Chem 331 Lab Final Exam and All
Correct Answers 2025-2026 Updated.
When determining the melting point of a compound, which of the following may cause the
observed melting point to differ from the accepted literature melting point? - Answer
Impurities present in the sample will affect the melting point.
Residual solvent or moisture in the sample will affect the melting point.
Rapid heating of the sample will affect the observed melting point.
Impurities present in the sample will affect the melting point.
In this experiment, you will have an organic layer and an aqueous layer in your separatory
funnel. Where will the neutral layer be during the separation of these layers? - Answer The
aqueous layer will contain the neutral compound because the neutral compound is very
nonpolar.
When is an appropriate time to remove your safety goggles during the lab? - Answer When
you are ready to leave the lab.
Which of the following details are critical to the success of analysis using thin layer
chromatography (TLC)? - Answer The sample must be spotted above the surface of the
developing solvent in the developing chamber.
The TLC developing chamber should be covered.
If you spill hydrochloric acid solution on your bench, what is the best way for you to clean the
spill? - Answer Sprinkle some acid neutralizer on the spill, and then wipe the area clean.
Why are methanol and acetone not appropriate organic solvents to be used for extraction with
water? - Answer These solvents are fully miscible with water.
Which of the following actions could result in a false high weight determination of a neutral
solid compound? - Answer Incomplete drying of the organic layer, leaving a mixture of the
desired compound and water (after rotary evaporation).
Incomplete extraction of the other compounds, leaving them mixed with the desired neutral
compound (after rotary evaporation).
, Suppose you have a mixture of two neutral compounds that are solids. One of the compounds is
quite soluble in hexane, whereas the other is insoluble in hexane. However, both compounds
are very soluble in dichloromethane. Which of the following methods will allow separation of
these two neutral compounds? - Answer Adding the mixture to hexane, then isolating the
insoluble compound using filtration.
In which of the following scenarios is TLC analysis useful? (Circle all that apply for full credit.) -
Answer You wish to determine the relative polarities of two different compounds.
You wish to determine if a starting material has been consumed during the course of a reaction.
You wish to determine if an impurity is present in an known sample.
After an organic compound has been extracted from an organic solution as an aqueous salt, it
may not be convenient to precipitate the compound out of aqueous solution by adjusting the
pH. This is particularly true if the organic compound is a liquid. Since water is not readily
removed by rotary evaporation due to its high boiling point. What other method could be used
to isolate the original organic compound? - Answer First, adjust the pH of the aqueous
solution to form the neutral compound. Then extract the compound from the aqueous layer
with an organic solvent. Then remove the organic solvent by rotary evaporation.
Which of the following should you do before you leave the lab for the day? - Answer Remove
your personal protective equipment (PPE's) and wash your hands.
Ensure your lab drawers are locked and your fume hood sash is down.
Submit a copy of your lab report to your TA.
Which statement is false? - Answer A given compound will always have the same Rf value on
a TLC plate, regardless of the developing solvent used.
Dispose of TLC spotter? - Answer yellow glassware container
Which item below is not needed for a vacuum filtration? - Answer capillary tubes
What information can be gained from the infrared spectrum of a compound? - Answer
functional groups are present
The spots on your developed TLC plate have long streaks below them making it difficult to see
the separate spots. What are some possible reasons for this? (Select all correct answers for full
credit.) - Answer too much sample was used
Correct Answers 2025-2026 Updated.
When determining the melting point of a compound, which of the following may cause the
observed melting point to differ from the accepted literature melting point? - Answer
Impurities present in the sample will affect the melting point.
Residual solvent or moisture in the sample will affect the melting point.
Rapid heating of the sample will affect the observed melting point.
Impurities present in the sample will affect the melting point.
In this experiment, you will have an organic layer and an aqueous layer in your separatory
funnel. Where will the neutral layer be during the separation of these layers? - Answer The
aqueous layer will contain the neutral compound because the neutral compound is very
nonpolar.
When is an appropriate time to remove your safety goggles during the lab? - Answer When
you are ready to leave the lab.
Which of the following details are critical to the success of analysis using thin layer
chromatography (TLC)? - Answer The sample must be spotted above the surface of the
developing solvent in the developing chamber.
The TLC developing chamber should be covered.
If you spill hydrochloric acid solution on your bench, what is the best way for you to clean the
spill? - Answer Sprinkle some acid neutralizer on the spill, and then wipe the area clean.
Why are methanol and acetone not appropriate organic solvents to be used for extraction with
water? - Answer These solvents are fully miscible with water.
Which of the following actions could result in a false high weight determination of a neutral
solid compound? - Answer Incomplete drying of the organic layer, leaving a mixture of the
desired compound and water (after rotary evaporation).
Incomplete extraction of the other compounds, leaving them mixed with the desired neutral
compound (after rotary evaporation).
, Suppose you have a mixture of two neutral compounds that are solids. One of the compounds is
quite soluble in hexane, whereas the other is insoluble in hexane. However, both compounds
are very soluble in dichloromethane. Which of the following methods will allow separation of
these two neutral compounds? - Answer Adding the mixture to hexane, then isolating the
insoluble compound using filtration.
In which of the following scenarios is TLC analysis useful? (Circle all that apply for full credit.) -
Answer You wish to determine the relative polarities of two different compounds.
You wish to determine if a starting material has been consumed during the course of a reaction.
You wish to determine if an impurity is present in an known sample.
After an organic compound has been extracted from an organic solution as an aqueous salt, it
may not be convenient to precipitate the compound out of aqueous solution by adjusting the
pH. This is particularly true if the organic compound is a liquid. Since water is not readily
removed by rotary evaporation due to its high boiling point. What other method could be used
to isolate the original organic compound? - Answer First, adjust the pH of the aqueous
solution to form the neutral compound. Then extract the compound from the aqueous layer
with an organic solvent. Then remove the organic solvent by rotary evaporation.
Which of the following should you do before you leave the lab for the day? - Answer Remove
your personal protective equipment (PPE's) and wash your hands.
Ensure your lab drawers are locked and your fume hood sash is down.
Submit a copy of your lab report to your TA.
Which statement is false? - Answer A given compound will always have the same Rf value on
a TLC plate, regardless of the developing solvent used.
Dispose of TLC spotter? - Answer yellow glassware container
Which item below is not needed for a vacuum filtration? - Answer capillary tubes
What information can be gained from the infrared spectrum of a compound? - Answer
functional groups are present
The spots on your developed TLC plate have long streaks below them making it difficult to see
the separate spots. What are some possible reasons for this? (Select all correct answers for full
credit.) - Answer too much sample was used
