)What is their actual yield?
b)What is their theoretical yield?
c)What is their percent yield?
5.Copper(II) saccharinate product is insoluble in cold ethanol, slightly soluble in warm ethanol, and very soluble in hot water. The procedure called for rinsing the crystals in cold ethanol, since the crystals will not dissolve.
Using this information, explain what affect each of the following will have on the actual yield of the product?
a)Washing the Cu(C7H4SO3N)2(H2O)4·2 H2O crystals with warm ethanol.
b)Washing the Cu(C7H4SO3N)2(H2O)4·2 H2O crystals with hot water.
c)Only cooling the reaction mixture to room temperature (not using the ice-bath).
6.Explain what affect each of the following will have on the percent yield of the copper(II) saccharinate product.
a)Some crystals were left behind on the filter paper.
b)Spilled some of the reaction mixture while heating it on the hot plate.
c)Forgot to tare the balance (subtracting out the weight of the weigh boat) when weighing the Cu(C2H3O2)2·H2O. (The initial mass of the Cu(C2H3O2)2·H2O is less than the recorded mass.)
7.If you weigh the Cu(C7H4SO3N)2(H2O)4·2 H2O crystals while they are still wet, will this affect your actual yield? If so, explain how.
8.In theory, is it possible to have a percent yield greater than 100%? Can errors create a percent yield that is greater than 100%? What kind of errors might lead to a having a percent yield greater than 100%?
Activity Completed!