Chem 308 Discussion
Process of recrystallization:
The crude solid mixture is fully dissolved in the minimum amount of hot solvent (at boiling point). Upon slow cooling, the solubility of the compound decreases, so it crystallizes. Because the impurities are present at low concentrations, they stay in the solution and can be removed by filtration.
How do you use a drying agent?
The crystals form larger clumps when they absorb water.
In distilation, what boils first?
The most volatile substance.
What does a distillation head (and claisen adapter) look like?
kind of like a glass tube faucet
What does it mean if a compound is corrosive?
A corrosive compound is a compound with the ability to eat away things it touches, or cause destruction/alterations to wherever it touches something.
What is the purpose of drying agents?
A drying agent is a chemical used to remove water from an organic compound that is in solution.
What is a flash point?
A flash point is the lowest possible temperature that a liquid can make an ignitable mixture in the air near the liquid.
What solvent would you use in recrystallization if your unknown was soluble in ethanol and insoluble in water?
A mixture of both ethanol and water (you want a solvent that the unknown is partially soluble in).
What is an azeotrope?
A mixture of liquids with a definite composition that distills at a constant temperature without a change in the composition.
What is BP?
Boiling point, measured in Celsius.
What kind of waste goes in the nonhalogenated waste disposal?
Compounds that do not contain fluorine, chlorine, bromine, or iodine.
What is the first thing you should do when a chemical is spilled on your skin?
Dilute immediately using cold tap water (not hot) and notify your instructor.
What kind of waste goes in the halogenated waste disposal?
Halogenated refers to a chemical compound or mixture that contains halogen atoms, i.e. fluorine, chlorine, bromine, or iodine.
What is density?
How heavy something is, weighed in grams per milliliter.
What is solubility?
How well something mixes completely with another substance.
What is Rf?
Retention factor.
What does a connecter with a support rod look like?
Rubber connecter with a rod coming out of it.
What does a connecter look like?
Rubber thing to hold things together.
What does septum look like?
Rubber, looks like the end of a marker.
What does flammable mean?
Something that is easily set on fire.
What is normal atmospheric pressure?
760mm
What is an irratant?
A substance that causes slight inflammation or another discomfort to the body.
Interpret this: i H2O; msc EtOH; s eth.
Insoluble in water. Miscible in ethanol. Soluble in ether.
What does it mean if a compound is a lachrymator?
If a compound is a lachrymator, it means if you are exposed to that compound or inhale it, it will cause tears/your eyes to water.
What does it mean if a compound is toxic?
If a compound is toxic, it is harmful to you (or the environment) if inhaled, ingested, or absorbed through your skin.
What does it mean if a compound is carcinogenic?
If something is carcinogenic, that means it is a known substance that causes cancer or is likely to cause cancer. That substance would be called a carcinogen.
When would you use a drying agent?
In making or isolating chemical compounds because they often become contaminated with water.
Where does broken glass go?
In the broken glass container.
If something is the least volatile, that means
It has the highest boiling point.
If something is the most volatile, that means
It has the lowest boiling point.
TLC Visualization: Why would you use permanganate stain?
It is particularly good for alkenes and alkynes. (alcohols, amines, sulfides and other oxidizable groups may require gentle heating).
What does LC50 mean?
It is the lethal concentration required to kill 50% of the population.
What does LD50 mean?
It is the lethal dose required to kill 50% of the population.
What should you do if a chemical is spilled on or around a balance?
It must be cleaned immediately, but notify instructors first and wait for special instructions.
What is MP?
Melting point, measured in Celsius.
What does MW mean?
Molecular weight, measured in grams per mol.
TLC plates, do nonpolar or polar move up faster?
Nonpolar (they have fewer attractive forces on the polar gel).
What does Oral-Rat LD50: 1580 mg/kg mean?
Oral-Rat LD50: 1580 mg/kg means that a 1580 mg dose of a specific chemical per 1 kg of the body weight of a rat, when given one dose by mouth, caused death in 50% of the test group.
What does PS mean?
Physical state, either a solid, liquid, or gas.
Silica gel is
Polar.
What is NDT?
Refractive index, how fast light changes speed as it passes from one medium to another.
How do you find Rf?
The solvent line to the center of the spot/solvent line to the solvent front.
TLC Visualization: Why would you use UV light?
To see UV-active compounds (conjugated double bonds, aromatic compounds).
TLC Visualization: Why would you use p-anisaldehyde stain?
To see strong and weak nucleophilic groups.
What is the main concept of distillation?
To separate two or more miscible liquids based on differences in boiling point
What solvent would you use in recrystallization if your unknown was insoluble in ethanol and partially soluble water?
Water (you want a solvent that the unknown is partially soluble in).
When does a liquid reach its boiling point?
When its vapor pressure is equal to its atmospheric pressure.
When making a TLC plate, do you want a polar or nonpolar solvent?
You want your solvent to be polar (Polar solvents will compete with the compounds for polar sites on the silica gel, causing compounds to move more quickly up the plate).
