HIGHER CHEMISTRY REVISION.

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HIGHER CHEMISTRY REVISION.
Unit 2- Reactions of Carbon Compounds
1. Although aldehydes and ketones have
different structures, they both contain the
carbonyl functional group. (a) In what way
is the structure of an aldehyde different from
that of a ketone?   (b) As a result of the
difference in structure, aldehydes react with
Fehlings (or Benedicts) solution and
Tollens reagent but ketones do not.
What colour change would be observed when
propanal is heated with Fehlings (or
Benedicts) solution? (c) In the
reaction of propanal with Tollens reagent,
silver ions are reduced to form
silver metal. Complete the following
ion-electron equation for the oxidation. C3H6O ?
C2H5COOH   (d) Name the compound with the
formula C2H5COOH.
(a) The carbonyl group is on the end of the
carbon chain in the aldehyde. It is not
on the end of the carbon chain in a ketone. (b)
Colour changes from Blue to orange-red. (c)
C3H6O H2O ? C2H5COOH 2H 2e- (d)
Propanoic acid
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2. As a result of both containing the carbonyl
group, aldehydes and ketones react in a
similar way with hydrogen cyanide. The
equation for the reaction of propanal with
hydrogen cyanide is shown.       (i)
Suggest a name for this type of reaction.
(ii) Draw a structure for the product of
the reaction between propanone
and hydrogen cyanide.
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3. Alkenes can react to produce unstable
compounds called peroxides. These
peroxides break down rapidly to form compounds
which have the same functional groups.
For example, alkene X reacts to produce
compounds Y and Z. (In the following
structural formula R and R are used to
represent different alkyl groups).
O R - C
H Compound Y
H H H H R - C C -
R ? R - C - C - R ?
alkene X O
O O peroxide
R - C
H Compound Z
(a ) To which homologous series do both
compounds Y and Z belong? (b) In one
reaction, alkene X reacts to produce the two
compounds shown below.
O CH3
O CH3 - C CH3 - C -
C H H H
Name alkene X in this
reaction.
O2
(a) Y and Z are both aldehydes. (b)
4-methylpent-2-ene
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4. Propan-2-ol can be prepared from propane as
follows. CH3 CH2CH3 CH3 CH CH2 CH3
CHCH3 O
H condensation
cracking dehydration hydration
hydrolysis oxidation (a) Identify
the name of the type of reaction taking place at
Step 1. (b) Identify the name of the
type of reaction taking place at Step 2.
Step 1
Step 2

1. Cracking.
2. Hydration

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5. Propanone and propanal both contain the same
functional group. (a) Name this functional
group. (b) This diagram show how to
distinguish between propanone and
propanal. Explain what is observed in
the reaction between propanal and Tollens
reagent.
Tollens Reagent

• Carbonyl group.
• A silver mirror forms on the side of the test
  tube.
• The silver ions in the Tollens reagent
  are reduced to silver atoms.
• Ag(aq) e- ? Ag(s)
• The propanal is oxidised to propanoic
  acid.

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6. Peeled apples turn brown due to reactions of
compounds called phenols. The first two
steps in the reaction of one phenol, A, are
- (a) The same type of reaction takes
place in both steps. Give the name of this
type of reaction. (b) The molecular formula for
compound A can be written as C7HxO. What
is the value of x? (c) An enzyme called
phenolase, present in apples, acts as a catalyst
during the browning of apples. It
has been discovered that covering a slice of
apple with lemon juice stops it from going
brown. Suggest a reason for this.

• Oxidation.
• X 8
• (c) The acid changes the pH conditions which
  denatures the enzyme so that it no longer acts as
  a catalyst. When an enzyme is denatured its
  shape is changed irreversibly.