What is the kinetic energy of an ejected electron equal to?
The difference between the photon energy and the ionization energy (binding energy).
What does a gaseous atom do to start photoelectron spectroscopy?
Absorbs a high energy UV or X-ray photon of electromagnetic radiation.
What does orbital ionization energy represent for an atom’s electrons?
The tightness of the attraction of an electron by the electrostatic attraction between positive protons in the nucleus and the negative charge of the electron.
If ionization energy was very high, what could be inferred of the released electron?
That the electron was very tightly bound.
Equation for ionization energy
|Ionization energy = E(photon) – E (KE)|
Hypothetically, if an electron was in a vacuum, then it’s energy level would be 0. This would be because there is no kinetic energy, and therefore no movement.
What is an electrostatic analyzer?
A tool used to measure the kinetic energy of a photoelectron. This is done by measuring the speed of the electrons
Why are the walls of an analyzer curved?
At the end of the “tunnel” there is a slit through which the electrons must move. Only electrons which move at a certain speed may pass through this aperture. Electrons which are too fast or too slow will collide with the walls of the curved analyzer and stick to the charged walls.
Why do the charges on the plates at the end of the curved analyzer change slowly?
They are used to scan the photoelectric spectrum by changing the amount fo positive and negative charges ont eh plates of the analyzer. This gradated change brings differently charged electrons into focus.
What is the photoelectron spectrum of a gaseous atom?
A set of peaks representing the energies of the orbitals.
Relationship between height of peak on graph and number of electrons.
Common reasons why one ionization potential is higher than the other:
-A has more protons and than B, therefore, the binding energy is greater
– its shell is half filled/all filled, and thus has great stability and resists losing electrons
– electron repulsions on outer-shell electrons beat the repulsions on degenerate orbitals
What do the wave functions include?
-a series of numbers called quantum numbers which are used to identify the different orbitals as to their average distance from the nucleus.
Z(eff) = Z (actual) – (electron repulsions)
Why are the 4s orbitals normally chosen over the 3d orbitals in choosing electrons for the creation of ions?
4s orbitals, although filled before the 3d orbitals, are nonetheless at a higher energy level, and the atom can’t wait to get rid of their electrons
What is the active compound in aspirin?
What can be done to make salicylic acid less irritating to membranes?
Replacement of the acidic OH group with an acetyl group
What group do esters contain?
Characteristics of an ester (o-hydroxybenzoic acid, in this case)
Acetylsalicylic acid : white, powdery like talc
Methyl salicylate : Pleasant smell
What would be observed after placing a drop of 1% iron III chloride into a test tube containing salicylic acid?
The solution would turn hot pink or purple.
Reactants of acetylsalicylic acid:
Salicylic acid + acetic anhydride è Aspirin + Acetic Acid
Normally, it is made from salicylic acid and acetic acid, but this lab uses a more reactive compound called acetic anhydride. (add an acetyl O=<H3C + O group)
Reactants of methyl salicylate:
Salicylic acid + methanol, add CH2 to the right-hand OH, KEEP the hydroxyl group on top.
A class of compounds where OH is attached to a benzene ring. Present in salicylic acid and methyl salicylate, but not aspirin. This stuff can kill you. Colors: green/blue, red/purple in presence of 1% iron III ion
Procedure for synthesis of aspirin (6 steps)
1) measure 2.8 to 3.2 g salicylic acid and transfer to 125 ml flask
2) add 6 ml acetic anhydride and five drops of sulfuric acid.
3) mix thoroughly and place flask in boiling water (80 degrees Celsius) for 20 minutes
4) place in an ice-water bath and add 40 ml of DI water and wait for crystals to form, breaking up any oil that collects at the top
5) filter the product. Use the air-filter tap on the sink. Press dry. Air dry crystals.
6) weigh and conduct the 1% iron III Cl test. Does it turn purple? If so, there is unreacted salicylic acid present.
What is recrystallization?
Dissolving a substance in a suitable solvent at the solvent’s boiling point allowing them to recrystallize and leave impurities behind in the solution.
What is characteristic of a good solvent?
High temp=high solubility, low temp=low solubility
During recrystallization, how much ethanol is needed to dissolve the crude product?
10ml for every 3 grams. (cross-multiply)
(grams salicylic acid used) x (1 mol salicylic acid)/(grams salicylic acid in 1 mol) = mols salicylic acid
mols salicylic acid = mols of expected product of aspirin
crude product/ expected product
dry product / expected product
Carboxylic acid group
Reaction where wet aspirin decomposes into a benzene ring with a carboxylic acid group and a phenol group attached, as well as a mol of acetic acid
Phenolphthalein in the presence of bases
Purpose of back-titration
To determine the moles of pure aspirin by backtitrating the NaOH with HCl.
The moles of hydroxide consumed are equal to…
… the mols of acetylsalicylic acid in the product
What is the point of doing an initial titration?
To determine the total number of moles of acid species in the product
A reaction where heat is used to drive the decomposition of aspirin with NaOH
What do we use the ethanol for?
To neutralize the acids in the solution
Moles of hydroxide [OH-] equal ….
… moles of acetylsalicylic acid.