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# Background An empirical formula describes the simplest ratio for of each type of atom that a compound contains, whereas the molecular formula gives...

Question:

Use: Experiment 2 Notes in the attachment for this:

1. Record and calculate the following about the copper sulfate pentahydrate

 a Mass of CuSO4*5H2O (g) b Molecular weight of CuSO4*5H2O c Moles of CuSO4*5H2O d Moles of Cu in the copper sulfate salt:

2. Calculate the following for the oxygen:

 a The initial mass of copper in the moles of copper from the copper sulfate salt (MW of Cu = 63.55 g/mole) (g) b The mass of copper oxide obtained (g) (the mass of the copper oxide in the test tube after heating over Bunsen burner to remove water) c The gain in mass, equal to the added mass of oxygen (g) d The number of moles of oxygen in the copper oxide, given a molecular weight of oxygen (O) equal to 16.00 g/mole

3. Calculate the molar ratio of copper to oxygen from:

(moles copper) / (moles of oxygen in the copper oxide)

4. According to this molar ratio, what is the empirical formula of copper oxide?

5. Calculate the yield of copper oxide:

a) Expected number of moles of copper oxide (using the empirical formula of copper oxide and the starting moles of Cu)

b) Actual mass of copper oxide (g)

c) Actual moles of copper oxide (dividing the mass by the MW of the copper oxide)

6. Calculate the percent difference between the expected and actual values for the moles of copper oxide, according to the following equation:

% difference = |expected moles - actual moles| / expected moles * 100%

7. Is there a percent difference between your actual and expected? If there was a difference, what could account for this difference?

Background An empirical formula describes the simplest ratio for of each type of atom that a compound contains, whereas the molecular formula gives the actual number of atoms in that compound. The empirical formula of a compound can be derived by finding the number of moles of the elements in a sample compound and then determining the simplest ratio between them. The molar ratio represents the simplest ratio for the number of moles of each element in a particular compound rather than the total number of moles in the compound. In this lab we will form copper oxide using two methods. The first method is simply to heat dry copper powder until it combines with oxygen in the air. Comparing the mass of copper to the mass of copper oxide allows us to determine the ratio of copper to oxygen in the compound. The second method uses an aqueous solution of copper(II) sulfate (CuSO ) combined with sodium hydroxide (NaOH) which yields a copper hydroxide precipitate. This precipitate is then heated until a decomposition reaction yields water vapor and copper oxide. Since we know exactly how much copper sulfate we begin with, is possible to calculate the molar quantity of copper oxide that is formed and then determine its empirical formula. 4
Procedures Experiment 1 1. Place a clean crucible from the Containers shelf onto the workbench. 2. Place a balance and Bunsen burner from the Instruments shelf onto the workbench. 3. Move the crucible onto the balance and record the mass of the crucible in your notes. 4. Move the crucible onto the workbench and add 10 g of copper (Cu) from the Materials shelf into it. 5. Move crucible onto the balance and record the combined mass of the crucible plus copper in your notes. Does the number make sense? 6. Move the crucible onto the Bunsen burner. Double-click the crucible to open its properties. Select Show Contents and click OK . (This cut-away gives you a view of the Crucible's contents.) 7. Turn on the Bunsen burner and set the flame to low. To turn on the burner, click on the black knob. (Clicking multiple times will increase the intensity of the flame until it is turned off.) 8. Start the Timer by clicking on the clock icon in the lower left of the window frame. 9. The copper will react with the oxygen in the air. You will see the contents of the crucible change color, signifying that the reaction is complete. Watch the crucible for an additional 30 – 60 seconds to verify that no further reactions occur. (You may want to use the + or zoom buttons in the lower right of the screen for a closer view.) 10. Move the crucible onto the workbench to cool and turn off the Bunsen burner. 11. Weigh the crucible and its contents. Record the total mass. (Remember to press Save Notes so you don't lose your calculations.) Did the mass of the crucible's contents increase or decrease? 12. Clear the workbench by dragging your containers to the recycling bin beneath the workbench. Experiment 2 1. Place a 50 mL beaker from the Containers shelf onto the balance. Record the mass. 2. Move the beaker onto the workbench and add 5 g of copper sulfate pentahydrate (CuSO *5H O) from the Materials shelf. 3. Weigh the beaker and record the combined mass of the beaker and its contents in your notes. 4. Dissolve the copper sulfate pentahydrate by adding 30 mL of water to the beaker. Note: In a conventional wet lab, you would remove the container from the balance before you add any chemicals or 4 2
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1. Record and calculate the following for the copper:
(a) The mass of copper powder used (g)
10 g
(b)The number of moles of copper powder (g), given a molecular weight of copper equal to 63.55...

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