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Discuss how your supernatant color in the 6 different test tubes supports your calculated result in #2. For example, if you used less than the volume of sodium phosphate calculated in #2, what would be the limiting reactant and does the observed supernatant color support this.
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0) The sodium phosphate, Na3PO4 solution has NPFA ratings of 1 (out of 4) for health, 0 for fire, and 0 for reactivity. Cobalt (II) nitrate has 2 for health, 0 fire, and 0 for reactivity. 1) Carefully label (1-‐6) and weigh 6 small test tubes. 2) You will need 20 mL of 0.12 M sodium phosphate and two disposable pipettes. To each test tube use the pump dispenser to add 3.0 mL of 0.10 M cobalt (II) nitrate. Then use a buret to add the following amounts of 0.12 M sodium phosphate. Record the initial and final volumes to the 0.01 mL. Any recorded volume not recorded to the hundredth of a mL will be penalized. Test tube 1 will have about 0.50 mL of sodium phosphate, test tube 2 will have 1.0 mL, test tube three will have 1.5 mL, test tube 4 will have 2.0 mL, test tube 5 will have 2.5 mL, and test tube 6 will have 3.0 mL. Mix the tube contents using a vortex mixer, and centrifuge the mixture for five minutes (or until the solid is separated from the supernatant liquid that lies above the solid material). In a table like the following (which might look better in landscape mode), record your observations about the solid material formed and the supernatant color. Save the leftover sodium phosphate.
Lab_6_CoPO4_LR S_2015 Page 2
Test Tube #
Mass of empty tube/g
Initial Buret Volume/mL, 0.12 M sodium phosphate
Final Buret Volume/mL, 0.12 M sodium phosphate
Volume sodium phosphate added/ mL
1 3. On a spot plate, use a Sharpie pen to label the wells from 1-‐6. Use a disposable pipette to add several drops of supernatant liquid from each test tube to a well. Rinse the pipette between samples of supernatant liquid, and rinse the pipette several times before the next step. 4. You will need another milliliter of cobalt (II) nitrate. To each sample of supernatant drops on the spot plate, add two drops of the original cobalt (II) nitrate solution. Draw a table similar to below leaving plenty of room to record your observations in your notebook. Rinse the pipette and rinse and dry the spot plate before the next step. 5. Add several drops of the supernatant to each of the 6 wells in the spot plate, and then add two drops of the original sodium phosphate solution to each. Record your observations in your notebook. Rinse and dry the spot plate when finished. Test Tube #Supernatant => 1 2 3 4 5 6 Supernatant observations after adding Co (NO3)2 Supernatant observations after adding Na3PO4 6. Carefully decant the remaining supernatant liquid out of each tube into an appropriate waste container. Try not to disturb or lose any of the precipitate in the tubes. 7. Add 3 mL of distilled water to each tube and mix with vortex. Centrifuge each and decant. This is called washing the precipitate. 8. Repeat step 7 and then put the 6 test tubes in a small beaker labeled with your lab section and you and your partners initials, and put in an oven to dry overnight. 9. In the next lab period, remove the test tubes, cool and weigh. Record your data in
Calculations The following shows the calculation of the mass of cobalt (II) phosphate produced from 3.0 mL of cobalt (II) nitrate. This calculation assumes a 2/1 ratio between cobalt phosphate and cobalt (II) nitrate and uses the formula of CoPO4, and molar mass of 129.56 for cobalt (II) phosphate. All of these assumptions are incorrect. The student needs to use the correct ratio, molar mass and formula. The first step has converted 0.10 M, (or 0.10 moles/Liter) into 0.10 moles/1000 mL. 3.0 𝑚𝐿 𝐶𝑜𝐼𝐼𝑛𝑖𝑡𝑟𝑎𝑡𝑒 𝑋!.!" !"# !"!!!"#!"#$ !""" !" 𝑋! !" !"! ! !" !"!!𝑋!"#.!" ! !"#$! ! !"# !"#$! = g Co PO4 You will do similar calculations for each volume of sodium phosphate. By comparing the theoretical yield of product from cobalt (II) nitrate versus sodium phosphate, you can predict how much product was made. Report This report will follow the outline given on MOODLE for a formal report. IN ADDITION TO FOLLOWING THE MOODLE DOCUMENT’S RESULTS FORMAT, please include the following in the order given in your discussion of results. 1) Balance the electrical charges in the products, then balance the equation. Neatly write the equations as a) The molecular equation, labeling the physical states (s, L, g, aq) of all reactants and products. b) The ionic equation, labeling the physical states, and electric charge of all ions. c) The net ionic equation, labeling the physical states, and electric charge of all ions. d) Briefly justify your choice of precipitate. 2) Use your balanced equation to calculate the volume of 0.12 M Na3PO4 to stoichiometrically react with the 3.0 mL of Co (NO3)2. Show your work.
Lab_6_CoPO4_LR S_2015 Page 4
3) Discuss how your supernatant color in the 6 different test tubes supports your calculated result in #2. For example, if you used less than the volume of sodium phosphate calculated in #2, what would be the limiting reactant and does the observed supernatant color support this. 4) Calculate the theoretical yield of solid precipitate if the 3.0 mL of Co (NO3)2 limits the reaction. Show your work. 5) Calculate the theoretical yields of solid precipitate if the different volumes of 0.12 M Na3PO4 limits the reactions. You only need to show your work for the 0.5 mL reaction and show your calculated results for the other 5 calculations. Use your experimentally measured volumes of sodium phosphate. 6) Include a graph of students’ experimental precipitate mass versus volume of sodium phosphate, and discuss how the mass of precipitate should change as volume of sodium phosphate increases. Comment on if the data supports your calculated result in #2. Discuss how the formation of product hydrates would affect the data. 7) Your conclusions should tie together and summarize the supernatant color, supernatant test, product mass and the balanced equation.