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Chem Lab Exam 3
| Question | Answer |
|---|---|
| What information does an IR spectrum provide? | It identifies functional groups within a molecule by measuring molecular vibrations caused by the absorption of infrared radiation |
| Where does the Hydroxyl (O-H) group peak appear? | A strong, broad peak between 3200 and 3650 cm⁻¹ |
| Where does the Carbonyl (C=O) group peak appear? | A very strong, sharp peak between 1650 and 1780 cm⁻¹ |
| How can you distinguish an Aldehyde from a Ketone using IR? | Both have the C=O peak, but aldehydes also have two sharp, weak peaks at 2700 and 2800 cm⁻¹ |
| Where do Alkene (C=C) peaks appear? | Between 1640 and 1680 cm⁻¹ (medium to strong) |
| What is a "neat" IR sample? | A liquid sample prepared by placing a small drop between two KBr salt plates without any solvent |
| Why must KBr salt plates never be cleaned with water? | They are made of salt and will dissolve in water; they must be cleaned with methylene chloride |
| What is the safety risk of Fischer Esterification reactants? | Concentrated Sulfuric Acid (H2SO4) and Acetic Acid are corrosive; avoid skin contact and use gloves |
| In the nutmeg experiment, why was Diethyl Ether used as the solvent? | It is able to extract trimyristin while avoiding other fats and oils, and its low boiling point (35 °C) makes it easy to remove via rotary evaporation |
| According to the study guide, what does the Rf value in TLC represent? | While not detailed in the handouts, the Rf (Retention factor) is the ratio of the distance traveled by the compound to the distance traveled by the solvent, used to identify substances and assess polarit |
| What three components are reacted to form a fruity ester? | A carboxylic acid (acetic acid), an alcohol, and a catalytic amount of acid (sulfuric acid) |
| What is the role of concentrated Sulfuric Acid (H₂SO₄) in the ester synthesis? | It acts as a catalyst to speed up the reaction |
| How was Le Chatelier’s principle used to increase the yield of the ester? | By using an excess of one of the reactants (acetic acid) to shift the equilibrium toward the product |
| What are the two main by-products of the esterification reaction? | Water (H₂O) and any unreacted starting materials |
| Why is the ester layer easy to see in the separatory funnel? | Because the ester is immiscible (does not dissolve) in the aqueous solution, causing it to form a distinct layer |
| What is Trimyristin? | A saturated fat that is a tri-ester composed of glycerol and myristic acid |
| Why was Diethyl Ether used instead of water for the nutmeg extraction? | Diethyl ether is a non-polar solvent that dissolves the fat (trimyristin), whereas water is polar and would not effectively extract the non-polar fats |
| What is the purpose of Rotary Evaporation? | To quickly remove a volatile solvent (like diethyl ether) from a non-volatile product (like trimyristin oil/solid) |
| Why is acetone used during the purification of trimyristin? | Trimyristin is insoluble in cold acetone, allowing it to be collected as a solid during recrystallization/filtration while soluble impurities stay in the liquid |
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