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18 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Eutectic Point
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The lowest temperature at which a mixture of compounds melts.
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Melting Point
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3 Applications of MP Measurement
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1. Identifying unknown compound
2. Evaluating purity of a SOLID sample 3. Confirm identity of a compound |
Melting Point
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Q: Why is it important to calibrate the thermometer and melting point apparatus?
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A: In order for them to measure temperatures correctly due to deviations in thermometer readings.
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Melting Point
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Q: Explain why a small molecule like sodium chloride melts at 801°C while a much larger molecule like glucose melts at 146°C.
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A: Unlike glucose, which has a hydrogen bond, NaCl is made of an ionic bond which is much stronger than a hydrogen bond and thus requiring more energy (HEAT) to be broken than the amount of energy needed to break down glucose.
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Melting Point
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Melting Point Lab
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Reagents:
Cinnamic Acid Urea Cinnamic Acid/Urea Mixture Equations: Deviation from MP (∆x + ∆y): MP Range of pure-133.25 Correction Coefficient: (∆x+∆y)/2 = °C |
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Describe and explain how the melting point of the mixture of cinnamic acid and urea differ from that of the pure compounds
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Wide MP range indicates impurity.
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Melting Point
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Name the intermolecular attractive forces in benzoic acid
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-Hydrogen Bonds
-London Dispersion Forces -Dipole-Dipole |
Melting Point
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Q: What is the effect of each of the following on the melting point of cinnamic acid?
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-Poor packaging of sample in capillary
A: If there is too much of cinnamic acid within the capillary, it will take a much higher than average temperature to melt the substance, raising the melting point -Wet sample A: Melting point will lower -Insoluble impurities A: Melting point will have a wider range -Fast heating rate A: No effect on melting point |
Melting Point
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Q) Which of the following is expected to have a higher melting point?
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-Anthracene or Napthalene
A: Anthrocene-More H Bonds -Benzoic Acid or Acetanilide A: Benzoic acid-More pure |
Melting Point
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Explain the "oiling out" phenomenon during recrystallization. When does it happen?
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Crystallization products separate not as crystals but as gooey liquid (oil). Occurs when the BP of the solvent is higher than the melting point of the solute
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Recrystallization
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Petroleum Ether
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Mixture of hexane and propane (hydrocarbon mixture) to create a nonpolar solvent benzine
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Recrystallization
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Q: Is there are any danger of using two boiling chips instead of one?
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A: May result in loss of crystals when trying to removing boiling chips
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Recrystallization
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Q: Why is it necessary sometimes to filter the hot solution during recrystallization?
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A: Because sometimes insoluble impurities will need to be removed
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Recrystallization
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Q: Does boiling the solution for very long time during recrystallization do any harm?
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A: Excessive boiling of the solution should be avoided because it results in evaporation of the solvent and may cause decomposition of the organic compound
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Recrystallization
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Recrystallization Lab
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Solvents:
-Water -Ethanol -Petroleum Ether The appropriate solvent for recrystallization is water. Ethanol and petroleum ether did not cause crystallization. Benzoic acid extremely pure following recrystallization. Equations: Percent Recovery: (Weight of Pure Crystals/Weight of Crude)*100 |
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What is the purpose of using charcoal in recrystallization?
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Charcoal is used to remove color from solution and turn the clouded dark substance into one that is clear.
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Recrystallization
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What is the effect of using large excess of charcoal during recrystallization?
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Excess charcoal may bond to substance being purified.
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Recrystallization
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Why is it important to use boiling chips when boiling solutions?
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Prevents overheating
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Recrystallization
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