CHM 235 Houtchens Final
Mass of a compound is 1.25g, the volume is 3.75 mL. What is the density?
1.25/3.75 = 0.33 g/mL
Carboxylic acid structure
Acidic
If 5 RF values can be measured on the paper after the separation is complete, how many different compounds are present?
At least 5, but there can be more because some of the different compounds can still have the same RF values
Leaving group is...
Atom (or group of atoms) that leave the molecule (i.e. weak bases, halides)
Which halide behaves as the best leaving group, bromine or chlorine?
Bromine because it is a weaker base as a leaving group
If NaHCO3 (sodium bicarbonate) is added to a solution containing an alcohol, a phenol, an amine, and a carboxylic acid. Which compound would be deprotonated?
Carboxylic acid is the strongest acid so it will be deprotonated. The alcohol + phenol are not strong enough acids to react with sodium bicarbonate. An amine is a base so there would be no reaction.
Compounds A, B, and C are developed on chromatography paper. The solvent front traveled 10 cm. Compound A traveled 9.5 cm, Compound B traveled 3.2 cm, and Compound C traveled 7.1 cm. Rank the polarity of each compound
Compound A = 9.5/10 = 0.95 Compound B = 3.2/10 = 0.32 Compound C = 7.1/10 = 0.71 B most polar, then C, then A is least polar. remember higher RF values means its the least polar, while lower RF values mean its the most polar
2 things that need to be included in pre-lab for each chemical?
Density + Melting point
Benzoic acid more soluble in water or Dichloromethane?
Dichloromethane - like dissolves like
Retention factor
Distance of the band/Distance of the solvent
Base...
Donates electrons to a hydrogen atom
Nucleophile...
Donates its electrons to central atoms (i.e. atoms other than hydrogen), typically stronger with increasing negative charge
Substrate is...
Electrophile (often an alkyl halide) undergoing substitution or elimination
When the chromatography paper is placed in the developing chamber, its imperative that the solvent does not submerge the spots. Why?
Everything will mix + you will not get a good separation
A student wanted to separate a mixture if hexane (BP = 69), 1-pentanol (BP 137.5), acetic acid (BP 118). Explain process to separate these 3 compounds
Fractional distillation. Solution would boil, the vapor would move through the vaporization condensation cycles, then cool down to a liquid and fall into the collection flask. The solutions boil from lowest BP to highest BP, so hexane would boil first, then acetic acid, then 1-pentanol
What would be a possible melting point range for a mixture between a compound with a melting point of 50 degrees celsius and another compound with a melting point of 60 degrees celsius?
It would be lower than the MP for either compound. MP for the mixture will be broader in range, from 42-47 degrees
3 types of lab protection worn at all times?
Lab coat, closed toed shoes, goggles
Sn2 are faster with...
Less substituted substrates Prefers primary
Intensive properties are...
Melting point, boiling point, density
Benzoic acid has a MP of 121-121. Unknown compound was mixed with a pure sample of benzoic acid and the MP of the mixture was 111-118. Is the unknown benzoic acid?
No, it is not Benzoic acid. The temperature dropped + broadened, which shows there were impurities and the compound is not pure Benzoic acid. If it was, the temperature would have stayed in a sharp range and would have not dropped.
If two compounds of a mixture have the same RF value, are they the same compound?
No, they have different absorbances, so they are different compounds. Different compounds can have the same RF value
Why did we use pencil to make the original line on the chromatography paper?
Pencil instead if pen because pen is an organic substance so it would have traveled up the paper
Why is it dangerous to heat an organic compound in a distillation apparatus that has no vent or opening to the atmosphere?
Pressure will build up with the heat + the apparatus can explode + release the harmful vapor of the organic compound into the air
Gravity filtration pros + cons
Pro: able to work at high temps Con: slow + not good for low BP's
Vacuum filtration pros + cons
Pro: works quickly Con: Can't work at high temps
How can volume be measured with the displacement method?
Put 20ml water in a graduated cylinder. Place the item into the water. Measure difference between the initial and final measurement.
Strength of intermolecular forces?
(strongest) ionic > hydrogen bonding > dipole-dipole > london dispersion (weakest)
Student recrystallizes 0.37g of acetanilide. Recover 0.21g. What is the % recovery of acetanilide?
0.21g / 0.37g * 100 = 56.7%
List 3 precautions you can take to safely setup your distillation apparatus:
1) Clamp the round bottom flask 2) Keep tubes away from the hot plate 3) Secure the water condensor with rubber bands
Indicate the correct order of steps for the mixed melting point experiment. Label each with a number 1 - 5
1) Measure the melting point of the unknown compound. 2) Find known compounds with a similar melting point to the unknown 3) Create mixtures of the unknown with each of the matching known compounds. 4) Measure the melting point of the mixtures. 5) Identify the unknown based on the mixture melting points
List and briefly describe the two main steps required to separate an acid from a mixture of organic compounds
1) add an aqueous base to the organic layer + separate 2) add an aqueous acid to the aqueous layer + filter the solid
Process of recrystallization
1) dissolve solute into boiling solvent 2) slowly cool to room temp 3) scratch inside of flask 4) place in ice bath 5) vacuum filtration to separate crystals + recover them
What structural features influence the solubility of soaps?
1) length of the carbon chain. shorter carbon chains = more soluble, longer carbon chains = less soluble 2) degrees of unsaturation cause the soap to be more soluble 3) size of the cation (+). larger cations make the soap more soluble
Which two reaction types compete most readily with one another?
Sn1 + E1
Mobile phase
Substance that carries compounds through the stationary phase
Stationary phase
Substance where separation
Distillation process:
The liquid is place in a round bottom flask. It's heated until it approaches its BP. Vapors collect inside the flask and pass into the condenser. The vapor condenses and is collected in a collection flask.
Why water is run against gravity in the condenser?
To ensure it remains full of liquid and does not operate to cool gas as well. We wanted equal cooling of the vapor with no air pockets
What type of regiochemistry is observed in the E1 reaction
Zaitsev
Benzoic acid behaves like a ______ and is soluble in the ______ layer
acid + organic layer
Mass is...
amount of matter in an object
Solubility is...
amount of solute that will dissolve in a solvent
Mass can be measured with...
an electronic balance
The separatory funnel contains the benzoic acid/acetanilide mixture in dichloromethane and aqueous sodium hydroxide. After shaking the funnel, the contents were given time to settle and two layers formed as a result. The top layer is ______ and the bottom layer is ______
aqueous, organic
linear polymers
are straight carbon chains
sodium hydroxide behaves like a ______ and is soluble in the ______ layer
base + aqueous layer
Isomers...
compounds with same molecular formulas
stereoisomers are...
compounds with the same molecular formula, same bond connections, different spatial arrangements of atoms
water behaves like a ______ and is soluble in the ______ layer
conjugate acid + aqueous layer
Sodium Benzoate behaves like a ______ and is soluble in the ______ layer
conjugate base + aqueous layer
Polyester with glycol created a ________ polymer
cross-linked
As the polarity of a compound increases, the distance it travels up the chromatography paper....
decreases
When two compounds are mixed, the melting point of the mixture will ______ and ________ compared to the melting points of the individual compounds.
drop and broaden
% Recovery
final mass/initial mass * 100
Which compound would be isolated first, second, and third in a distillation? 1-chlorobutane (bp 70) toluene (bp 110) diethyl ether (bp 40)
first diethyl ether, then 1-chlorobutane, then toluene separate from lowest to highest temp
Solvent front
furthest distance traveled by the solvent
The stronger intermolecular forces have the ______ BP's
higher
Physical properties identify the...
identity + purity of a compound
Higher RF values means...
its less polar because it traveled father, so it did not have as much affinity to the origin
Lower RF values means...
its more polar because it traveled less, so it had a higher affinity for the origin
Polyester with ethylene glycol created a ________ polymer
linear
Solubility should be...
low at low temps + high at high temps
Extensive properties include...
mass + volume
Density is...
mass/volume
Distillation is...
method for separating + purifying liquids
SN1, E2, and E1 reactions are faster with...
more substituted substrates prefers tertiary
Enantiomers are...
non-superimposable mirror images all groups change direction
Diastereomers are...
non-superimposable non-mirror images one or some of the groups changes direction, but not all
An ideal solvent is...
non-toxic, readily available, low cost
chiral
not symmetrical, optically active
Would a polar compound have a higher Rf value if it is developed using octane or ethanol as the solvent?
octane is nonpolar, 8 c-c bonds Ethanol is polar, so ethanol would give a higher RF value than octane
How many steps are involved in a bimolecular nucleophilic substitution reaction (SN2)?
one step because both the nucleophile + substrate are involved in the rate determining step
branched polymers
points where the chain goes in a different direction
_______ is the most important property in thin layer chromatography
polarity
What type of solvent is preferred for a unimolecular nucleophilic substitution reaction (SN1)? Why?
protic because it helps solvate the carbocation intermediate + leaving group
Conformational isomers are...
same molecular formulas, same connectivity, different rotational energies (most stable) anti, gauche, eclipsed, fully eclipsed (least stable)
Constitutional isomers are...
same molecular formulas, same energies, different places of attachment
Vacuum filtration is used to...
separate crystals from the mother liquid
Recrystallization is a technique used to...
separate impurities from a compound
Chromatography
separation technique that involves a stationary phase + mobile phase
Pure substances have ______ MP ranges
sharp
What to look for in an extraction solvent?
solute must be more soluble in one of the solvents than the other the two solvents must be miscible or soluble with one another solvent should have a low BP
achiral
symmetrical, not optically active
Melting point is...
temp at which equilibrium is reached between the solid phase and the liquid phase
Will a tertiary alkyl halide or primary alkyl halide react fastest in a bimolecular elimination reaction (E2)?
tertiary because they form more highly substituted alkenes and these are more stable products
Volume is...
the amount of space an object occupies
Why does adding saturated sodium chloride cause the soap to precipitate?
the dissolved
When measuring a melting point, the melting point range begins when...
the first drop of liquid forms and ends when the entire sample is liquid
Eutectic point is...
the lowest MP of a mixture
saturated is...
the max amount of solute for an amount of solvent
solution is...
the mixture of solute + solvent
Distribution coefficient is...
the ratio of the solubilities
What happens when two solvents are immiscible?
they are not soluble with one another so the two liquids will separate into layers based on their densities
liquid-liquid extraction are used to...
transfer a solute from one solvent into another
If the MP of the mixture is the same temp and same range as that of your unknown...
unknown sample is same as authentic sample
solute is...
what is being dissolved
solvent is...
what is dissolving the solute