Organic Chemistry Lab Midterm Flashcards
Define eutectic point
The lowest point where the mixture has a very narrow range (in terms of melting point graph). Also the point at which two solids of liquid solution are at equilibrium (with regard to two solids in liquid solution).
3 applications that utilize the melting point of measurements
- Identify unknowns
- Evaluate purity
- Calibrate machines
Explain why it’s important to calibrate the thermometer and the melting point apparatus
It’s important since inaccurate readings can mess up an experiment or misidentify the compounds so that when using these devices one can get accurate melting point by eliminating system errors
Why does NaCl melt at a much higher temperature than glucose
Ionic bonds are harder to change the state of
How can you tell if a compound is pure or not from its melting point?
Impurities lower the melting point and range of the compound
Melting point of biphenyl
69-70 C
Melting point of mandelic acid
120-121 C
Melting point of benzoic acid
122-123 C
Melting point of malic acid
131-132 C
Melting point of cinnamic acid and urea
132-133 C
Melting point of sebacic acid
133-135 C
Melting point of benzoin
135-136 C
Melting point of malic acid
137-139 C
Ethanol is a good solvent for …
Nonpolar compounds
Water is a good solvent because
It is polar and therefore dissolves polar substances well
How are benzoic crystals shaped?
Flat, white crystals
Oiling out occurs when …
Coalescence continues to complete separation (breakdown) of the emulsion, which causes an oily substance to emerge.
Boiling chips are often used when a solvent is heated to a boil because …
It helps the substance boil evenly and prevents burping, using more than one can cause loss of crystals.
Why is it sometimes necessary to filter a hot solution?
This helps filter out any insoluble impurities.
Is boiling the recrystallization solution for a very long time necessary? Does this impact the outcome?
It is not necessary, and it can affect the composition of the substance.
Define boiling point
The temperature at which a liquid changes to a gas
Why should the side arm be placed deep in the receiving vial?
To prevent as much loss of the product as possible via escaping as a gas
Why is experimental boiling point lower than literature?
This is due to a pressure difference because we are at a higher elevation. Lower elevation (greater atmospheric pressure) = higher boiling point.
Single most important variable that contributes to an effective separation of liquids by distillation
Distillation rate
Explain why during distillation the first few drops are cloudy
First drops wash water off the condenser and appear cloudy
Charcoal is used to …
Remove color
Which is more polar; benzoic acid or acetanilide?
Benzoic acid
Because benzoic acid is more polar we have to use NaOH
Because it is a more polar solvent
Benzoic acid is more acidic because
The pKa value is lower
Why are drying agents used?
They remove trace amounts of water that are dissolved in an organic solvent
Dilution equation
M1V1=M2V2
Why do you not use excess drying reagent?
It results in loss of desired product and generates more chemical waste
If the density of the organic layer is not known, explain how you can tell which layer is aqueous and which is organic.
Funnel a drop of water down the tube and observe which layer it goes to.
What does cloudiness in the organic layer indicate in extraction, and how can it be removed?
It indicates presence of small amounts of water, and it’s removed by adding a drying agent.
Criteria for a good extraction solvent
- Ability to selectively dissolve the compound
- Must not react with the compound
- Must be immiscible
