Midterm Flashcards
What is the eutetic composition for a compound mixture X and Y?
The mass percent of X and Y at the eutetic temperature. Both solid X and solid Y are in equilibrium with the liquid
What is the eutetic temperature of a mixture?
The lowest possible melting point for a mixture of X and Y
Passing directly from solid to vapor without going through the liquid phase is known as
sublimation
A process to remove impurities from organic compounds that are solid at room temperature
recrystallization
What is the ideal solvent in a recrystallization lab?
Ideal solvent: dissolves the compounds/impurities at elevated temperatures, but nearly insoluble at room temperature
What is oiling out?
occurs when a compound is insoluble in a solution at a temperature above the compound’s melting point
What are the 4 criteria for selecting a recrystallizing solvent
- insoluble at room temperature
- soluble at boiling temperature
- solvent boiling point must be lower than the compounds melting point (else oil out)
- abundant quantity of crystals must be recoverable from the cool solvent
What was the purpose of carbon in the recrystallize lab?
Activated carbon or decolorizing carbon is used to remove colored impurities from solution
What is percent recovery?
(mass of final)/ (mass of initial) x 100%
How should you position the thermometer head during a distillation?
The thermometer should be positioned correctly so that the vapor pressure is measured accurately. To record the temperature correctly:
the thermometer should be inserted into the thermometer adapter so that the TOP of the thermometer bulb is even with or slightly below the bottom of the side arm on the distilling head.
What is the purpose of a distillation?
To separate compounds based on differences in boiling points.
What does it mean for a compound to be volatile?
It has a high vapor pressure and low boiling point
What is the result of an increase in heating rate of a boiling compound?
The temperature doesn’t change but the rate at which vapor is produced from the liquid increases
What is the difference between simple and fractional distillation?
Simple distillation can be used when the boiling points of two compounds is GREATER than 40 degrees celsius.
Fractional distillation has the effect of many simple distillations.
On a graph, a fractional distillation has a greater slope than a simple distillation. The temperature of the volatile compound reaches the thermometer which represents a constant horizontal line until the less volatile compound vapors reach the thermometer and a sharp increase in temperature happens.
How do you calculate Rf values?
Rf= distance traveled by compound/ distance traveled by fluent
