chem notes.pdf

8
Under acidic conditions, the aldehyde is oxidized to a carboxylic acid. Under alkaline conditions, this couldn't form because it would react with the alkali. A salt is formed instead. The reaction of primary halogenoalkanes with ammonia: The reaction happens in two stages. In the first stage, a salt is formed - in this case, ethylammonium bromide. This is just like ammonium bromide, except that one of the hydrogens in the ammonium ion is replaced by an ethyl group. There is then the possibility of a reversible reaction between this salt and excess ammonia in the mixture.the ammonia removes a hydrogen ion from the ethylammonium ion to leave a primary amine - ethylamine.The more ammonia there is in the mixture, the more the forward reaction is favoured. The reaction of tertiary halogen alkanes with ammonia, however, this mechanism involves an initial ionization of the halogenoalkane

Upload: alihassanmushtaq

Post on 27-Sep-2015

65 views

Category:

Documents


6 download

DESCRIPTION

Chem notesfor ed edexcelhav everythingcompiled

TRANSCRIPT

  • Under acidic conditions, the aldehyde is oxidized to a carboxylic acid. Under alkaline conditions, this couldn't form

    because it would react with the alkali. A salt is formed instead.

    The reaction of primary halogenoalkanes with ammonia:

    The reaction happens in two stages. In the first stage, a salt is formed - in this case, ethylammonium bromide. This is just

    like ammonium bromide, except that one of the hydrogens in the ammonium ion is replaced by an ethyl group.

    There is then the possibility of a reversible reaction between this salt and excess ammonia in the mixture.the ammonia

    removes a hydrogen ion from the ethylammonium ion to leave a primary amine - ethylamine.The more ammonia there

    is in the mixture, the more the forward reaction is favoured.

    The reaction of tertiary halogen alkanes with ammonia, however,

    this mechanism involves an initial ionization of the

    halogenoalkane

  • A nucleophile is a species (an ion or a

    molecule) which is strongly attracted to a

    region of positive charge in something

    else.Nucleophiles are either fully negative

    ions, or else have a strongly - charge

    somewhere on a molecule. Common

    nucleophiles are hydroxide ions, cyanide

    ions, water and ammonia.

  • Carboxylic acids are compounds which contain a -COOH group

    In aldehydes, the carbonyl group has a hydrogen atom attached to it together with either

    a second hydrogen atom

    Or, a hydrocarbon group which might be an alkyl group or one containing a benzene ring.

    Where aldehydes and ketones differ?

    An aldehyde differs from a ketone by having a hydrogen atom attached to the carbonyl group. This makes the aldehydes very easy to oxidize.

    For example, ethanal, CH3CHO, is very easily oxidized to either ethanoic acid, CH3COOH, or ethanoate ions, CH3COO-.

    Ketones don't have that hydrogen atom and are resistant to oxidation. They are only oxidized by powerful oxidising agents who have the ability to break carbon-carbon bonds.

    Reaction between halogenoalkanes (haloalkanes or alkyl halides) and ammonia

    1}

  • Colour of the Flame tests and how to carry it out

    Clean a platinum or nichrome (a nickel-chromium alloy) wire by dipping it into concentrated hydrochloric acid and then holding it in a hot Bunsen flame. Repeat this until the wire doesn't produce any colour in the flame.When the wire is clean, moisten it again with some of the acid and then dip it into a small amount of the solid you are testing so that some sticks to the wire. Place the wire back in the flame again.

    4}

    3

    2

  • Dilute HCL/H2SO4

    Action of acid Likely Cause

    Carbon di oxide evolved Carbonate or Hydrogen carbonate

    Nitrogen di oxide evolved Nitrite

    Sulphur di oxide evolved on warming Sulphite

    Hydrogen evolved A Metal

    Barium Chloride Solution

    Barium chloride forms a precipitate with a number of ions but usually is a test for sulphate ions

    Anion Precipitate Addition of dilute HCL

    Colour Formula

    Suplate White BaSO4 ppt is insoluble

    Sulphite White BaSO3 ppt dissolves

    Carbonate White BaCO3 ppt dissolves with effervescence

    If Dilute HCL is added to the anion solution before aqueous barium chloride then only sulphate will form a ppt

    Silver Nitrate Solution

    Anion Precipitate Addition of Aqueous NH3

    Colour Formula Dilute Concentrated

    Chloride White AgCL Soluble -----------------------------

    Bromide Cream AgBr Slightly Soluble Soluble

    Iodide yellow AgI Insoluble Insoluble

    Notice the

    trend from

    up to down

    the group

  • Halogen In pure form In non-polar solvents In water Fluorine Pale yellow gas (Reacts with solvents) (Reacts with water) Chlorine Pale green gas Pale green solution

    Pale green solution

    Bromine Dark red liquid Orange solution

    Orange solution

    Iodine Grey solid Purple solution (Insoluble) but forms a brown solution if excess KI is present

    Hydroxides

    Solubility increases down Group II: The hydroxide ion is quite small, and therefore the lattice energy is strongly affected by cation

    size. The decrease in lattice energy down the Group outweighs changes in the hydration enthalpy.

    Sulphates

    Solubility decreases down Group II: The sulphate ion is quite large, and therefore the effect on the lattice energy by the changing cation size is small. The hydration enthalpy decreases down the group as the ions get bigger

  • Heating

    Under reflux

    Separating

    funnel

    Distillation apparatus

    Shd not be air tight and position

    thermometer at point where gas leaves

  • The effect of heat on the Group 2 carbonates

    All the carbonates in this Group undergo thermal decomposition to give the metal oxide and carbon dioxide gas. Thermal

    decomposition is the term given to splitting up a compound by heating it.All of these carbonates are white solids, and the oxides that

    are produced are also white solids.If "X" represents any one of the elements:As you go down the Group, the carbonates have to be

    heated more strongly before they will decompose.The carbonates become more stable to heat as you go down the Group.

    The effect of heat on the Group 2 nitrates

    All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen.

    The nitrates are white solids, and the oxides produced are also white solids. Brown nitrogen dioxide gas is given off together with

    oxygen. Magnesium and calcium nitrates normally have water of crystallisation, and the solid may dissolve in its own water of

    crystallisation to make a colourless solution before it starts to decompose.

    Again, if "X" represents any one of the elements:As you go down the Group, the nitrates also have to be heated more strongly before

    they will decompose.The nitrates also become more stable to heat as you go down the Group.

    Summary

    Both carbonates and nitrates become more thermally stable as you go down the Group. The ones lower down have to be heated more

    strongly than those at the top before they will decompose.