WorksheetsE1 Purification of Benzoic Acid
Total questions: 15
Worksheet time: 22mins
Which statement is FALSE about recrystallization as a purification technique?
Exploits difference in solubility of solute in a given solvent at varying temperatures
Exploits difference in solubility of desired compound and contaminants in a given solvent
Exploits the high vapor pressure of a solid at a temperature below its melting point
Exploits the ability of a compound to form pure crystals upon cooling from a saturated solution
Which is NOT a criteria in choosing an appropriate recrystallization solvent?
Desired solute is sparingly soluble at room temperature but soluble at high temperature.
Solvent does not react with the solute.
Solvent is moderately volatile and non-flammable.
Boiling point of solvent is higher than the melting point of the desired solute.
Which of the following statements is NOT true when performing recrystallization?
Adding a small amount of activated charcoal adsorbs colored impurities.
Using a 3:1 filter paper maximizes surface area for faster collection of the filtrate.
Pre-heating the receiving flask prevents premature recrystallization during hot filtration.
Allowing the hot solution to cool slowly promotes crystal growth.
If no recrystallization is observed, which of the following can be done?
If the solution is unsaturated, add a small crystal of pure substance.
If the solution is unsaturated, scratch the walls or bottom of the flask.
If the solution is unsaturated, boil off the excess solvent.
If the solution is unsaturated, mix the solution thoroughly.
Which of the following is TRUE about recrystallization and sublimation?
Recrystallization usually offers higher purity than sublimation.
Sublimation is applicable for a wider range of compounds than recrystallization.
Recrystallization does not require solvent unlike sublimation.
Sublimation usually offers higher purity than recrystallization.
Which of the following will INCREASE the apparent %recovery of recrystallized benzoic acid?
Not adding activated charcoal
Using a fluted filter paper for cold filtration
Not pre-heating the receiving flask for hot filtration
Using a long-stemmed funnel for hot filtration
Which is the BEST recrystallization solvent for solute A?
W
X
Y
Z
If 100 mL of solvent W was used to recrystallize 1.0 g solute A, what will be the %recovery of A?
40%
55%
60%
90%
If 100 mL of solvent Y was used to recrystallize 1.0 g solute A, what will be the %recovery of A?
20%
80%
40%
100%
Caffeine has a theoretical melting point of 235°C. Given the following experimental melting ranges, which sample contains the HIGHEST percentage of caffeine?
Sample A: 229-231°C
Sample B: 232-234°C
Sample C: 226-234°C
Sample D: 224-226°C
During recrystallization, you accidentally introduced excess solvent after hot filtration. What should be your next step to ensure effective recrystallization?
Add more crude sample to the solution.
Filter the solution carefully while it is still hot.
Immediately cool the solution to room temperature before placing in an ice bath.
Heat the solution again to evaporate some of the solvent and then cool.
During sublimation, you notice some crystals are forming at the bottom of the beaker instead of depositing on the filter paper. Which of the following is a possible cause?
Heating was done at an inconsistent temperature.
Heating time was too short.
Heating time was too long.
Heating was done with the beaker tightly covered.
Spongebob, Patrick, Squidward and Sandy recrystallized benzoic acid individually. Who among them is expected to have the LOWEST percent recovery?
Spongebob forgot to add activated charcoal to his solution.
Patrick used hot water to wash the crystals after cold filtration.
Squidward did not use a fluted filter paper during hot filtration.
Sandy did not use a fluted filter paper during cold filtration.
Spongebob, Patrick, Squidward and Sandy recrystallized benzoic acid individually. Who among them is expected to have the WIDEST melting range?
Spongebob forgot to add activated charcoal to his solution.
Patrick used hot water to wash the crystals after cold filtration.
Squidward did not use a fluted filter paper during hot filtration.
Sandy did not use a fluted filter paper during cold filtration.
A mixture containing 11.0 g P and 4.0 g Q is to be purified by recrystallization with 100 mL ethanol. Their solubilities in ethanol (in g/100 mL) are given in the table. What is the %purity of P and Q in the isolated product?
%purityP = 93.6%, %purityQ = 6.36%
%purityP = 89.2%, %purityQ = 10.8%
%purityP = 93.0%, %purityQ = 7.04%
%purityP = 71.3%, %purityQ = 8.67%
