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Chem 120L

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Sue Stathopulos

Experiment 1 & 2 Experiment #1: The Chemistry of Copper Compounds  Synthesis of Copper compounds form metallic compounds o Cu  Cu(NO ) 3 2(OH)  CuO 2 CuSO 4 5H 2  Cu  Synthesis of Copper (II) Nitrate and Copper (II) Hydroxide o Cu (s)+ 4NO 3(aq) Cu(NO )3 2(aq)+ 2NO 2(g)2H O2 (l) o Cu(NO ) 3 2(aq) 2NaOH (aq) Cu(OH) 2(s)+ 2NaNO 3(aq)  Synthesis of Copper (II) Oxide o Cu(OH) 2(aq) CuO (s)+ H 2 (l)  Synthesis of Copper (II) Sulphate o CuO (s)+ H 2O 4(aq) CuSO 4(aq) H 2 (l)  Recovery of Copper o CuSO 4(aq) Zn (s) Cu (s)+ ZnSO 4(aq) o Zn (s)+ 2HCl (aq) ZnCl 2(aq)+ H 2(g)  Percent Recovery o ( Initial Mass / Recovered Mass ) x 100%  Common Errors: o Bumping: superheating causing overflowing of liquid due to bubbles forming rapidly o Weighing the final sample of recovered copper when it is still wet, giving a higher mass and a larger percent o The overheating of Copper or the loss of copper in the decanting the supernatant  Experimental Procedure o Part 1: Synthesis of Copper (II) Nitrate and Copper (II) Hydroxide  Obtain an length of copper wire and a piece of sandpaper, sand wire and weigh on analytical balance  Place copper wire in beaker in fume hood with 10 mL of Nitric Acid, let wire dissolve, bright blue solution  Dilute with 25mL of deionized water, stir in 25mL of 20% NaOH o Part 2: Synthesis of Copper (II) Oxide  Heat the mixture and stir to prevent bumping until boiling point is reached, then heat for one more minute or until completely black, add more NaOH(20mL) until black  Isolate with solid CuO with vacuum filtration, using Buchner funnel to quantitively transfer CuO  Use three 10mL portions of deionized water to rinse out the beaker into the funnel  Wash the CuO with water to replace the NaNO and 3 NaOH with water. Collect all CuO on filtrate paper o Part 3: Synthesis of copper (II) Sulphate  Convert CuO to CuSO with dilute sulphuric acid 4  CuO is water soluble and dissolves releasing Cu 2+ ions 2+ that are hydrated to form Cu(H O) 2 4 . Due to high solubility the copper sulphate will not be isolated to produce Cu  Transfer CuO back into original beaker from filtrate paper and wash the paper with 20mL of 3M H SO use2 4 10mL of deionized water to wash out the acid  If the black CuO doesn’t dissolve completely, boil gently until it is dissolved giving a blue solution, use 5mL water to rinse adhering solution out after transferring supernatant liquid to a 100mL beaker o Part 4: Recovery of Copper  Zinc is more chemically active than copper and displaces copper (II) ions from solution, and settles quickly. The excess zinc is removed with HCl. When H gas bubbles stop, Zn is completely dissoluted  2g of zinc was weighed using the top loading balance and was added in small portions to the blue Copper (II) sulphate solution. The solution was stirred until the blue colour disappeared (copper(II) sulphate converted to copper and Zinc Sulphate) The solid is Zn and Cu metal  Add 10mL of 6M HCl in the fume hood to dissolve the Zn  When the reaction of Zn and HCl has stopped the copper was allowed to settle and the supernatant was decanted. The solid was washed with two separate 50mL portions of water. Decant after washing  Using the analytical balance, weigh a clean and dry evaporating dish. Transfer the Cu to the evaporating dish using as little water as possible to wash it out. Warm the dish until the water is evaporated but do not burn off the Cu. Allow to cool, and weigh again. Experiment #2: Acid-Base Titrations: The Identification of an Unknown Solid Acid  Strong and Weak Acids o Strong acids are fully ionized in aqueous solution, weak acids are only partially ionized o Analogous situation arises when a strong acid and a weak base are mixed Strongest Perchloric acid HClO 4 ClO4- Perchlorate Weakest ion - Nitric acid HNO 3 NO 3 Nitrate ion Hydrochloric acid HCl Cl Chloride ion Sulphuric acid H2SO 4 HSO 4- Hydrogen sulphate ion + Hydronium ion H3O H2O Water Acid Phosphoric acid H3PO 4 H2PO 4- Dihydrogen Acid Strength phosphate Strength ion Acetic acid CH 3OOH CH COO3 - Acetate ion Carbonic acid H2CO 3 HCO 3- Hydrogen carbonate Dihydrogen H PO - HPO 2- Hydrogen 2 4 4 phosphate ion Phosphate Weakest Strongest ion + Ammonium ion NH 4 NH 3 Ammonia Hydrogen HCN -CN Cyanide ion cyanide _ 2- Hydrogen HCO 3 CO 3 Carbonate carbonate ion ion Methylammoniun CH NH 3 3+ CH3NH 2 Methylamine ion Water H2O -OH Hydroxide ion methane CH -CH Methide ion 4 3  Acid Base Reactions o o This reactions goes to completion whether HA is a strong acid or a weak acid  Strong Acid – Strong Base Reactions o o Both HCl and NaOH are strong and will be fully ionized in aqueous solution o The reaction can be simplified to:   Weak Acid – Strong Base Reactions o Weak Acid – Weak Base Reaction  o Strong Acid – Strong Base  o Overall Reaction   Weak Acid – Strong Base Titrations o Titration: use a solution of known concentration to establish the concentration of a second solution o Equivalence point is reached when no excess reactant remains  Monoprotic acids o One acidic H  Diprotic acids o Two acidic Hs  Triprotic acids o Three acidic Hs  Primary Standard o The accuracy of a volumetric analysis is critically dependent on the primary standard since all successive calculations are based on its accuracy o A primary standard solid must be obtained easily in 100.0% purity, weighed and diluted with great accuracy because error will affect the accuracy of the entire analysis o The amount of acidic Hs per mole of acid will neutralize that many moles of OH- ions  Calculations Experiment 3: Dumas Method for Determining the Molar Mass of a Volatile Liquid BE ABLE TO MANIPULATE THE GAS LAWS Ideal Gas Law: PV = nRT Finding Moles: n = m/M Rearranging the 2 Equations: M = mRT/PV KNOW WHAT ASSUMPTIONS ARE MADE ALLOWING US TO USE THIS METHOD, AND UNDERSTAND THE THEORY BEHIND THIS METHOD  the molar mass of a volatile (easily vaporized) liquid can be determined using a method originally developed by John Dumas in 1826  when molar mass is determined, it can be compared to known molar masses in order to identify the volatile liquid used  accuracy of this method depends on ability of the volatile liquid vapours to behave as an ideal gas  there should be less error in determining the molar mass of a liquid with weak intermolecular forces compared to one with strong intermolecular forces  method involves placing a volatile liquid into an Erlenmeyer flask and covering the opening with aluminum foil, a small hole is made in the foil to allow excess vapour to escape  when heated in a boiling water bath, the volatile liquid vaporizes, first driving out any air in the flask, then continuing to push out all excess vapour, until the pressure inside the flask equals the atmospheric pressure outside the flask  the temperature of the water bath will be equal to the temperature inside the flask, the volume occupied by the vapour is equal to the interior volume of the flask, after cooling the mass of the condensed vapour can be found and from these values it is possible to calculate the molar mass of the volatile liquid BE ABLE TO CALCULATE MOLAR MASS M = = = 13.08 g/mol BE ABLE TO CALCULARE PERCENT ERROR % error = x 100% = x 100% = 20.98% KNOW COMMON ERRORS, AND EFFECTS THEY HAVE ON THE RESULTS  boiling water too vigorously may result in losing your water bath to evaporation  ensure no water gets inside the flask: you will need to start the experiment over Experiment 4: Enthalpy of Neutralization KNOW THE EQUATIONS OF THE REACTIONS INVOLVED The neutralization reaction between HCl and NaOH: H + Cl + Na + OH  HOH + Na + Cl + - Eliminating what is common to both sides gives: H + OH  HOH Neutralization of acetic acid with sodium hydroxide will occur in two steps: 1. CH 3OOH  CH COO3+ H - + + - 2. H + OH  HOH BE FAMILIAR WITH THE TERMINOLOGY: SPECIFIC HEAT, HEAT CAPACITY, ENTHALPY, ETC. Specific Heat (s): the heat necessary to raise the temperature of one gram of a substance by one degree Heat of Reaction (q): the heat absorbed or released during a complete chemical reaction Heat Capacity: the product, specific heat x mass Enthalpy: KNOW HOW TO CALCULATE Q, ∆H, MOLES OF WATER FORMED, ETC ∆H (joules) = q = specific heat (joules/deg g) x mass (g) x ∆T (deg) * know calculations, look at lab for moles of water, number of kJs/mol water, etc* KNOW HOW TO FIND ∆T, THE TEMPERATURE CHANGE ∆T = final temp – initial temp KNOW WHAT ASSUMPTIONS ARE MADE ALLOWING US TO USE THIS METHOD, AND UNDERSTAND THE THEORY BEHIND THIS METHOD  calorimetry is the science of measuri
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