C127 Final Exam Information 4-27-16 ∙ 6 experiments:
o Milk separation
o Calcium in Milk & OJ
o Bioanalytical spectroscopy
∙ 120 pts; will try to have around 20 per experiment
∙ Format will be same as midterm exam
o Aspirin- If a compound is pure, expect to see single spot above where you put the compound on the TLC plate
▪ More than 1 spot indicates more than 1 distinctly different mixed compounds
▪ Compound smearing up the plate indicates impurity
If you want to learn more check out What is the meaning of personalized?
o Kinetics- Reactant in excess:
▪ 0.010 M solution of iodine is reacted with large excess of 2-butene and [��2], ln[��2], and 1[��2]were plotted vs. time Don't forget about the age old question of Adult to adult liver transplants began in the u.s. in what year?
▪ ln[��2] is linear; first-order with respect to iodine
▪ Consider [2-butene] to be constant
▪ When concentration of 2-butene doubles, rate of reaction doubles
∙ First-order with respect to 2-butene We also discuss several other topics like Who is herbert hoover?
▪ Overall second order
▪ �������� = ��[��2][2-butene]
We also discuss several other topics like What happens to the market for gas when the price of steel falls?
o Milk- Adding acid and heating in separation 1:
▪ Heating increases temperature, increases rate of reaction
▪ Reaction was acid/base- casein acted as base, added acetic acid
∙ Casein has some negatively charged polar side groups, some nonpolar; twists and folds so polar ones end up on surface (like soap molecule)
∙ Acid (containing ��+) reacting with side groups makes casein neutral, no longer hydrophilic; rotates so protonated groups go inside, whole molecule becomes less hydrophilic
▪ Molecules start to clump together and energy of collision with water not enough to stay in suspension as precipitate Don't forget about the age old question of What is dipole induced dipole?
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o Milk- Denaturing proteins (heating whey):
▪ Whey protein much smaller than casein
▪ Enough energy put in to break intermolecular forces and unravel protein
▪ Unwinds like a spring; as heat removed, protein comes back together in random shape such that it cannot stay in suspension
o Bioanalytical Spectroscopy:
▪ Learning goals:
∙ Learn principles of UV-Visible absorption spectroscopy
∙ Learn how absorption of light is related to concentration (Beer’s Law)
∙ Use spectroscopy to determine concentration of whey protein in milk
▪ Ex. 3 students made a phosphate solution from a 0.0200 M stock solution. Rose and Emily took diluted 1.0 mL of the solution to 10.0 mL. Daniel took 2.0 mL of the solution and diluted it to 10.0 mL. Rose and Daniel both measured the absorbance of their solution using a 1 cm cell, while Emily used a 2 cm cell. They used the same spectrophotometer and measured their solutions at the same wavelength. Whose solution would have the highest absorbance reading?
A. Rose B. Daniel C. Emily D. Rose and Emily E. Daniel and Emily F. All would be the same
∙ Daniel’s solution most concentrated
∙ All have same absorptivity (all measured at same wavelength, �� changes with wavelength) ∙ Different path lengths; Emily used longest path length
∙ �� = ������ where �� = absorptivity, �� = path length, �� = concentration
o Double path length = double absorbance
o Double concentration = double absorbance
o ∴ Daniel and Emily (both will be twice Rose’s)
▪ Several steps to get to concentration from absorbance:
∙ Have a standard solution with known molarity
∙ Make other known concentrations using first solution (dilution)
o ��1��1 = ��2��2
∙ Measure absorbances
∙ Plot �� vs. �� (�� vs. ��)and find relationship between absorbance and known concentration (calibration graph)
o Should have intercept at (0, 0) → get equation �� = ���� or �� = (����)��
∙ Using equation, calculate concentration of experimental samples from measured absorbance
▪ Questions could be anything related to this process
o Calcium in Milk/OJ- Titration:
▪ Learning Goals:
∙ Use a titration to determine quantity of a species in aqueous solution
∙ Properly use/read a buret
∙ Understand parts per million (ppm) as unit of concentration
▪ Ex. An EDTA solution is standardized by titrating 4 samples of a calcium solution with the EDTA. The following concentrations were obtained: 0.0101 M, 0.0108 M, 0.0102 M, and 0.0102 M, and the standard deviation of the measurements is 0.003. The average value should be reported as ________ because the value 0.0108 should be excluded/included.