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Chem Lab Exam 2
| Question | Answer |
|---|---|
| What is the definition of Reflux? | A laboratory technique where a reaction is conducted in a boiling solvent at a constant temperature, with vapors being condensed and returned to the flask |
| Why must the top of a reflux condenser remain open? | Capping it would create a closed system, which could lead to pressure buildup and a potential explosion |
| What is the "reflux ring"? | The cloudy or misty ring in the condenser where the rising vapors are cooling and turning back into liquid |
| Why is a heating mantle never plugged directly into a wall outlet? | It must be connected to a variable power supply (controller) to safely regulate the temperature |
| When is Vacuum Filtration used instead of Gravity Filtration? | Vacuum filtration is used to rapidly collect solid products (like trimyristin) from a liquid, whereas gravity filtration is typically used to remove solid impurities from a hot solution |
| What are the key pieces of equipment for Vacuum Filtration? | A filter flask (side-arm flask), a Büchner funnel, a Filtervac adapter, and thick-walled vacuum tubing connected to an aspirator |
| What is the goal of Recrystallization? | To purify a solid compound by dissolving it in a hot solvent and allowing it to slowly crystallize as it cools, excluding impurities from the crystal lattice |
| What type of solvent is chosen for Recrystallization? | One in which the compound is nearly insoluble at room temperature but highly soluble when the solvent is boiling |
| Why is "slow cooling" critical in recrystallization? | Slow cooling allows for the formation of well-structured crystals that exclude impurities; rapid cooling can trap impurities inside the solid |
| What is the purpose of Norit (decolorizing charcoal)? | It is added to a hot solution to remove colored impurities; it is then removed via gravity filtration |
| How should a Melting Point always be reported? | As a range of two temperatures: from when the first crystal starts to melt to when the last crystal is completely liquid |
| How does the presence of an impurity affect the Melting Point? | Impurities typically lower the melting point and broaden the melting point range |
| What is the recommended heating rate when approaching a compound’s Melting Point? | Approximately 2 °C per minute |
| Unlike Boiling Point, does Melting Point change with atmospheric pressure? | No, Melting Point is a physical constant that is independent of atmospheric pressure |
| What is Gas Chromatography (GC)? | A technique used to separate and analyze liquid mixtures by distributing components between a gas mobile phase (Helium) and a liquid stationary phase |
| What is "Retention Time"? | The amount of time it takes for a specific component to pass through the GC column to the detector |
| What is the relationship between Boiling Point and Retention Time in GC? | Generally, compounds with higher boiling points will have longer retention times |
| What does the "peak area" in a GC chromatogram represent? | The area under each peak allows for the determination of the relative percentage of that specific compound in the mixture |
| What two things must you never inject into a GC? | Water or inorganic salts |
Created by:
bbrdd