Alcohols, Haloalkanes & Analysis Flashcards
Explain why alcohols have a higher solubility and lower volatility than ankanes of similar chain lengths.
- When you mix alcohols with water, H-bonds form between the hydroxyl group and the water molecules.
- Alcohols also form H-bonds with each other, which are stronger than the ID-ID interactions between the alkane molecules, so more E is needed to overcome the IM attractions, so they are less volatile.
Explain the trend in solubility of alcohols as chain length increases.
- As length increases, more of molecule becomes non-polar chain.
- ID-ID interactions become stronger and outweigh the H-bonds that the alcohol could form with water, so they become less soluble.
Order the carbon-halogen bonds from weakest to strongest.
C-I, C-Br, C-Cl, C-F
lowest bond enthalpy to highest.
What is a nucleophile?
An electron pair donor.
What are CFCs (give properties).
- Chlorofluorocarbons (only carbon, chlorine and fluorine - all H replaced):
- stable, volatile, non-flammable and non-toxic
How did CFCs damage the environment (give equations).
- Catalysed the break down of ozone into diatomic oxygen.
- They absorb UV radiation, causing the C-Cl bond(s) to break and forming chlorine radicals.
- Cl ˙(g) + O3(g) → O2(g) + ClO ˙(g)
- ClO ˙(g) + O(g) → O2(g) + Cl ˙(g)
- Overall: O3(g) + O(g) → 2O2(g)
As the chlorine radical is regenerated, it can go on to catalyse thousands of other breakdowns before forming a stable compound.
What is the advanced greenhouse effect and what has it caused?
- Gases such as CO2 and methane are being released into atmosphere at far above natural amounts due to increasing industrialisation and burning of fossil fuels.
- They contain C=O, C-H and O-H bonds, which can absorb IR radiation from the Sun and re-emit it in all directions, effecctively trapping heat within the atmosphere.
- Rising average global temps. have caused the shrinking of the polar ice caps and an increased frequency of extreme weather events such as hurricanes.
Why is it preferable to use electrical heaters when refluxing?
Avoid igniting volatile & flammable compounds
How can you purify a volatile liquid?
- Heat with distillation
- If desired product has lower b.p. than impurities, heat until thermometer shows b.p. of product then collect all the liquid that is ditilled until the thermomenter starts to change temp. again, showing the product has all been collected.
- If desired product has a higher b.p. than impurities, collect the second liquid to be distilled.
How do you remove water-soluble impurites from an organic (liquid) product?
- Once reaction is finished, pour mixture into separating funnel and add water.
- Close tap and invert funnel multiple times before allowing layers to settle.
- Organic layer will be less dense than the aqueous layer, so should float on top.
- Open stopper and allow aqueous layer to run out, leaving your purified product.
- Add anhydrous salt to the remaining organic liquid, to bind to any traces of water left, drying the product. All water has been absorbed when salt stops becoming lumpy when you add it. Then filter.
How can you purify a solid organic product?
- Dissolve the impure solid in a minimum of hot solvent.
- Filter solution under reduced pressure [in a Buchner funnel] to remove insoluble impurities.
- Cool solution slowly, allowing crystals of pure product to form and filter again.
- Wash crystals with cold solvent.
- Dry by placing in an oven/ using paper towel.
Outline the 3 methods of checking the purity of a sample.
- Melting point:
- Obtain melting point
- Compare to known values.
- Pure sample will have a sharp melting point very close to database values.
- Spectroscopy:
- Run an NMR/IR spectrum
- Compare to database
- Spectrum of pure sample will contain same peaks as in database and no others.
- TLC:
- Run a TLC
- Compare Rf value to known data
- Pure sample will have very similar Rf
