1
A group of students is studying different allotropes of carbon. They observe that diamond is extremely hard and used in cutting tools, while graphite is soft and slippery and used as a lubricant. They also note that graphite conducts electricity, whereas diamond does not.(a) Explain why diamond and graphite, being made of only carbon atoms, have such different physical properties. [2 marks](b) Relate the electrical conductivity of graphite to its structure. [2 marks](c) A student incorrectly states that since graphite conducts electricity, it must be a metal. Justify why graphite, despite its conductivity, is classified as a non-metal. 1mark
2
Assertion (A): Carbon compounds are generally poor conductors of electricity.Reason (R): Carbon compounds are formed by sharing of electrons, resulting in the absence of charged particles (ions).(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
3
A fuel station attendant is filling petrol into a car. The petrol is a mixture of hydrocarbons. The attendant notices that some of the petrol evaporates and forms a vapour.(a) Explain why petrol, being a liquid at room temperature, forms vapours. [1 mark](b) The car's engine burns this fuel with oxygen. If the combustion is complete, what are the products formed? [1 mark](c) If the fuel is not burning completely due to insufficient air, what is a likely observation and why? 2marks
4
A student is trying to draw the electron dot structure for methane (). They know that carbon has 4 valence electrons and hydrogen has 1 valence electron.(a) How many shared pairs of electrons will be formed in a methane molecule? [1 mark](b) Draw the electron dot structure for methane. [2 marks](c) Explain how carbon achieves a noble gas configuration in methane. 2marks
5
Assertion (A): Carbon exhibits the property of catenation to a greater extent than silicon.Reason (R): The C-C single bond is stronger than the Si-Si single bond.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
6
A chemistry teacher is demonstrating the properties of saturated and unsaturated hydrocarbons to a class. They burn a sample of methane and then a sample of ethene in the presence of air.(a) Describe the type of flame observed when methane burns and explain why. [2 marks](b) Describe the type of flame observed when ethene burns and explain why. [2 marks](c) What observation would be made if a metal plate were held over the burning ethene flame? What does this indicate? 1mark
7
A scientist is studying a new carbon compound. They find that it has a molecular formula of . They are trying to determine its possible structures.(a) Name the homologous series to which belongs. [1 mark](b) Draw the structures of at least two possible structural isomers for . [2 marks](c) Explain why can have structural isomers while propane () does not. 2marks
8
Assertion (A): Alcohols react with sodium metal to produce hydrogen gas.Reason (R): The hydrogen atom in the hydroxyl group (-OH) of alcohols is acidic and can be replaced by sodium.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
9
A student observes that while washing clothes with soap in tap water, a good lather is formed. However, when they try to wash clothes with the same soap in water from a mineral spring, it is difficult to form lather and a white precipitate is observed.(a) Why is it difficult to form lather with the soap in the water from the mineral spring? [2 marks](b) What is the white precipitate formed called, and what causes it? [1 mark](c) Suggest an alternative cleansing agent that would be effective even in the mineral spring water and explain why it works. 2marks
10
A food processing company wants to add a flavouring agent to their new range of ice creams. They are looking for a compound that is sweet-smelling and can be prepared by reacting an alcohol with a carboxylic acid in the presence of an acid catalyst.(a) Name the type of compound the company is looking for. [1 mark](b) Write a general word equation for the formation of this type of compound. [1 mark](c) Name the products formed when ethanol reacts with ethanoic acid in the presence of an acid catalyst. [1 mark](d) If this ester is treated with sodium hydroxide, what two products are formed? Name this reaction. 2marks
11
Assertion (A): Unsaturated hydrocarbons undergo addition reactions.Reason (R): Unsaturated hydrocarbons contain double or triple bonds between carbon atoms, which can break to form new single bonds.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
12
A farmer is using biogas as a fuel for cooking in their rural home. Biogas is primarily methane.(a) Write the chemical equation for the complete combustion of methane. [1 mark](b) Explain why biogas is considered a cleaner fuel compared to some other fossil fuels. [2 marks](c) If the farmer notices the bottom of their cooking vessel getting blackened, what does it indicate about the burning of the biogas? 2marks
13
A student is confused about the difference between saturated and unsaturated carbon compounds.(a) Define saturated carbon compounds. [1 mark](b) Define unsaturated carbon compounds. [1 mark](c) Give an example of a saturated hydrocarbon and an unsaturated hydrocarbon, along with their molecular formulae. [2 marks](d) Which type of hydrocarbon is more reactive and why? 1mark
14
Assertion (A): Carbon forms a large number of compounds because of its tetravalency and catenation.Reason (R): Carbon atoms can bond with four other atoms, and also with other carbon atoms to form long chains, branches, and rings.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
15
A scientist is investigating the properties of ethanoic acid. They want to perform a reaction to identify its acidic nature.(a) What observation would be made if ethanoic acid is reacted with sodium carbonate? Write the balanced chemical equation for this reaction. [2 marks](b) How would the observation differ if sodium chloride was reacted with ethanoic acid? Justify your answer. [2 marks](c) Name the salt formed when ethanoic acid reacts with sodium hydroxide. 1mark
16
A group of students is tasked with identifying an unknown organic compound. They are given that the compound is neutral to litmus, reacts with sodium metal to produce a gas that burns with a pop sound, and has two carbon atoms.(a) Identify the unknown compound. [1 mark](b) Write the chemical equation for the reaction of this compound with sodium metal. [1 mark](c) What is the role of concentrated sulphuric acid when this compound is heated with it at 443 K? Write the chemical equation for the reaction. [2 marks](d) Name the functional group present in this compound. 1mark
17
Assertion (A): Compounds like and form a homologous series.Reason (R): They have the same functional group (-OH) and successive members differ by a unit.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
18
A chef is preparing a dish using vegetable oil. The oil is described as being ‘healthy’ because it contains unsaturated fatty acids.(a) Explain the difference in terms of bonding between saturated and unsaturated fatty acids. [2 marks](b) What is the process called where vegetable oils are hydrogenated using a catalyst like nickel? [1 mark](c) Why is hydrogenation of vegetable oil considered beneficial for health compared to animal fats which are generally saturated? 2marks
19
A student is learning about soaps and detergents. They perform an experiment with hard water and soap solution.(a) What observation will the student make when soap solution is added to hard water? Explain the reason for this observation. [2 marks](b) How does a detergent differ from a soap in its effectiveness with hard water? Explain why. [2 marks](c) Name one common application of detergents other than cleaning clothes. 1mark
20
Assertion (A): Carbon compounds generally have low melting and boiling points.Reason (R): Carbon compounds form weak intermolecular forces between their molecules.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true. 1mark
Answers
1
(a) The physical properties of diamond and graphite differ because of their different crystal structures. In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement, forming a rigid, three-dimensional network. This strong, directional bonding makes diamond extremely hard. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane, forming hexagonal rings arranged in layers. The forces between these layers are weak (van der Waals forces), allowing the layers to slide over each other, making graphite soft and slippery.(b) In graphite, each carbon atom is bonded to three other carbon atoms, forming hexagonal rings. One of these bonds is a double bond, which means there is a delocalized electron (a free electron) for each carbon atom that is not involved in sigma bonding. These free electrons are mobile and can move throughout the layers of graphite, making it a good conductor of electricity.(c) Graphite is classified as a non-metal because its chemical properties are characteristic of non-metals, and it is primarily composed of carbon, which is a non-metal. Although it exhibits electrical conductivity, this is a property that some non-metals can possess (like silicon) and does not solely define a substance as metallic. Metals typically have other characteristics like malleability, ductility, and a tendency to form positive ions, which graphite does not exhibit.
2
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
3
(a) Petrol is a mixture of volatile hydrocarbons. When exposed to the atmosphere, these hydrocarbons absorb heat and undergo a phase transition from liquid to gas (vapour).(b) The products of complete combustion of hydrocarbons are carbon dioxide () and water ().(c) If the fuel is not burning completely due to insufficient air, the flame will be yellow and sooty. This is because incomplete combustion produces unburnt carbon particles (soot) along with carbon monoxide (CO) and water.
4
(a) In a methane molecule (), carbon has 4 valence electrons and each hydrogen has 1 valence electron. Carbon shares one electron with each of the four hydrogen atoms, and each hydrogen shares its electron with carbon. This results in the formation of four shared pairs of electrons.(b)
H | H - C - H | H Electron dot structure:H . H : C : H . H (c) In methane, carbon shares its 4 valence electrons with the 4 hydrogen atoms. Each hydrogen atom shares its 1 electron with carbon. This sharing results in carbon being surrounded by 8 electrons (its own 4 + 4 from hydrogen) and each hydrogen atom being surrounded by 2 electrons (its own 1 + 1 from carbon), thus achieving a noble gas configuration (octet for carbon, duplet for hydrogen).5
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
6
(a) When methane (a saturated hydrocarbon) burns in the presence of sufficient air, it produces a clean, blue flame. This is because methane undergoes complete combustion, producing mainly carbon dioxide and water, with minimal soot.(b) When ethene (an unsaturated hydrocarbon) burns in the presence of sufficient air, it produces a yellow, sooty flame. This is because unsaturated hydrocarbons tend to undergo incomplete combustion more readily, producing unburnt carbon particles (soot).(c) A deposition of black soot would be observed on the metal plate held over the burning ethene flame. This indicates the formation of unburnt carbon particles due to incomplete combustion.
7
(a) belongs to the homologous series of Alkanes.(b)Structure 1 (n-pentane): Structure 2 (isopentane/2-methylbutane):
CH3 | CH3 - CH - CH2 - CH3 Structure 3 (neopentane/2,2-dimethylpropane):CH3 | CH3 - C - CH3 | CH3 (c) Propane () has only three carbon atoms in a chain. It is not possible to arrange these three carbon atoms in a way that results in a different connectivity, thus it does not have structural isomers. However, with five carbon atoms, there are multiple ways to connect them (straight chain, branched chain), leading to different structural arrangements, hence structural isomers.8
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
9
(a) It is difficult to form lather with soap in the water from the mineral spring because this water is hard water, containing dissolved calcium and magnesium salts. These salts react with the soap (which is a sodium or potassium salt of a long-chain carboxylic acid) to form an insoluble precipitate called soap scum. This scum consumes the soap, making lather formation difficult.(b) The white precipitate formed is called soap scum. It is formed by the reaction of the sodium/potassium ions in the soap with the calcium/magnesium ions in the hard water, forming insoluble calcium/magnesium salts of the fatty acid.(c) A detergent would be an effective cleansing agent. Detergents are usually sodium salts of sulphonic acids or ammonium salts with long hydrocarbon chains. Their charged ends do not form insoluble precipitates with calcium and magnesium ions in hard water, so they remain effective and produce lather easily.
10
(a) The company is looking for an ester.(b) Alcohol + Carboxylic Acid Ester + Water(c) When ethanol reacts with ethanoic acid in the presence of an acid catalyst, the products formed are ethyl ethanoate (an ester) and water.(d) If ethyl ethanoate is treated with sodium hydroxide, it produces ethanol and sodium ethanoate. This reaction is called saponification.
11
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
12
(a) The chemical equation for the complete combustion of methane () is:
(b) Biogas is considered a cleaner fuel because its primary component, methane, produces mainly carbon dioxide and water upon complete combustion. This produces less air pollution (like sulphur dioxide or nitrogen oxides) compared to fossil fuels like coal or petroleum, which often contain impurities. (c) If the farmer notices the bottom of their cooking vessel getting blackened, it indicates that the biogas is not burning completely, i.e., incomplete combustion is occurring. This is likely due to insufficient supply of air.
13
(a) Saturated carbon compounds are those carbon compounds in which the carbon atoms are linked to each other by only single covalent bonds.
(b) Unsaturated carbon compounds are those carbon compounds in which there is at least one double or triple bond between carbon atoms.
(c) Example of a saturated hydrocarbon: Methane (), Ethane ().
Example of an unsaturated hydrocarbon: Ethene (), Ethyne ().
(d) Unsaturated hydrocarbons are more reactive because the double or triple bonds between carbon atoms can break more easily to form new single bonds with other atoms, allowing them to undergo addition reactions.
14
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
15
(a) When ethanoic acid reacts with sodium carbonate, effervescence (release of gas) will be observed. The gas produced will turn lime water milky.
Balanced chemical equation:
(b) If sodium chloride was reacted with ethanoic acid, there would be no significant visible reaction or gas evolution. This is because sodium chloride is a salt and does not react with a weak acid like ethanoic acid to produce a gas. Only reactions with carbonates and hydrogencarbonates produce carbon dioxide. (c) The salt formed when ethanoic acid reacts with sodium hydroxide is sodium ethanoate (or sodium acetate).
16
(a) The unknown compound is Ethanol (). It is neutral to litmus, reacts with sodium to produce hydrogen gas (which burns with a pop sound), and has two carbon atoms.
(b) Chemical equation for the reaction of ethanol with sodium metal:
(c) The role of concentrated sulphuric acid is that of a dehydrating agent. When ethanol is heated with excess concentrated sulphuric acid at 443 K, it undergoes dehydration to form ethene.
Chemical equation:
(d) The functional group present in ethanol is the hydroxyl group (-OH).
17
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
18
(a) Saturated fatty acids contain only single bonds between carbon atoms in their hydrocarbon chains. Unsaturated fatty acids contain one or more double or triple bonds between carbon atoms in their hydrocarbon chains.(b) The process is called hydrogenation.(c) Hydrogenation converts unsaturated fatty acids into saturated fatty acids. Animal fats, which are generally saturated, are said to be less healthy because they tend to raise cholesterol levels. Oils containing unsaturated fatty acids are considered healthier as they are more easily processed by the body.
19
(a) When soap solution is added to hard water, it will be difficult to form lather, and a white precipitate (scum) will be observed. This is because the calcium and magnesium ions present in hard water react with the soap molecules to form insoluble calcium and magnesium salts of the fatty acids, which form the scum and consume the soap.(b) Detergents are generally more effective in hard water than soaps because their charged ends do not form insoluble precipitates with the calcium and magnesium ions. Therefore, they continue to produce lather and clean effectively even in hard water.(c) Detergents are used in shampoos, dishwashing liquids, and laundry detergents for cleaning clothes and other surfaces.
20
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
