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Chem Lab Exam 1
Chem Lab Final Exam
| Question | Answer |
|---|---|
| How do you calculate the density of an unknown liquid? | Density is calculated by dividing the mass of the liquid (mass of cylinder + unknown - mass of empty cylinder) by the volume of the liquid in milliliters (g/mL) |
| What is the formula for Percent Yield? | Percent Yield = (Actual Yield in grams / Theoretical Yield in grams) × 100 |
| How do you perform a Boiling Point (BP) correction for Boone, NC? | Because of the high elevation, you must add between 2–6 °C to your observed thermometer reading, or multiply your reading by 1.03, to compare it to literature values |
| What determines the Theoretical Yield of a reaction? | The theoretical yield is the maximum amount of product that could be formed, calculated based on the number of moles of the limiting reagent |
| What is a Limiting Reagent? | It is the reactant that is completely consumed first in a chemical reaction, thereby limiting the amount of product that can be formed |
| What is the general purpose of distillation? | Distillation is the process of purifying or separating a mixture of liquids by vaporizing them in one vessel and condensing the vapors into another vessel |
| When is Simple Distillation most useful? | It is most useful for purifying a liquid that contains non-volatile impurities or small amounts of impurities with significantly different boiling points |
| When is Fractional Distillation preferred over Simple Distillation? | It is used to separate liquid mixtures with boiling points that are closer together, using a vertical fractionating column to improve efficiency |
| How does packing a fractional distillation column (e.g., with glass beads) affect separation? | Packing increases the surface area within the column, allowing for more vaporization-condensation cycles, which results in a sharper separation of components |
| What is the "very important" rule for thermometer placement in a distillation setup? | The top of the thermometer bulb must be aligned with the bottom of the side arm of the three-way adapter to accurately measure the temperature of the rising vapors |
| What is a "good distillation rate" during the collection process? | A rate of approximately 1 drop per second is considered ideal |
| What are the "forerun" drops in a distillation, and what should you do with them? | The first few drops (~5) collected may contain impure portions of the sample and should be collected in a separate beaker, not your final collection vessel |
| What is Liquid-Liquid Extraction? | A technique using two immiscible liquids (usually an organic solvent and water) to separate components based on their relative solubility in each phase |
| In a separatory funnel, which layer is usually on the bottom? | The more dense layer (often the aqueous layer, unless a chlorinated solvent is used) will be at the bottom |
| Why must you "vent" the separatory funnel frequently during shaking? | Shaking can build up internal pressure, especially when using sodium bicarbonate which produces CO2 gas upon reacting with acids |
| What is the purpose of adding 5% sodium bicarbonate (NaHCO3) during an extraction? | It is used to neutralize and remove acidic components (like acetic acid or sulfuric acid) from the organic layer |
| What is the purpose of a drying agent like Calcium Chloride (CaCl2)? | It is added to the isolated organic layer to adsorb any remaining water contamination |
Created by:
bbrdd