April 23, 2015
Lab 1 - Gravimetric Analysis of a Metal Carbonate
Purpose - to determine the identity of the cation in X2CO3 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)
April 23, 2015
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
April 23, 2015
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
April 23, 2015
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
Lab Highlights:
• 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)
April 23, 2015
Lab 5 - Separation of a Dye Mixture by Chromatography
Purpose - To develop a procedure to determine the dyes that make up a mixture
Lab Highlights:
• 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
April 23, 2015
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.
Lab Highlights:
• 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!)
April 23, 2015
Lab 7 - Preparation of Esters
Purpose - To prepare 3 esters, identify by scent, and name correctly
Lab Highlights:
• 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)
April 23, 2015
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 FeSCN2+ 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
April 23, 2015
Lab 9 - Determination of K(eq) of FeSCN2+
Purpose - To determine the equilibrium constant for the following reaction:
Fe3+
yellow
+ SCNcolorless
FeSCN2+
deep (blood) red
Lab Highlights:
• 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)
April 23, 2015
Lab 10 - Applications of LeChatelier's Principle
Purpose - To draw conclusions about the direction of shifts in equilibrium based
on stresses
Lab Highlights:
• six systems tested with various stresses, including pressure, heat,
concentration changes
April 23, 2015
Lab 11 - Hydrolysis
Purpose: To determine the pH of ionic salt solutions not typically considered to
be acids or bases
Lab Highlights:
• 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)
April 23, 2015
Lab 12 - Determine K(a) of Weak Acid
Purpose - To determine the K(a) of an unknown weak acid
Lab Highlights:
• 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).
April 23, 2015
Lab 13 - Properties of Buffer Solutions
Purpose: To produce and test a buffer exposed to various stresses
Lab Highlights:
• 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
April 23, 2015
Lab 14 - Acid/Base Titration
Purpose - To titrate an unknown acid and plot the curve
Lab Highlights:
• 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)
April 23, 2015
Lab 15 - Activity Series
Purpose - To develop a table of elements in order of ease of reduction
Lab Highlights:
• 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?
April 23, 2015
Lab 16 - Voltaic Cells
Purpose - To measure the cell potential of voltaic cells prepared with both
standard and non-standard concentrations
Lab Highlights:
• 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