Download CHEM 2545 Midterm/Final Exam Prep Questions and Answers and more Exams Organic Chemistry in PDF only on Docsity!
CHEM 2545 MIDTERM/FINAL EXAM 2025/
ACTUAL PREP QUESTIONS AND ANSWERS GRADED
A+
How do you know an acid is contaminated from the bottle?
contaminated acids are not clear
What are the two things to do if you get an acid or base on your skin
immwsiately flush the area of your skin with water for 10 min and tell your TA.
Why is acetone a usefull solvent?
it dissolves many compounds with low water solubility
What does each household object stand for in lab 1 (eggs, sugar, aluminum foil, and styrofoam)
- egg: protein in our skin
- sugar: major component in our skin
- aluminum foil: metal jewlery
- styrofoam: contact lenses
Prior to begining an experiment what should be in your lab notebook?
- title
- objective
- overall reaction
- table of reagents
- experimental set up
- procedures
Before you leave the classroom it is important to remove what?
Gloves
Extensive properties
dependent on the amount of sample used
Intensive properties
- dependent upon the identity of the component in the sample.
- as the solution cools the solid crystalizes slowly and pure crystals form excluding impurities.
tips for a good recrystallization
- Watch your sample
- add the perfect amount of solvent
- heat and stirr
refractive index
- defined as (n)
- can be used to identify a liquid or asses the purty of a sample by comparing the observed n to reference values.
n= (velocity of light in air)/(velocity of light in liquid)
Mixed melting point
10% of a known compound is added to an unknown sample. If the melting point of the unknown solid by itself matches the mixed melting point, there is strong support that the unknown solid and the known solid are the same.
Strongest to weakest intermolecular forces
hydrogen bonding, dipole-dipole interactions, London dispersion forces
oiling out
a condition where the solid melts in the recrystallization solvent but does not dissolve.
percent weight recovery
(mass of recrystallized compound)/(mass of impure compound) x 100
What does TLC test for?
- the completeness of a reaction
- purity of a compound
- identification of a product when compared to standard sample
- separates mixtures of compounds
What is stationary phase and what are the most common layers?
- a solid support layered on a plastic, aluminum, or glass sheet/plate.
- common ones are silica gel (polar) or alumina (non polar)
- the difference between electronegativity.
- asymmetry in molecular structure.
Retention Factor
a ratio used to characterize and compare components of samples in liquid chromatography
(distance compound travels)-A/(distance solvent travels)-B
When looking at a TLC plate how do you know that it is polar or non polar
The solvents most polar do not move much up the TLC plate, but non polar ones move all the way up.
When showing hydrogen bonding and silica TLC plate where must the bonds go towards
The bonds goes towards the acceptors lone pair
Lewis acids and bases do what to electrons?
lewis acid: accepts
lewis base: donates
Bronsted acids and bases do what to protons?
acid: donates
base: accepts
When pka increases, what happens to the acidity?
The higher the pka the weaker the acid and the lower the pH
Organic acids only react with what?
Organic bases only react with what?
- bases and then they lose a proton.
- acids and then they gain a proton.
When two solids mix together they are seperated into what layers?
- ether layer
- aqueous layer (has charges)(conjugate acid)
constitutional isomers
same molecular formula, different connectivity
reflux
- a method for adding energy to a. reaction.
- recycles solvent
- cool water causes the vaporized solvent to return to liquid phase.
What is the source of Bromine?
- dihalides will add across an alkene or alkyne
During the reflux, why do you place the reaction flask in water and not sand.
- water has a lower boiling point than acetic acid
Nucleophiles
- an electron rich species that can donate a pair of electrons to form a bond.
- strong nucleophiles are more willing to donate electrons
- EX) halides, hydroxyl, sulfide, amide, alloys, water, alcohols, amines
electrophiles
- a species that can accept an electron pair from the nucleophile to form a bond.
leaving groups
good LGs:
- resonance stabilized
- weak bases
- neutrals (start with positive charge)
bad LGs:
- strong bases
- but protonating them can make them good
ugly LGs:
- hydrogens
- alkanes
SN2 reaction
-bimolecular nucleophilic substitution reactions
- only 1 step (concerted reaction)
-nucleophile attacks the compound at the same time as the leaving group leaves
product determination
- After the first reflux period, the top layer is 1-bromobutane.•
- In the first wash, 1-bromobutane is in the bottomlayer.• - After the second and third wash, 1-bromobutane isin the bottom layer.
beilstein test
- place the copper wire in the flame for a few seconds to burn off any remaining residues from the person before you.
- if the flame os green this suggests the product is 1-bromobutane
What is a thin colorless layer that is formed on top of a reaction mixture?
- organic solvent layer and this is formed when something that is less dense than water is in an aqueous mixture.
Would you expect 1-butanol or 1-bromobutane to have a lower boiling point? Describe the intermolecular forces present in each to justify your answer and indicate which of these forces are stronger
- 1-bromobutane would have a lower boiling point due to its dipole-dipole interactions. These interactions are one of the stronger intermolecular interaction and 1-butanol has a stronger H-bonding interaction.
SN1 reaction
- unimolecular nucleophilic substitution reaction
- multistep
- nucleophile is substituted for a leaving group
how do leaving groups affect sn
- Atom or group that leaves during a substitution or elimination reaction
- Must be electron withdrawing
- Creates a partial positive charge on the carbon atom• - Should be polarizable
- Maintains partial bonding to the carbon atom in therate limiting transition state
- must be stable once it has left reactant.
- can be charged or uncharged
how does carbocation stability and alkyl halide structure affect sn1?
- since sn1 goes through a carbocation intermediate, the more stable a carbocation, is the faster it will form.
- more substituted are more stable
- alkyl groups donate electron density to stablize a carbocation
Before you leave the classroom it is important to remove what?
Gloves
How do you know an acid is contaminated from the bottle?
contaminated acids are not clear
What are the two things to do if you get an acid or base on your skin
immwsiately flush the area of your skin with water for 10 min and tell your TA.
Why is acetone a usefull solvent?
it dissolves many compounds with low water solubility
What does each household object stand for in lab 1 (eggs, sugar, aluminum foil, and styrofoam)
- egg: protein in our skin
- sugar: major component in our skin
- aluminum foil: metal jewlery
- styrofoam: contact lenses
Extensive properties
dependent on the amount of sample used
Intensive properties
- dependent upon the identity of the component in the sample.
- color
- melting point
- boiling point
- density
- refractive index
- solubility
- molecular weight
The _____ the intermolecular forces, the ____ the energy to overcome them and the ____ the boiling and melting point
n= (velocity of light in air)/(velocity of light in liquid)
Mixed melting point
10% of a known compound is added to an unknown sample. If the melting point of the unknown solid by itself matches the mixed melting point, there is strong support that the unknown solid and the known solid are the same.
Strongest to weakest intermolecular forces
hydrogen bonding, dipole-dipole interactions, London dispersion forces
oiling out
a condition where the solid melts in the recrystallization solvent but does not dissolve.
percent weight recovery
(mass of recrystallized compound)/(mass of impure compound) x 100
What does TLC test for?
- the completeness of a reaction
- purity of a compound
- identification of a product when compared to standard sample
- separates mixtures of compounds
What is stationary phase and what are the most common layers?
- a solid support layered on a plastic, aluminum, or glass sheet/plate.
- common ones are silica gel (polar) or alumina (non polar)
What interactions can silica gel take place in?
- hydrogen bonding
- dipole-dipole
What is a mobile phase?
Liquid that moves past the surface of the silica gel
- only compound not bound to the surface of the silica gel
What type of compounds move up a TLC plate rapidly?
- compounds with a high affinity for the mobile phase or no affinity for the stationary phase will move rapid.
