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CHEM 2545 Midterm/Final Exam Prep Questions and Answers, Exams of Organic Chemistry

A comprehensive set of questions and answers covering various topics in chemistry, including intermolecular forces, recrystallization, tlc, and sn1/sn2 reactions. it's a valuable resource for students preparing for exams, offering detailed explanations and examples to aid understanding of key concepts. The questions are designed to test comprehension and application of theoretical knowledge.

Typology: Exams

2024/2025

Available from 04/22/2025

LennieDavis
LennieDavis 🇺🇸

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CHEM 2545 MIDTERM/FINAL EXAM 2025/2026
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
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pfd
pfe
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Partial preview of the text

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

  • mass
  • volume

Intensive properties

  • dependent upon the identity of the component in the sample.
  1. 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:

  1. resonance stabilized
  2. weak bases
  3. neutrals (start with positive charge)

bad LGs:

  1. strong bases
  2. but protonating them can make them good

ugly LGs:

  1. hydrogens
  2. 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

  • mass
  • volume

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

  • stronger
  • greater
  • higher

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.