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The Determination of a Chemical Formula Lab Report

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lindsey pitts

on 16 November 2014

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Transcript of The Determination of a Chemical Formula Lab Report

Percent Error Calculation for Copper
Percent Composition of Copper= Molar mass of copper
Molar mass of CuCl2*2H2O
.372= 63.55 g Cu
170.48 g CuCl2*2H2O

Theoretical Mass of Cu= Mass of hydrated sample*Percent Comp
.3803 g Cu=1.02 g Cu*.3728

% Error= Theoretical-Actual *100

39.52%= .3803-.23 *100
Error Discussion
The percent error for Copper was 39.52%. This is relatively high, however it is less than 50% so it is not terrible. One reason the error may have been so high is the fact that not all of the copper may have been transferred from the beaker to the filter paper. When we first began transferring the copper we started by scooping it out of the beaker. This could have resulted in the loss of some of the copper, causing the percent error to be high. It would have been higher if it weren't for our realization that we were supposed to pour the entire beaker onto the filter paper in the funnel.
The End (:
Data Analysis
How many moles of water were in your sample of copper chloride hydrate?
.25g H2O * 1 mol H2O/18.02g H2O = .01387 mol H2O
How many moles of copper were in your sample of copper chloride?
.23g Cu * 1 mol Cu/63.55g Cu = .00362 mol Cu
How many moles of chlorine were in your sample of copper chloride?
.54g Cl * 1 mol Cl/35.45g Cl = .01523 mol Cl
Write the proper chemical formula for the compound you tested.
Based off of our results: CuCl4 * 4H20
What it should be: CuCl2 * 2H2O

Determine the water of hydration in a copper chloride hydrate sample
Conduct a reaction between a solution of copper chloride and solid aluminum
Use the results of the reaction to determine the mass and moles of Cu and Cl in the reaction
Calculate the empirical formula of the copper chloride compound
The Determination of a Chemical Formula Lab Report
Steps 1-3:
Set up
1. Obtain and wear goggles
2. Measure and record the mass of a clean, dry crucible without cover. Obtain about 1 gram of the unknown copper chloride hydrate and place it in the crucible. Use a spatula to break up any large pieces of the substance by pressing the pieces against the wall of the crucible. Measure and record the mass of the crucible with compound.
3. Set up a ring stand, ring, and clay triangle for heating the sample. Rest the crucible on the clay triangle. Set up a lab burner and ignite the burner away from the crucible. Adjust the burner to get a small flame.
Data Table
Mass of crucible (g) 13.51
Mass of crucible and hydrated sample (g) 14.53
Mass of hydrated sample (g) 1.02
Mass of crucible and dehydrated sample (g) 14.28
Mass of dehydrated sample (g) .77
Mass of water evolved (g) .25
Mass of filter paper (g) 1.00
Mass of filter paper and copper (g) 1.23
Mass of copper (g) .23

Lindsey Pitts, Nicole Bell, Jessica League
Steps 4-9:
4. Hold the burner in your hand and move the flame slowly back and forth underneath the crucible to gently heat the sample. Do not overheat the compound. Note the color change, from blue-green to brownish, as the water of hydration is driven out of the crystals. When the sample has turned brown, gently heat the crucible for two more minutes.
Crucible with cover
Crucible tongs
Ring stand, ring, and clay triangle
Lab burner
Filter paper
Unknown solid copper chloride hydrate
Aluminum wire, 20 gauge
6 M hydrochloric acid, HCL, solution
95% ethanol solution
Distilled water
Wash bottle
Glass stirring rod
5. Remove and turn off the burner. Cover the crucible and allow the sample to cool for about ten minutes.
6. Remove the crucible cover and inspect your sample. If you see any blue-green crystals, reheat the sample until the crystals have turned brown.
7. Measure and record the mass of the cool crucible of your copper chloride sample.
8. Transfer the brown solid to a clean and empty 50 mL beaker. Rinse out the crucible with two 8 mL aliquots of distilled water and pour the water into the 50 mL beaker. Gently swirl the beaker to completely dissolve the solid. Note that the color of the solution is green as the copper ions are rehydrated.
9. Measure out about 20 cm of aluminum wire, coil the wire, and place the wire in the beaker of solution so that it is completely immersed in the copper chloride solution. Note that the reaction produces a gas, elemental copper is forming on the surface of the aluminum wire, and the color of the solution is fading. The reaction will take about 30 mins to complete.
Steps 10&11
10. When the reaction is done, the solution will be colorless. Most of the elemental copper will be on the aluminum wire. Add 6 drops of 6 M HCl solution to dissolve any insoluble aluminum salts in the mixture, which should make the solution clear.
11.Use a glass stirring rod to scrape off as much copper as possible from the Al wire. Slide the wire up the wall of the beaker up and out of the solution with the glass stirrer and rinse off any remaining copper with distilled water. if any of the copper refuses to wash off the aluminum wire, wash it with one or two drops of 6 M HCl solution. Put the Al wire aside.
Steps 12:
12. Collect and wash the copper produced in the reaction.
a. Set up a funnel for filtration
b. Obtain a piece of filter paper. Measure and record its mass, and then place the filter paper on the funnel. Start the filtration.
c. Use small amounts of distilled water to wash all of the copper onto the filter paper on the funnel. Use the glass stirring rod to break up the larger pieces of copper.
d. Wash the copper twice more with small amounts of distilled water.
Steps 13-15
13. Remove the filter paper with the copper from the funnel and leave it to dry.
14. When it has dried measure and record the mass of the filter paper and copper.
15. Dispose of the copper, aluminum wire, and filtered liquid as directed.
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