Orgo 1 Lab Exam 2

How should a melting point be reported?

As a range: the temperature from the first sign of melting to the point of being completely

liquid (e.g.

120-122°C).

What is the formula for percent recovery?

(Recovered amount ÷ initial amount) × 100

Can percent recovery exceed 100%

Yes due to impurities solvent residue or measurement error.

Why is thermometer placement important in distillation?

The bulb must be at the vapor path to ensure accurate boiling point measurement.

What are the primary safety concerns during distillation?

Never seal the system

What is reflux?

Heating while condensing vapors back into the flask allowing a reaction to occur at

boiling temperature without losing solvent.

Why perform reflux?

Speeds up reactions while preventing loss of volatile components

What is NMR spectroscopy used for

Determines molecular structure

What is the primary use of Thin Layer Chromatography (TLC)?

Quick qualitative analysis

What is the primary use of Column Chromatography?

Purification

When is Short Path Distillation used

For small amounts of compounds with high boiling points

How does steam distillation differ from other methods?

It uses water and an immiscible compound to lower the boiling temperature

When is steam distillation preferred?

For heat-sensitive

high boiling compounds

What are the basics of separation theory?

It is based on differences in boiling point

polarity

How is the total vapor pressure calculated in immiscible systems?

Total vapor pressure equals the sum of individual vapor pressures

resulting in a lower

boiling point

What are the common IR absorption peaks for essential oils?

Often C=C (~1600 cm⁻¹) and C-H (~3000 cm⁻¹)

Solvents & layer arrangement in extraction

Organic (less dense) = top; aqueous (more dense) = bottom (depends on solvent density)

SN2 mechanism basics

One-step

backside attack

Nucleophile and electrophile

Nucleophile = alkoxide; Electrophile = alkyl halide

Why brine wash?

Removes water from organic layer

Solid produced during synthesis

Salt (e.g.

NaBr)

What is the primary advantage of short path distillation compared to other methods?

The shorter distance the vapor travels results in less product loss.

Why is an ice bath used when handling diethyl ether?

Diethyl ether is very volatile due to its low boiling point.

What determines the chemical shift of a signal in NMR?

The electron density around the nucleus

where deshielding shifts the signal downfield.

What is the splitting pattern rule?

n+1 rule

What is the function of a beaker?

mixing

What is the function of an Erlenmeyer flask?

swirling

What is the function of a round-bottom flask?

reactions/distillation

What is the function of a graduated cylinder?

measure volume

What is the function of a pipette?

transfer liquids

What is the function of a condenser?

cool vapors

What is the function of a thermometer?

temperature measurement

Key lab safety guidelines

Wear goggles

gloves

hood when needed; know location of safety equipment (eyewash

shower

extinguisher)

Proper chemical waste disposal

Organic waste → designated containers; aqueous waste → separate container; solids →

solid waste; never pour unknowns down drain; follow lab-specific instructions

Proper lab notebook techniques

Write in pen

no erasing

observations clearly

cross out mistakes (don't erase)

What are the safety precautions for using a MelTemp apparatus?

Don't touch hot apparatus

use capillary tubes carefully

cooling before reuse.

What are the characteristics of an ideal melting point?

A narrow range (1-2°C) that is close to the literature value

which indicates high purity.

What is the effect of impurities on a substance's melting point?

Impurities lower the melting point and broaden the melting range.

How do you assess purity using melting point data?

A melting point that is close to the literature value and has a narrow range indicates a

pure substance; a lower and broader range indicates an impure substance.

What is the difference between extraction and washing?

Extraction removes the desired compound

while washing removes impurities

What is IR spectroscopy used for?

Identifies functional groups

How does IR spectroscopy affect molecules?

It measures bond vibrations via the absorption of IR radiation

What does NMR do?

Detects environments of hydrogen atoms

What are the two phases in chromatography?

Stationary phase (solid) and mobile phase (liquid/gas)

What is the primary use of Gas Chromatography (GC)?

Analysis of volatile compounds and quantitative measurement

When is Simple Distillation used?

When there are large differences in boiling points

When is Fractional Distillation used?

When boiling points are close together

When is Steam Distillation used?

For heat-sensitive

immiscible compounds

How does the boiling point of an immiscible mixture compare to its individual

components?

It is lower than either component alone

When is short path distillation typically used?

It is used for small amounts of material and high boiling point compounds.

What determines the number of signals in an NMR spectrum?

The number of unique proton environments.