April 23, 2015 Lab 1 - Gravimetric Analysis of a Metal Carbonate

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1 Lab 1 - Gravimetric Analysis of a Metal Carbonate Purpose - to determine the identity of the cation in X 2 CO 3 by gravimetric analysis Lab Highlights Include: SLOW gravity filtration Primary Experimental Techniques/Issues/Errors: Solid not completely dry (mass to large, ratio of g/mol too large) Not all solid transferred to filter paper (mass to small, ratio of g/mol too small)

2 Lab 2 - Oxidation/Reduction Titration Purpose: To determine concentration of oxalic acid by redox titration Lab Highlights Include: Using a buret (this was notable then!) Standardizing a solution of potassium permanganate with iron(ii) solution - need to standardize in order to know the exact concentration of the permanganate Potassium permanganate is deep purple Primary Experimental Techniques/Issues/Errors Rinse buret with water, then 3x with titrant (avoid dilution by the water rinse) End point reached when purple color of permanganate does not disappear when added to test solution Use balanced equation (using half-titration method) to get ratio of permanganate to solution being tested Sulfuric acid is added to produce hydronium ion

3 Lab 3 - Hess' Law Purpose - To demonstrate that enthalpies of reaction "steps" can be summed to get total reaction enthalpy of a final reaction Lab Highlights Include Using calorimeter Get heat for each process using q=cm t, then divide by moles to get enthalpy (kj/mol) Primary Experimental Techniques/Issues/Errors Need to figure out the heat capacity of the calorimeter first, did this with hot water and recorded the temperature change over a short period of time

4 Lab 4 - Molar Mass of a Volatile Liquid Purpose - To determine the molar mass of a volatile liquid by filling the flask with the vapors of that liquid Small amount of liquid in the bottom of a large flask (dyed), aluminum foil with a pinhole placed on top Submerged into hot water to form a vapor of the liquid, allowed to cool, only the liquid that was required to fill the flask condensed within the flask Obtain mass of liquid by mass difference with empty flask Find moles by using ideal gas law and experimental conditions Primary Experimental Techniques/Issues/Errors Need volume of flask, obtain by filling with water and measuring volume (or mass if you have required equipment)

5 Lab 5 - Separation of a Dye Mixture by Chromatography Purpose - To develop a procedure to determine the dyes that make up a mixture Inquiry-Based, meaning you were responsible to solve the problem using your own procedure rather than follow a "cookbook" procedure and then spit out an answer Used polarity differences of solvents to optimize separation (resolution greater than 1) between each of the 2 or more dyes in the mixture Test substances will "cling" to the mobile phase more if it has a similar polarity, result in greater motion across the chromatography paper Primary Experimental Techniques/Issues/Errors: Best strategic starting point - run your test solution using the SAME mobile phase as the initial standard, compare to narrow down what standards are possibly present. Then adjust with higher/lower polarity as needed in order to maximize resolution and identify each of the standards

6 Lab 6 - Rate of Crystal Violet Fading Purpose - To determine the pseudo-rate law for the decomposition of crystal violet with hydroxide using UV/Vis spectroscopy. Used Spec-20 with wavelength set to visible range where maximum absorbance occurs Established a calibration curve first with known concentrations in order to relate absorbance to concentration Recorded transmittance (first) or absorbance data at regular intervals after the reaction was initiated in order to get concentrations and plot A = 2 - log (%T), A = abc Natural log of concentration provided linear plot, was first order decomposition Crystal violet is purple (duh!)

7 Lab 7 - Preparation of Esters Purpose - To prepare 3 esters, identify by scent, and name correctly Esters are highly aromatic Name the functional group on each side of the ester group (ethyl acetate, for example, has an ethyl group and an acetate group separated by the ester group)

8 Lab 8 - Separation & Qualitative Identification of Cations/Anions Purpose - To determine the cations and anions that make up two unknown mixtures Lab Highlights Lots of centrifuging! Prepared precipitates from several ions, then re-dissolved (didn't know it at the time, but you redissolved by preparing complex ions) Performed tests with standard solutions, then unknown solutions to compare > Silver ion - ppt with chloride, redissolved with excess chloride > Copper(II) ion - ammonia turned it deep blue > Iron (III) ion - ppt in hydroxide, redissolved in acid, formed FeSCN 2+ with KSCN (deep red) > Zinc ion - complexes with iron hexacyanate ion to produce a ppt > Chloride - ppt with silver ion, redissolved with excess ammonia > Carbonate - acid produced effervescence, bubbled the gas into barium hydroxide - produced white ppt of barium carbonate > Sulfate - added barium chloride, formed white ppt > Nitrate - oxidizes solid aluminum

9 Lab 9 - Determination of K(eq) of FeSCN 2+ Purpose - To determine the equilibrium constant for the following reaction: Fe 3+ + SCN - FeSCN 2+ yellow colorless deep (blood) red Used Spec-20's again! You knew initial concentration of each of the reactant ions when you prepared the solutions. You used absorption data to determine the product concentration, then you used that concentration to determine K(eq)

10 Lab 10 - Applications of LeChatelier's Principle Purpose - To draw conclusions about the direction of shifts in equilibrium based on stresses six systems tested with various stresses, including pressure, heat, concentration changes

11 Lab 11 - Hydrolysis Purpose: To determine the ph of ionic salt solutions not typically considered to be acids or bases Used ph paper to get a rough idea about the ph of numerous 0.1M solutions, then categorized each as acidic, basic, or neutral Conjugate acids of strong bases (alkali metal ions) or conjugate bases of strong acids (most halides, nitrate, sulfate) did not effect ph Conjugate bases of weak acids (acetate, bicarbonate for example) accept protons from water, leave basic solutions Conjugate acids of weak bases (ammonium, aluminum for example) donate protons to water (or in metal ions' case, with no proton to donate, result in proton donation by binding to the hydroxide group in water)

12 Lab 12 - Determine K(a) of Weak Acid Purpose - To determine the K(a) of an unknown weak acid Second method used in order to determine an equilibrium constant Performed "half-titration" (at the time you didn't fully understand this term) where you dissolved your acid, then divided it in half. You added sufficient base to turn phenolphthalein just pink, then you combined it with the unreacted portion and measured ph. Remember that the half-titration is incredibly helpful at this point because when we substitute into the formula: [H + ]=K(a)[HA]/[A - ] a value for both HA and A - that are EQUAL, which occurs at the halftitration, then hydronium ion concentration is the same as K(a).

13 Lab 13 - Properties of Buffer Solutions Purpose: To produce and test a buffer exposed to various stresses Buffer solutions are used in numerous commercial applications. Given a small amount of information, you were to prepare a buffer that compares to some of these and then test it with acid and base stressors Depending on the buffer, not all worked with the greatest amount of stress, but when stressed within the reasonable boundaries of the buffer, ph change was minimized

14 Lab 14 - Acid/Base Titration Purpose - To titrate an unknown acid and plot the curve Became experts with burets! Applied all the acid/base theory we have to this experiment (produced a buffer in the early portion, identified the end point and the equivalence point where conjugate base only was present, continued to add excess hydroxide until the curve flattened again)

15 Lab 15 - Activity Series Purpose - To develop a table of elements in order of ease of reduction Single displacement reactions performed between metals and metal ions, some worked and others did not Also performed between halogens and halides to produce a table for halogens as well Primary Experimental Techniques/Issues/Errors Oxide coatings can interfere Some metals look similar and have similar potentials, make for subtle/ difficult confirmations (Mg & Zn for example) Halogens are easily identified when they are extracted into nonpolar oil (chlorine = green, bromine = orange, iodine = purple) Chlorine + Sodium Bromide - what would we see before and after in the oil?

16 Lab 16 - Voltaic Cells Purpose - To measure the cell potential of voltaic cells prepared with both standard and non-standard concentrations Identify anode and cathode - anode has the more negative reduction potential, flip the reaction and sign, and add to the reduction potential of the cathode to get literature value For non-standard cells and concentration cells, Nernst equation was needed Salt bridge is required to be in contact with both half-cells in order for the cell to produce electricity Any oxide coating on the surface of the metal can cause an error in measurements

EXPERIMENTS. Testing products of combustion: Reducing Copper(III) Oxide to Copper. Page 4

EXPERIMENTS. Testing products of combustion: Reducing Copper(III) Oxide to Copper. Page 4 APPARATUS Page 2 APPARATUS Page 3 Reducing Copper(III) Oxide to Copper EXPERIMENTS Page 4 Testing products of combustion: EXPERIMENTS Showing that oxygen and water is needed for rusting iron Page 5 Showing