chem notes.pdf
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Chem notesfor ed edexcelhav everythingcompiledTRANSCRIPT
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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
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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.
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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
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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.
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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
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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
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Heating
Under reflux
Separating
funnel
Distillation apparatus
Shd not be air tight and position
thermometer at point where gas leaves
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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.