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Exam Focus:
Covalent bonding, tetravalency, catenation, hydrocarbons,
saturated and unsaturated compounds, homologous series,
nomenclature, functional groups, chemical reactions,
ethanol, ethanoic acid, soaps and detergents.
A. Very Short Answer Questions
Question 1
What is the valency of carbon?
Carbon has a valency of four.
Question 2
What is catenation?
Catenation is the ability of an element to form bonds with
atoms of the same element to produce chains, branches or rings.
Question 3
What is a hydrocarbon?
A hydrocarbon is a compound made up of carbon and hydrogen only.
Question 4
What is a homologous series?
A homologous series is a family of organic compounds having
the same functional group and similar chemical properties,
in which consecutive members differ by a CH₂ unit.
Question 5
What is the functional group present in ethanol?
The hydroxyl group, –OH.
B. Covalent Bonding
Question 6
Why does carbon form covalent bonds?
Carbon has four valence electrons. Losing or gaining four
electrons is energetically difficult, so carbon generally
achieves stability by sharing electrons and forming covalent
bonds.
Question 7
Why does carbon form a large number of compounds?
Carbon forms strong bonds with itself and with many other
elements. Its tetravalency and catenation allow the formation
of chains, branches and rings with many different structures.
Question 8
How many covalent bonds are present in methane?
Methane, CH₄, contains four C–H covalent bonds.
C. Hydrocarbons
Question 9
Differentiate between saturated and unsaturated hydrocarbons.
Saturated hydrocarbons contain only carbon-carbon single bonds.
Unsaturated hydrocarbons contain one or more carbon-carbon
double or triple bonds.
Question 10
Give one example each of an alkane, alkene and alkyne.
Alkane → Ethane, C₂H₆
Alkene → Ethene, C₂H₄
Alkyne → Ethyne, C₂H₂
Question 11
Write the general formula of alkanes.
CₙH₂ₙ₊₂
Question 12
Write the general formulae of alkenes and alkynes.
Alkenes → CₙH₂ₙ
Alkynes → CₙH₂ₙ₋₂
D. Homologous Series & Nomenclature
Question 13
Why do consecutive members of a homologous series differ by
CH₂?
Each successive member contains one additional carbon atom
and two additional hydrogen atoms compared with the previous
member.
Question 14
What is the molecular mass difference between consecutive
members of a homologous series?
The difference is 14 u because CH₂ has a relative molecular
mass of 14 u.
Question 15
Name the compound CH₃CH₂OH.
Ethanol.
Question 16
Name the compound CH₃COOH.
Ethanoic acid.
E. Functional Groups
Question 17
What is a functional group?
A functional group is an atom or group of atoms that gives
an organic compound its characteristic chemical properties.
Question 18
Identify the functional group in CH₃COOH.
Carboxylic acid group, –COOH.
Question 19
Identify the functional group in C₂H₅OH.
Alcohol or hydroxyl group, –OH.
F. Chemical Reactions of Carbon Compounds
Question 20
What is combustion?
Combustion is a reaction in which a substance reacts with
oxygen, usually releasing heat and often light.
Question 21
Write the complete combustion equation for methane.
CH₄ + 2O₂ → CO₂ + 2H₂O + Energy
Question 22
What is an addition reaction?
An addition reaction is a reaction in which atoms or groups
are added across a carbon-carbon double or triple bond.
Question 23
Give an example of an addition reaction.
Question 24
What is a substitution reaction?
In a substitution reaction, one atom or group in a compound
is replaced by another atom or group.
G. Ethanol
Question 25
Write the molecular formula of ethanol.
C₂H₅OH
Question 26
What happens when ethanol is oxidised?
Ethanol can be oxidised to ethanoic acid using a suitable
oxidising agent.
CH₃CH₂OH + 2[O] → CH₃COOH + H₂O
H. Ethanoic Acid
Question 27
What is vinegar?
Vinegar is a dilute aqueous solution of ethanoic acid.
Question 28
Write the reaction of ethanoic acid with sodium
hydrogencarbonate.
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
Question 29
What is esterification?
Esterification is a reaction in which an alcohol reacts with
a carboxylic acid in the presence of an acid catalyst to form
an ester and water.
Question 30
Write the esterification reaction between ethanol and
ethanoic acid.
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
I. Soaps and Detergents
Question 31
What are soaps?
Soaps are generally sodium or potassium salts of long-chain
fatty acids.
Question 32
What is a micelle?
A micelle is an aggregate of soap molecules in water in which
the hydrophobic tails are directed towards oily material and
the hydrophilic ends remain associated with water.
Question 33
Why does soap not work efficiently in hard water?
Calcium and magnesium ions in hard water react with soap to
form insoluble substances called scum, reducing the cleansing
action of the soap.
Question 34
Why are detergents more effective than soaps in hard water?
Detergents generally do not form insoluble scum with calcium
and magnesium ions in the same way as soaps and therefore
retain better cleansing action in hard water.
J. Reasoning-Based Questions
Question 35
Why can carbon form chains of great variety?
Carbon-carbon bonds are strong and carbon is tetravalent.
Therefore, carbon can form straight chains, branched chains
and rings containing many atoms.
Question 36
Why are covalent carbon compounds generally poor conductors
of electricity?
Most molecular covalent compounds do not contain freely
moving ions or electrons capable of carrying electric charge
through the substance.
Question 37
Why does hydrogenation of vegetable oils change their
physical properties?
Hydrogenation adds hydrogen across carbon-carbon double bonds,
converting some unsaturated compounds into more saturated
compounds and changing their physical properties.
Question 38
Why are detergents commonly preferred over soaps for washing
clothes in hard water?
Detergents generally remain effective in hard water because
they do not produce the same insoluble calcium and magnesium
scum that reduces the efficiency of soaps.
K. Competency-Based Practice
Question 39
Compound A contains only carbon and hydrogen and has a
carbon-carbon double bond. What type of hydrocarbon is A?
A is an unsaturated hydrocarbon and belongs to the alkene
family if it contains a carbon-carbon double bond as its
characteristic multiple bond.
Question 40
Two compounds have the same functional group but different
carbon-chain lengths and differ successively by CH₂. What
relationship do they have?
They are members of the same homologous series.
Question 41
A student adds soap to a sample of hard water and observes
curdy material. What causes this observation?
Calcium and magnesium ions in the hard water react with soap
molecules and form insoluble scum.
Question 42
Compound X reacts with an alcohol to produce a sweet-smelling
substance and water. Identify the type of reaction.
It is an esterification reaction. The sweet-smelling product
is an ester.
L. Long Answer Questions
Question 43
Explain the versatile nature of carbon.
Carbon shows tetravalency and catenation.
Because carbon can form four covalent bonds and strong
carbon-carbon bonds, it can make straight chains, branched
chains and ring structures. It can also combine with many
other elements, resulting in a very large number of compounds.
Question 44
Explain the cleansing action of soap.
Soap molecules have a hydrophilic end and a hydrophobic
hydrocarbon end.
The hydrophobic end interacts with oily dirt while the
hydrophilic end interacts with water. Soap molecules arrange
around oily dirt to form micelles, allowing the dirt to be
carried away with water.
Question 45
Explain the important chemical reactions of carbon compounds.
Important reactions include combustion, oxidation, addition
and substitution.
Combustion occurs when carbon compounds burn in oxygen.
Oxidation can convert alcohols into carboxylic acids.
Addition reactions occur mainly with unsaturated compounds.
Substitution reactions are characteristic of saturated
hydrocarbons under suitable conditions.
M. Quick Revision Questions
-
Why does carbon form covalent bonds?
-
Explain tetravalency and catenation.
-
Differentiate between saturated and unsaturated
hydrocarbons.
-
What is a homologous series?
-
Identify important functional groups.
-
Write the oxidation reaction of ethanol.
-
Explain esterification.
-
Why does soap form scum in hard water?
-
Explain micelle formation.
-
Why are detergents effective in hard water?