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Determining the Empirical Formula of Copper Chloride

Determining the Empirical Formula of Copper Chloride. Purpose of the Experiment Determine the empirical formula of a compound containing only copper and chlorine. Molar Mass (Molecular Weight). The mass in grams of 1 mole of a compound. H 2 O MW = 18.0148 g AlCl 3 MW= 133.341 g.

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Determining the Empirical Formula of Copper Chloride

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  1. Determining the Empirical Formula of Copper Chloride Purpose of the Experiment Determine the empirical formula of a compound containing only copper and chlorine

  2. Molar Mass (Molecular Weight) The mass in grams of 1 mole of a compound H2O MW = 18.0148 g AlCl3 MW= 133.341 g

  3. Percent Composition Gives the percentages of a compound’s mass that are due to each of the component elements C2H5OH Mass of C = 24.022 g Mass of H = 6.048 g Mass of O = 15.999 g Mass of 1 mole of C2H5OH = 24.022 + 6.048 + 15.999 = 46.069

  4. Empirical Formula Represents the simplest whole-number ratio of the various types of atoms in a compound Examples: CH5N , C2H10N2, C3H15N3

  5. Schematic diagram of the combustion device used to analyze substances for carbon and hydrogen.

  6. Empirical Formula Example A white compound is analyzed and found to contain 43.64% phosphorous and 56.36% oxygen by mass. What is the empirical formula? In terms of moles, in 100.00 g of compound we have: 43.64g P x (1 mol P / 30.97g P) = 1.409 mol P 56.36 g O x (1 mol O / 15.99g O) = 3.523 mol O

  7. 1.409 3.523 1 P and 2.5 O = = 1.409 1.409 Empirical Formula Example, contd. Dividing both mole values by the smaller one gives: This yields the formula PO2.5 Since compounds must contain whole numbers of atoms, the empirical formula should contain only whole numbers. Empirical Formula = P2O5

  8. Atmospheric oxygen in excess heat Mg(s-silvery-white) + O2(g) MgxOy(s, white) (0.353 g) limiting reagent Result: Mass of MgxOy = 0.585 g Another Empirical Formula Example

  9. Mass of O = total mass of compound – mass of Mg = 0.232 g Another Empirical Formula Example, contd. Mg = 60.3% and O = 39.7%

  10. Mg = 60.3% and O = 39.7% Formula masses and percent composition of three theoretical compounds of Mg and O Formula of Oxide MgxOy %Mg %O 60.3% 39.7% MgO 43.2% 56.8% MgO2 Mg2O 75.2% 24.8%

  11. Today’s Experiment Original Zn(s, silvery white) + CuxCly(aq, blue) ZnCl2(aq) + Cu(s, reddish) Modified Al(s, silvery white) + CuxCly(aq, blue) AlCl3(aq) + Cu(s, reddish) ~0.3 g ea. strip (excess) 25 mL Limiting reagent known mass known mass

  12. Copper is a transition metal, with unfilled d orbitals. Ground state electron configuration: [Ar].3d10.4s1 Shell structure: 2.8.18.1 Transition metals may exhibit multiple oxidation states (+1, +2, +3, etc…). These are not easily predicted by position in the periodic table. Transition metals ions in aqueous solutions frequently are brightly colored, also due to d orbitals (e.g. Cu ions are blue).

  13. Zn and Al are both stronger reducing agents than copper. (Note: the redox potentials on next slide) Because of this either one would work to produce metallic copper from a solution of a copper salt.

  14. * * * These potentials indicate the relative thermodynamic tendency for the indicated half-reaction to occur.

  15. Other Reactions in the Procedure: Removal of Excess Reducing Agent Zn(s) + 2 HCl(aq) ----> ZnCl2(aq) + H2(g) 2 Al(s) + 6 HCl(aq) ----> 2 AlCl3(aq) + 3 H2(g) Cu(s) + n HCl(aq) --x--> No Reaction

  16. Checkout 2 pc Al foil (~0.3 g) 1-pr Beaker Tongs Reagents in Lab CuClx solution in 4L spigot jugs - take ~25 ml for each run Record data: (0.08067 g CuClx / ml, d=1.074 g/ml) 10% HCl in 1L wash bottles (take ~5 ml) (N.B. solid NaHCO3 is to be used for acid spills)

  17. Add Al foil 25 mL copper chloride, weigh and use exact density to get mass of CuClx Stir (takes about 5 min) Add 5-10 drops of 10% HCl and stir ( HCl will dissolve excess Al) Decant the supernatant liquid Cu Flow Chart for Procedure waste

  18. Flow Chart for Procedure Cu Wash with distilled water to remove aluminum chloride Transfer Cu residue to a pre-heated and pre-weighed casserole waste Do not overheat to avoid oxidation heat Determine the mass of Cu waste

  19. Procedure Notes • Record all weights to 0.001g • Weigh 25 ml of CuClx solution, use exact density to calculate exact volume, then calculate the mass of CuClx • Do not use metal forceps or spatulas • Add Al foil until blue color is gone, allow excess foil to dissolve also • Allow container to cool before weighing • Speed up cooling by placing in front of hood sash raised 4-6” • The second beaker does not have to be 150 mL • A casserole will also work as an evaporating dish

  20. Hazards • 10% HCl-strong acid, corrosive • CuClx solution-heavy metal, irritant • Hot surfaces - hotplates, glassware Waste • Liquid Waste: Al+3 / HCl • Cu solids

  21. Summary of Data & Calculations Collected data Results (calculations) Mass percent of Cu Mass of Cl Mass percent of Cl Empirical formula Mass of CuClx Mass of Cu

  22. Next Week’s Experiment: Antacid Analysis (green book) Additional background reading for Antacid Analysis/Titrations: Atkins, “Chemical Principles”, 3rd ed, pp. F67-F72, F85-F88, 415-425

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