JAMB UTME - Chemistry - 2025

Crude oil (petroleum) is a complex mixture of hydrocarbons with different boiling points. To separate it into useful fractions (such as petrol/gasoline, kerosene, diesel, lubricating oil, and bitumen), fractional distillation is used.

In fractional distillation, crude oil is heated in a furnace until most of it vaporises. The vapour enters a tall fractionating column that is hot at the bottom and cool at the top. As the vapour rises through the column:

• Hydrocarbons with higher boiling points condense lower in the column (e.g., bitumen, heavy fuel oil).
• Hydrocarbons with lower boiling points rise higher before condensing (e.g., petrol, refinery gas).

The column contains trays at different heights where each fraction is collected.

The other separation methods are not suitable:

• Steam distillation is used for heat-sensitive compounds (like essential oils) that would decompose at their normal boiling points.
• Fractional crystallisation separates solids from solution based on differences in solubility at different temperatures.
• Precipitation is used to separate insoluble solids from a solution by adding a reagent.

A lone pair is a pair of valence electrons on an atom that is not shared in a bond. To find which molecule has the highest number of lone pairs, draw the Lewis structure of each molecule and count all lone pairs on every atom.

CH₄: Carbon has four bonding pairs (one to each hydrogen) and no lone pairs. Each hydrogen also has no lone pairs. Total lone pairs: 0.

NH₃: Nitrogen has three bonding pairs (one to each hydrogen) and one lone pair. Total lone pairs: 1.

H₂O: Oxygen has two bonding pairs (one to each hydrogen) and two lone pairs. Total lone pairs: 2.

CO₂: Carbon forms two double bonds (one to each oxygen) and has no lone pairs. Each oxygen in a double bond with carbon retains two lone pairs. Total lone pairs: 2 + 2 = 4.

CO₂ has the highest total number of lone pairs (four), making it the correct answer.

Exam tip: When counting lone pairs, remember to include those on every atom in the molecule, not just the central atom.

The number of molecules in a sample is found by multiplying the number of moles by Avogadro's number. The relationship is:

\[N = n \times N_A\]

where \(N\) is the number of molecules, \(n\) is the number of moles, and \(N_A\) is Avogadro's number (\(6.02 \times 10^{23}\)).

Substituting the given values:

\[N = 4.0 \times 6.02 \times 10^{23}\]

\[N = 24.08 \times 10^{23}\]

\[N = 2.408 \times 10^{24}\]

Rounding to three significant figures gives \(2.41 \times 10^{24}\) molecules.

A common error is dividing instead of multiplying. Dividing 6.02 by 4 would give \(1.51 \times 10^{23}\), which is the number of molecules in 0.25 moles, not 4.0 moles. When you have more than one mole, the number of molecules must be greater than Avogadro's number, so any answer smaller than \(6.02 \times 10^{23}\) can be immediately ruled out.

Tetraoxosulphate(VI) acid is the IUPAC name for sulphuric acid, \(\text{H}_2\text{SO}_4\). Its large-scale industrial manufacture uses the Contact process.

The Contact process involves three main stages:

1. Sulphur is burned in air to produce sulphur(IV) oxide: \(\text{S} + \text{O}_2 \rightarrow \text{SO}_2\)
2. Sulphur(IV) oxide is oxidised to sulphur(VI) oxide using a vanadium(V) oxide (\(\text{V}_2\text{O}_5\)) catalyst at about 450 \(^\circ\text{C}\): \(2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3\)
3. The \(\text{SO}_3\) is absorbed in concentrated \(\text{H}_2\text{SO}_4\) to form oleum (\(\text{H}_2\text{S}_2\text{O}_7\)), which is then carefully diluted with water to give concentrated sulphuric acid.

The other named processes serve different purposes. The Haber process manufactures ammonia from nitrogen and hydrogen. The Frasch process is used for mining sulphur deposits underground using superheated water. The Bosch process (or water-gas shift reaction) produces hydrogen from carbon monoxide and steam. None of these produces sulphuric acid.

Brine is a concentrated solution of sodium chloride (NaCl) in water. When brine is electrolysed using inert (neutral) electrodes such as carbon or platinum, the ions present in solution are:

• Cations: Na⁺ and H⁺ (from water)
• Anions: Cl^- and OH^- (from water)

At the anode (positive electrode), anions migrate and are discharged. Both Cl^- and OH^- are present, but Cl^- is preferentially discharged because it is present in much higher concentration in the brine solution. Despite OH^- having a lower discharge potential, the high concentration of Cl^- gives it priority at the anode.

The half-equation at the anode is:

\[2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-\]

Chlorine gas (Cl₂) is released at the anode.

Na⁺ and H⁺ are cations and migrate to the cathode, not the anode. At the cathode, H⁺ is discharged (since Na⁺ has a very high discharge potential), producing hydrogen gas.

In qualitative analysis, ions are classified as either acid radicals (anions) or basic radicals (cations).

• Acid radicals are the negative ions (anions) derived from acids. Examples include CO₃^2- (from H₂CO₃), SO₄^2- (from H₂SO₄), NO₃^- (from HNO₃), PO₄^3- (from H₃PO₄), and Cl^- (from HCl).
• Basic radicals are the positive ions (cations) derived from bases. Examples include Na⁺, K⁺, Mg²⁺, Ca²⁺, and Fe²⁺.

The question asks which group contains only acid radicals. Examining each option:

• CO₃^2-, PO₄^3-, Mg²⁺: contains Mg²⁺, which is a basic radical (cation).
• CO₃^2-, SO₄^2-, Na⁺: contains Na⁺, which is a basic radical (cation).
• CO₃^2-, SO₄^2-, NO₃^-: all three are anions derived from acids. This group contains only acid radicals.
• CO₃^2-, SO₄^2-, K⁺: contains K⁺, which is a basic radical (cation).

The correct answer is the group containing CO₃^2-, SO₄^2-, and NO₃^-, as all three are acid radicals.

The basicity of an acid is the number of replaceable hydrogen ions (\(\text{H}^+\)) that one molecule of the acid can donate in a reaction with a base.

The compound \(\text{C}_2\text{H}_2\text{O}_4\) is oxalic acid (also called ethanedioic acid). Its structural formula is:

\(\text{HOOC-COOH}\)

Oxalic acid contains two carboxyl groups (\(-\text{COOH}\)). Each carboxyl group carries one hydrogen atom that can be released as \(\text{H}^+\) during a neutralisation reaction. The remaining hydrogen atoms in the molecule are bonded to carbon and are not ionisable.

Since there are two replaceable hydrogen atoms, the basicity of oxalic acid is 2. This means it is a dibasic acid (also called a diprotic acid).

The neutralisation reaction with sodium hydroxide confirms this:

Two moles of NaOH are required to completely neutralise one mole of oxalic acid, confirming a basicity of 2.

When determining basicity, count only the hydrogen atoms bonded to oxygen in carboxyl or hydroxyl groups, not those bonded directly to carbon.

To name an organic compound using IUPAC nomenclature, follow these steps:

Step 1: Identify the structure. The compound is CH₃C≡CCH(CH₃)₂. Writing it out carbon by carbon:

• C-1: CH₃
• C-2: C (triple bond to C-3)
• C-3: C (triple bond to C-2)
• C-4: CH with two CH₃ groups attached

Step 2: Find the longest carbon chain containing the triple bond. The four carbons above give a chain of 4. However, one of the methyl groups on C-4 can extend the chain to 5 carbons: C-1, C-2, C-3, C-4, C-5 (incorporating one methyl into the main chain). The remaining methyl group on C-4 becomes a branch.

Step 3: Number the chain to give the triple bond the lowest possible locants. Numbering from the CH₃ end: the triple bond is at positions 2-3. This gives pent-2-yne.

Step 4: Name the substituent. The methyl branch is on C-4.

The complete IUPAC name is 4-methylpent-2-yne.

Choosing the right indicator for a titration depends on the strength of the acid and the base being used, because different indicators change colour at different pH ranges.

Ethanedioic acid (oxalic acid, HOOC-COOH) is a weak diprotic acid, and potassium hydroxide (KOH) is a strong base.

In a weak acid vs. strong base titration, the equivalence point lies in the basic/alkaline region (pH roughly 8-10). This is because at the equivalence point, the solution contains the conjugate base of the weak acid (potassium ethanedioate/oxalate), which hydrolyses to make the solution slightly basic.

Phenolphthalein changes colour in the pH range of approximately 8.2 to 10.0 (colourless in acid, pink in alkali). This range coincides with the equivalence point of a weak acid-strong base titration, making it the most suitable indicator.

Methyl orange (pH 3.1-4.4) and methyl red (pH 4.4-6.2) change colour in acidic pH ranges and would signal the endpoint too early, before the true equivalence point is reached. Methyl purple is less commonly used and is not the standard choice for this type of titration.

A blowing agent is a substance used to produce a cellular structure (foam) in materials such as plastics, rubber, and insulation. The term "blowing" refers specifically to the process of expanding a material by generating gas bubbles within it during manufacture.

Chlorofluorocarbons (CFCs) were widely used as blowing agents in the foam industry because they vaporise at low temperatures, creating uniform gas pockets that give foam products their lightweight, insulating structure. Expanded polystyrene, polyurethane foam, and similar products were traditionally manufactured using CFCs as the blowing agent.

While CFCs also have applications as refrigerants and aerosol propellants, those uses are distinct from the role of a blowing agent. A refrigerant absorbs and releases heat during phase changes in a cooling cycle, and a propellant provides pressure to expel contents from a container. Neither of these functions involves creating foam. The tyre industry does not use CFCs as blowing agents.

The key word in the question is "blowing agent," which points specifically to foam production.

The corrosion of iron is specifically called rusting. Rusting occurs when iron reacts with oxygen and water (moisture) over time to form hydrated iron(III) oxide, commonly known as rust:

\[4\text{Fe} + 3\text{O}_2 + 6\text{H}_2\text{O} \rightarrow 4\text{Fe(OH)}_3\]

The iron(III) hydroxide gradually dehydrates to form the familiar reddish-brown rust (Fe₂O₃ . xH₂O). Both oxygen and water must be present for rusting to occur; iron does not rust in dry air or in air-free water.

The other options are different processes entirely: burning (combustion) is a rapid reaction with oxygen involving flame and heat; galvanizing is a method of preventing corrosion by coating iron with a layer of zinc; alloying is mixing metals together to form an alloy (such as stainless steel), which is also a corrosion-prevention strategy, not a corrosion process.

Amines are classified based on the number of carbon-containing groups (alkyl or aryl groups) directly bonded to the nitrogen atom:

• Primary amine: nitrogen is bonded to one carbon group and two hydrogen atoms (R-NH₂).
• Secondary amine: nitrogen is bonded to two carbon groups and one hydrogen atom (R₂-NH).
• Tertiary amine: nitrogen is bonded to three carbon groups and no hydrogen atoms (R₃-N).

In CH₃CH(NH₂)CH₂CH₂CH₃, the nitrogen atom in the -NH₂ group is bonded to one carbon atom (the CH group in the chain) and two hydrogen atoms. This fits the definition of a primary amine.

The fact that the nitrogen is attached to a secondary carbon (a carbon bonded to two other carbons) does not change the amine classification. The classification depends only on how many carbons are bonded directly to nitrogen, not on the type of carbon.

Exam tip: Do not confuse amine classification (based on bonds to nitrogen) with alcohol classification (based on the type of carbon bearing the -OH group). A primary amine simply means nitrogen has one C-N bond.

The equation shows propane (\(C_3H_8\)) reacting with chlorine gas (\(Cl_2\)) in the presence of ultraviolet light to produce chloropropane (\(C_3H_7Cl\)) and hydrogen chloride (\(HCl\)).

In this reaction, a hydrogen atom on the propane molecule is replaced by a chlorine atom. This is the hallmark of a substitution reaction, specifically a free-radical substitution. The UV light provides the energy needed to break the \(Cl-Cl\) bond homolytically, generating chlorine free radicals that then attack the alkane.

It is not neutralization (no acid-base reaction), not polymerization (no repeating monomer units are joined), and not oxidation in the classical sense used here. The defining feature is the direct replacement of one atom (H) by another (Cl) in the organic molecule.

Concentrated sulphuric acid (H\(_2\)SO\(_4\)) has a very strong affinity for water. It is one of the most powerful dehydrating agents in chemistry, meaning it removes water (or the elements of water, H and O in a 2:1 ratio) from other substances.

This dehydrating ability is demonstrated in several ways:

• It chars sugar (sucrose, C\(_{12}\)H\(_{22}\)O\(_{11}\)) by removing water, leaving behind carbon.
• It is used in the laboratory to dry gases that do not react with it (e.g., drying chlorine, oxygen, or carbon dioxide).
• It dehydrates ethanol to produce ethene: \(\text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4} \text{C}_2\text{H}_4 + \text{H}_2\text{O}\)

The other options describe properties that are not characteristic of concentrated H\(_2\)SO\(_4\). Reacting with metals to produce hydrogen and neutralising alkalis are properties of dilute acids, not concentrated sulphuric acid specifically. Producing a cryolite precipitate is not a recognised reaction of sulphuric acid.

A water pollutant is any substance or condition that degrades the quality of a water body and harms aquatic life or makes the water unsuitable for its intended use.

Oxygen gas is not a water pollutant. In fact, dissolved oxygen is essential for aquatic life. Fish and other aquatic organisms depend on dissolved oxygen for respiration. A water body with adequate dissolved oxygen levels is considered healthy.

The other options are all recognised water pollutants:

• Warm water effluent (thermal pollution): Discharge of heated water from power plants or factories raises the temperature of natural water bodies, which reduces the solubility of dissolved oxygen and disrupts aquatic ecosystems.
• Inorganic fertilizers: Nitrates and phosphates from agricultural runoff cause eutrophication, leading to excessive algal growth, oxygen depletion, and death of aquatic organisms.
• Biodegradable waste: Organic matter such as sewage increases the biological oxygen demand (BOD) of the water, depleting dissolved oxygen as microorganisms decompose the waste.

Since oxygen gas is a natural and beneficial component of water, it is not classified as a pollutant.

The molecular mass (molar mass) of a substance is defined as the mass of one mole of that substance. The relationship is:

\[\text{Molar mass} = \frac{\text{Mass}}{\text{Number of moles}}\]

Given that 0.5 mole of the alkanoic acid weighs 44 g:

\[\text{Molar mass} = \frac{44\,\text{g}}{0.5\,\text{mol}} = 88\,\text{g/mol}\]

The molecular mass of the alkanoic acid is therefore 88. This corresponds to butanoic acid (CH₃CH₂CH₂COOH), which has the molecular formula C₄H₈O₂: (4 x 12) + (8 x 1) + (2 x 16) = 48 + 8 + 32 = 88.

A common error is to multiply mass by moles instead of dividing. Remember: if a fraction of a mole has a certain mass, the full mole must weigh proportionally more.

The fountain experiment demonstrates the very high solubility of certain gases in water. A round-bottom flask is filled with the gas and inverted over a trough of water (often containing an indicator). When a small amount of water enters the flask and dissolves the gas, the pressure inside drops dramatically. Atmospheric pressure then forces water up into the flask in a spectacular fountain.

For this experiment to work, the gas must be extremely soluble in water so that it dissolves almost instantly on contact, creating a near-vacuum inside the flask.

Hydrogen chloride (HCl) is the classic gas used. It is one of the most soluble gases in water: about 450 volumes of HCl dissolve in one volume of water at room temperature, forming hydrochloric acid. Ammonia (NH₃) is also commonly used for the same experiment, but it is not among the given options.

Hydrogen sulphide (H₂S) is only moderately soluble and is extremely toxic, making it unsuitable. Dinitrogen(I) oxide (N₂O, nitrous oxide) and nitrogen(II) oxide (NO, nitric oxide) are both poorly soluble in water and would not produce the dramatic pressure drop needed for the fountain effect.

Reforming is a petroleum refinery process that rearranges the molecular structure of hydrocarbons to produce higher-octane fuels and aromatic compounds. The most common type is catalytic reforming, which converts naphthenes (cycloalkanes) and straight-chain alkanes into aromatic hydrocarbons such as benzene, toluene, and xylene, typically using a platinum-based catalyst at high temperature.

The conversion of cyclohexane to benzene is a classic example of reforming. In this reaction, cyclohexane (C₆H₁₂) undergoes catalytic dehydrogenation, losing three molecules of hydrogen to form benzene (C₆H₆):

\[ \text{C}_6\text{H}_{12} \xrightarrow{\text{Pt catalyst, heat}} \text{C}_6\text{H}_6 + 3\text{H}_2 \]

This aromatization reaction increases the octane rating of the fuel fraction and produces valuable aromatic feedstocks for the chemical industry.

The other options describe different processes:

• Converting hexene to hexane is hydrogenation (addition of hydrogen across a double bond).
• Converting hexane to carbon(IV) oxide and water vapour is combustion (burning in oxygen).
• Converting hexane to butane and ethane is cracking (breaking larger molecules into smaller ones).

The empirical formula is the simplest whole-number ratio of atoms in a compound. The empirical formula mass (sometimes called empirical mass) is the molar mass corresponding to that simplest formula.

The molecular formula given is C₆H₁₂O₆. To find the empirical formula, divide all subscripts by their greatest common factor:

\[\text{GCF of } 6, 12, 6 = 6\]

\[\text{Empirical formula} = \text{C}_1\text{H}_2\text{O}_1 = \text{CH}_2\text{O}\]

Now calculate the empirical formula mass using the given atomic masses (H = 1, C = 12, O = 16):

\[\text{Empirical mass} = 12 + 2(1) + 16 = 30\]

As a check, the molecular mass of C₆H₁₂O₆ is 6(12) + 12(1) + 6(16) = 72 + 12 + 96 = 180. Dividing by the empirical mass: 180 / 30 = 6, confirming that the molecular formula is exactly 6 times the empirical formula.

When an inflated balloon is placed in a freezer, the temperature of the gas inside the balloon decreases. According to the kinetic molecular theory of gases, the average kinetic energy of gas molecules is directly proportional to absolute temperature:

\[\text{Average KE} = \tfrac{3}{2}kT\]

As temperature drops, the gas molecules move more slowly. Slower-moving molecules collide with the walls of the balloon less frequently and with less force, so they exert less pressure on the balloon walls. Since the balloon is flexible, it contracts until the internal and external pressures balance, causing the balloon to shrink.

The other options are incorrect:

• The volume does not increase - it decreases. This option contradicts what is observed.
• The number of gas molecules does not change. The balloon is sealed; no molecules escape or enter.
• Gas molecules never completely stop moving. According to kinetic theory, molecular motion only ceases at absolute zero (0 K), which is not reached in a domestic freezer.

This behaviour illustrates Charles's Law: at constant pressure, the volume of a gas is directly proportional to its absolute temperature (\(V \propto T\)).

In the electrolysis of concentrated sodium chloride solution (brine) using inert graphite electrodes, the products depend on the concentration of the solution and the electrode positions.

At the anode (positive electrode), negatively charged ions migrate and are discharged. In concentrated NaCl solution, both chloride ions (Cl^-) and hydroxide ions (OH^-) from water are present. However, because the chloride ion concentration is very high, chloride ions are preferentially discharged at the anode:

\[2\text{Cl}^{-}(aq) \rightarrow \text{Cl}_2(g) + 2e^{-}\]

This produces chlorine gas, which can be identified by its greenish-yellow colour and its ability to bleach damp litmus paper.

At the cathode, hydrogen gas is produced from the reduction of water (since Na⁺ ions are too electropositive to be discharged). Oxygen gas would be the anode product only in the electrolysis of dilute sodium chloride or dilute sulphuric acid, where hydroxide ions are discharged instead of chloride ions. Water vapour and hydrogen gas are not anode products in this process.

The electron configuration 1s² 2s² 2p⁶ 3s² 3p⁵ has a total of 2 + 2 + 6 + 2 + 5 = 17 electrons, which identifies the element as chlorine (Cl, atomic number 17).

The group number of an element in the periodic table is determined by the number of electrons in its outermost (valence) shell. For chlorine, the outermost shell is the third shell (n = 3), which contains:

\[3s^2\,3p^5 = 2 + 5 = 7 \text{ electrons}\]

Therefore, chlorine belongs to Group 7 (also called Group VII or Group 17 in modern IUPAC numbering). Group 7 elements are the halogens: fluorine, chlorine, bromine, iodine, and astatine. They all have seven electrons in their outermost shell, giving them the general outer-shell configuration ns² np⁵.

Water has an unusually high boiling point (100 °C) for a molecule of its small size (relative molecular mass = 18). To understand why, compare water (H₂O) with hydrogen sulphide (H₂S), which has a larger relative molecular mass of 34 but is a gas at room temperature (boiling point -60 °C). The difference lies in the type of intermolecular forces present.

Each water molecule can form up to four hydrogen bonds with neighbouring molecules. Oxygen is highly electronegative, creating a large partial positive charge on the hydrogen atoms. These hydrogen atoms are attracted to the lone pairs on the oxygen of adjacent water molecules, forming strong intermolecular hydrogen bonds. This extensive hydrogen-bonding network requires a large amount of energy to break, which raises the boiling point far above what the molecular mass alone would predict.

The covalent bonds within each water molecule (O-H bonds) hold the atoms together inside one molecule, but they do not determine the physical state. Van der Waals forces are present in all molecules but are too weak on their own to keep such a light molecule in the liquid state at room temperature. Electrovalent (ionic) bonds do not exist in water, which is a covalent molecular substance.

It is therefore the strong hydrogen bonding between water molecules that keeps water liquid at room temperature.

To name this compound using IUPAC nomenclature, first expand the condensed structural formula (CH\(_3\))\(_2\)CHCH(OH)CH\(_2\)C(CH\(_3\))\(_3\):

\[\text{CH}_3-\underset{|}{\overset{\text{CH}_3}{\text{CH}}}-\underset{|}{\overset{\text{OH}}{\text{CH}}}-\text{CH}_2-\underset{|}{\overset{\text{CH}_3}{\underset{|}{\overset{}{\text{C}}}}}(\text{CH}_3)_2\]

Step 1: Find the longest carbon chain containing the OH group.

Tracing through the backbone: CH\(_3\)-CH-CH(OH)-CH\(_2\)-C-CH\(_3\) gives 6 carbons, so the parent chain is hexane.

Step 2: Number to give the OH group the lowest locant.

Numbering from the end nearest the OH group:

• C1: CH\(_3\) (end near the isopropyl group)
• C2: CH (bearing one CH\(_3\) branch)
• C3: CH-OH
• C4: CH\(_2\)
• C5: C (bearing two CH\(_3\) branches)
• C6: CH\(_3\)

OH is on carbon 3. Numbering from the other end would place OH on carbon 4, which is higher, so this direction is correct.

Step 3: Identify substituents.

• Carbon 2: one methyl group
• Carbon 5: two methyl groups

There are three methyl substituents at positions 2, 5, and 5.

Step 4: Construct the name.

The IUPAC name is 2,5,5-trimethylhexan-3-ol.

The table lists five organic compounds by their general formulae:

Compound V has the formula RCOOR', which is the general formula for an ester. Esters are produced through a reaction called esterification, in which a carboxylic acid reacts with an alcohol in the presence of a concentrated acid catalyst (typically concentrated \(\text{H}_2\text{SO}_4\)).

The reaction is:

From the table, compound IV (RCOOH) is a carboxylic acid and compound I (ROH) is an alcohol. When these two react together in the presence of an acid catalyst, they undergo a condensation reaction, releasing water and forming the ester RCOOR', which is compound V.

The other pairings do not produce an ester. A ketone (RCOR') lacks the hydroxyl group needed for esterification. An ether (ROR') is relatively unreactive under these conditions and does not participate in ester formation. Only the combination of a carboxylic acid and an alcohol yields an ester through acid-catalyzed condensation.

The correct pair is therefore I and IV.

Exam tip: whenever you see RCOOR' or are asked about ester formation, recall that it always requires a carboxylic acid (-COOH) and an alcohol (-OH) with an acid catalyst, and that water is released as a by-product.

This is a Faraday's law of electrolysis problem. The relationship between mass deposited, current, and time is:

\[m = \frac{M \times I \times t}{n \times F}\]

where \(m\) = mass deposited (g), \(M\) = molar mass, \(I\) = current (A), \(t\) = time (s), \(n\) = number of electrons transferred per ion, and \(F\) = Faraday constant (96500 C/mol).

For aluminium: \(\text{Al}^{3+} + 3e^- \rightarrow \text{Al}\), so \(n = 3\), \(M = 27\), \(m = 9\) g, \(I = 18\) A.

Rearranging for time:

\[t = \frac{m \times n \times F}{M \times I}\]

\[t = \frac{9 \times 3 \times 96500}{27 \times 18}\]

\[t = \frac{2\,605\,500}{486}\]

\[t = 5360.49 \text{ seconds}\]

Converting to minutes:

\[t = \frac{5360.49}{60} = 89.34 \text{ minutes}\]

The time required is 89.34 minutes.

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. It occurs in gases, liquids, and solids, though it is slowest in solids because the particles are closely packed and vibrate in fixed positions.

When a gold bar and a silver bar are pressed firmly together and left for years, gold atoms gradually migrate into the silver bar (and vice versa). This happens because the metal atoms, though fixed in a lattice, vibrate continuously. Over very long periods, some atoms acquire enough energy to move into neighbouring lattice positions, slowly spreading through the other metal. This is solid-state diffusion.

Brownian movement describes the random, erratic motion of microscopic particles suspended in a fluid (liquid or gas) caused by collisions with the surrounding fluid molecules. It does not apply to atoms within a solid lattice. Displacement is a chemical reaction in which a more reactive element replaces a less reactive one in a compound. Osmosis is the movement of water molecules through a semipermeable membrane from a dilute to a concentrated solution. Neither of these describes the mixing of atoms between two solid metals in contact.

Benzene (\(\text{C}_6\text{H}_6\)) is a cyclic aromatic hydrocarbon with a six-membered ring containing three alternating double bonds (or, more precisely, delocalised electrons). When benzene undergoes catalytic hydrogenation, three molecules of hydrogen add across the ring, saturating all the double bonds while preserving the ring structure:

\[\text{C}_6\text{H}_6 + 3\text{H}_2 \xrightarrow{\text{Ni, heat/pressure}} \text{C}_6\text{H}_{12}\]

The product is cyclohexane, a six-membered saturated ring. The key point is that hydrogenation adds hydrogen to the double bonds but does not break open the ring. Hexane (\(\text{C}_6\text{H}_{14}\)) is a straight-chain alkane, which would require ring-opening and further hydrogen addition; that is not what happens here.

Margarine is produced by the catalytic hydrogenation of unsaturated vegetable oils (fats), not benzene. Hexene is an unsaturated six-carbon compound that would result from incomplete hydrogenation of a different starting material, not from benzene.

Permalloy is an alloy composed of iron (Fe) and nickel (Ni), typically in a ratio of approximately 20% iron and 80% nickel, though the exact composition can vary.

Permalloy is valued for its exceptionally high magnetic permeability, meaning it is very easily magnetised even by weak magnetic fields. This property makes it useful in:

• Transformer cores
• Magnetic shielding
• Recording heads in data storage devices
• Sensitive magnetic instruments

The other metals listed form different alloys with iron:

• Iron + tin = tin plate (tin-coated iron, used for food cans)
• Iron + chromium (plus nickel and carbon) = stainless steel
• Iron + copper is not a standard named alloy

The defining feature of permalloy is that it is a nickel-iron alloy.

The compound [Cu(NH₃)₄]Cl₂ consists of two distinct parts:

• The complex cation: [Cu(NH₃)₄]²⁺ (copper(II) tetraamine ion)
• The anions: 2 Cl^- (chloride ions)

The question asks about the bond between the complex cation and the chloride ions. The complex cation carries a 2+ charge, and each chloride ion carries a 1- charge. The attraction between these oppositely charged ions is an ionic bond (electrostatic attraction).

It is important to distinguish this from the bonding within the complex ion. Inside [Cu(NH₃)₄]²⁺, each NH₃ molecule donates a lone pair of electrons from nitrogen to the Cu²⁺ ion, forming dative (coordinate) bonds. However, the question specifically asks about the bond between the complex and chlorine, which is ionic.

The spontaneity of a reaction is determined by the Gibbs free energy change, given by:

\[\Delta G = \Delta H - T\Delta S\]

A reaction is spontaneous when \(\Delta G\) is negative.

In this question:

• \(\Delta H\) is positive and small (slightly endothermic).
• \(\Delta S\) is positive and large (significant increase in disorder).

Substituting into the equation:

\[\Delta G = (\text{small positive}) - T \times (\text{large positive})\]

Since \(T\) (absolute temperature in Kelvin) is always positive, the term \(T\Delta S\) will be a large positive number. Subtracting this large positive value from a small positive \(\Delta H\) gives:

\[\Delta G = \text{small positive} - \text{large positive} = \text{negative}\]

A negative \(\Delta G\) means the reaction is spontaneous.

Exam tip: When \(\Delta H\) is positive but \(\Delta S\) is also positive and large, the entropy term dominates, and the reaction is spontaneous, especially at higher temperatures. This is called an entropy-driven reaction.

An alkaline gas is a gas that dissolves in water to produce a solution with a pH greater than 7 (a basic solution).

NH₃ (ammonia) is the classic example. When ammonia dissolves in water, it reacts to form ammonium hydroxide:

\[\text{NH}_3(g) + \text{H}_2\text{O}(l) \rightleftharpoons \text{NH}_4^+(aq) + \text{OH}^-(aq)\]

The production of hydroxide ions (OH^-) makes the solution alkaline.

The other gases are not alkaline:

• HCl (hydrogen chloride) dissolves in water to form hydrochloric acid, which is strongly acidic.
• N₂ (nitrogen) is an inert, unreactive gas that does not dissolve appreciably in water and produces neither acidic nor basic solutions.
• NO₂ (nitrogen dioxide) dissolves in water to form a mixture of nitric acid and nitrous acid, both of which are acidic.

Exam tip: Ammonia is the only common alkaline gas encountered at this level. Its characteristic pungent smell and ability to turn moist red litmus paper blue are standard identification tests.

Oxidation and reduction are defined in terms of electron transfer:

• Oxidation is the loss (removal) of electrons from a species.
• Reduction is the gain (addition) of electrons to a species.

A useful mnemonic is OIL RIG: Oxidation Is Loss, Reduction Is Gain.

For example, when iron is oxidised:

\[\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^-\]

Iron loses two electrons, so its oxidation state increases from 0 to +2. The electrons are removed from the iron atom.

The other options are incorrect: "added" describes reduction (the opposite process), while "hydrolysed" (broken down by water) and "hydrated" (combined with water molecules) are unrelated to the electron-transfer definition of oxidation.

Magnesium tetraoxosulphate(VI) is the systematic name for magnesium sulphate (MgSO\(_4\)). In its hydrated form, MgSO\(_4\)\(\cdot\)7H\(_2\)O, it is commonly known as Epsom salt.

Epsom salt is widely used in medicine as a laxative. When taken orally, magnesium sulphate draws water into the intestines by osmosis (it is poorly absorbed), which softens the stool and stimulates bowel movement. This makes it an effective saline laxative.

The other options do not match:

• A disinfectant kills microorganisms - examples include sodium hypochlorite or phenol, not MgSO\(_4\).
• A plasticizer is added to polymers to increase flexibility - these are typically organic esters such as dioctyl phthalate.
• While magnesium and sulphur are plant nutrients, MgSO\(_4\) is not the standard compound referred to as a fertilizer at examination level. Its primary and best-known use is as a laxative.

The structural formula shows H₃C-CH₂-C(=O)-O-CH₂-CH₃, which is an ester. To name an ester using IUPAC nomenclature, identify two parts:

The acid component (to the left of the ester linkage -C(=O)-O-): There are three carbon atoms (CH₃-CH₂-C=O), which corresponds to propanoic acid. In the ester name, this becomes propanoate.

The alkyl component (to the right of the ester oxygen): There are two carbon atoms (-O-CH₂-CH₃), which is an ethyl group.

Combining both parts, the ester is named ethyl propanoate. The alkyl group name comes first, followed by the name derived from the parent carboxylic acid with the -ic acid suffix replaced by -ate.

The energy profile diagram shows the energy changes during a chemical reaction. The reactants (A+B) start at an energy level of approximately 30 units, while the products (C+D) end at approximately 50 units. The activation energy peak reaches about 80 units.

Since the products have a higher energy level than the reactants, the reaction has absorbed energy from the surroundings. This net gain in energy by the reacting system is the defining characteristic of an endothermic reaction. The energy difference between products and reactants (\ (\Delta H\)) is positive, confirming that heat was taken in rather than released.

An exothermic reaction would show products at a lower energy level than reactants, indicating a release of energy. Here, the upward shift from reactants to products clearly indicates energy absorption.

Freons are a group of chlorofluorocarbons (CFCs) - synthetic compounds containing chlorine, fluorine, and carbon. They were widely used as propellants in aerosol cans, as refrigerants in air conditioners and refrigerators, and as solvents in industrial cleaning.

When released into the atmosphere from these sources, freons rise to the stratosphere where ultraviolet radiation breaks them down, releasing chlorine atoms. These chlorine atoms catalytically destroy ozone molecules, contributing to the depletion of the ozone layer.

Fossil fuel combustion releases carbon dioxide, sulphur dioxide, and nitrogen oxides, but not freons. Photosynthesis is a biological process that produces oxygen and consumes carbon dioxide. Organic decay releases methane and carbon dioxide. None of these processes involve freons.

The Montreal Protocol (1987) restricted the production and use of CFCs, leading to a gradual recovery of the ozone layer.

The expression shown is V \(\propto\) nT/P. This can be derived from the ideal gas equation PV = nRT, which rearranges to V = nRT/P. Since R is a constant, V is directly proportional to nT/P.

This expression combines three individual gas laws into one:

• Boyle's law: V \(\propto\) 1/P (at constant n and T)
• Charles' law: V \(\propto\) T (at constant n and P)
• Avogadro's law: V \(\propto\) n (at constant T and P)

Because the expression accounts for changes in all three variables (amount of substance n, temperature T, and pressure P) simultaneously, it represents the general gas law, not any single individual law.

Brine is a concentrated solution of sodium chloride (NaCl) in water. During electrolysis of brine, the ions present are Na⁺, Cl^-, H⁺ (from water), and OH^- (from water).

At the cathode (negative electrode), reduction takes place. The two cations competing for discharge are Na⁺ and H⁺. Because hydrogen ions are much easier to reduce than sodium ions (sodium has a very negative standard electrode potential), H⁺ ions are preferentially discharged:

\[2\text{H}^+(aq) + 2e^- \rightarrow \text{H}_2(g)\]

The gas produced at the cathode is therefore hydrogen.

At the anode (positive electrode), chloride ions are oxidised to produce chlorine gas. Sodium hydroxide remains in solution. Steam is not produced during electrolysis, and oxygen would only appear at the anode if a dilute solution were used instead of concentrated brine.

Exam tip: In electrolysis of brine, remember the three products: hydrogen at the cathode, chlorine at the anode, and sodium hydroxide in solution.

Colloids are classified based on the physical states of the dispersed phase (the substance spread throughout) and the dispersion medium (the substance in which it is spread). The main types include:

A commercial deodorant spray works by dispersing tiny liquid droplets (the fragrance and active ingredients) into the air (a gas). This makes it an aerosol - a colloid in which a liquid is dispersed in a gas.

It is not a foam (gas in liquid/solid), not an emulsion (liquid in liquid), and not a sol (solid in liquid).