JAMB UTME - Chemistry - 2025

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When solid particles such as dust and sand are dispersed in a gas (air), the resulting system is classified based on particle size and behaviour.

A suspension is a heterogeneous mixture in which relatively large, visible particles are dispersed in a medium. The particles in a suspension are large enough to eventually settle out under gravity and can often be seen with the naked eye. Dust and sand particles in air fit this description: they are large, they scatter light visibly, and they settle when the air is still.

The other options do not fit:

• An emulsion is a mixture of two immiscible liquids (such as oil in water). Dust in air does not involve two liquids.
• A saturated solution is a homogeneous mixture where no more solute can dissolve at a given temperature. Dust particles are not dissolved in air.
• A dispersion is a broad term for any system in which one substance is spread throughout another, but it does not specifically describe the large-particle, settling behaviour of dust and sand in air.

Because dust and sand particles are large, visible, and settle out over time, the system is best classified as a suspension.

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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.

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Anti-freeze is a substance added to the water in a vehicle's radiator to lower its freezing point, preventing the coolant from solidifying in cold weather and potentially cracking the engine block.

Among the options given, propanetriol (glycerol or propane-1,2,3-triol, HOCH\(_2\)CH(OH)CH\(_2\)OH) has historically been used as an anti-freeze. Glycerol is highly soluble in water in all proportions, and when dissolved, it significantly depresses the freezing point of the mixture. This is a colligative property: the dissolved solute particles disrupt the formation of ice crystals, requiring a lower temperature to freeze.

The other options are unsuitable:

• Propanol (CH\(_3\)CH\(_2\)CH\(_2\)OH) is a flammable alcohol not used in radiator systems.
• Propanone (acetone, CH\(_3\)COCH\(_3\)) is a volatile ketone and a solvent, not an anti-freeze.
• Propanal (CH\(_3\)CH\(_2\)CHO) is an aldehyde with no anti-freeze application.

In modern practice, ethylene glycol (ethane-1,2-diol) is more commonly used, but among the four choices provided, propanetriol is the correct answer.

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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.

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Sulphuric acid (H₂SO₄) is a diprotic acid, meaning each molecule donates two hydrogen ions when it dissociates completely in water:

\[\text{H}_2\text{SO}_4(aq) \rightarrow 2\text{H}^+(aq) + \text{SO}_4^{2-}(aq)\]

Step 1: Find [H⁺]

Since each mole of H₂SO₄ produces 2 moles of H⁺:

\[[\text{H}^+] = 2 \times 0.06 = 0.12 \text{ mol dm}^{-3} = 1.2 \times 10^{-1} \text{ mol dm}^{-3}\]

Step 2: Find [OH^-]

Using the ionic product of water at 25 °C:

\[K_w = [\text{H}^+][\text{OH}^-] = 1.0 \times 10^{-14}\]

\[[\text{OH}^-] = \frac{K_w}{[\text{H}^+]} = \frac{1.0 \times 10^{-14}}{1.2 \times 10^{-1}}\]

\[[\text{OH}^-] = \frac{1.0}{1.2} \times 10^{-14+1} = 0.833 \times 10^{-13} = 8.3 \times 10^{-14} \text{ mol dm}^{-3}\]

Therefore [H⁺] = \(1.2 \times 10^{-1}\) mol dm^-3 and [OH^-] = \(8.3 \times 10^{-14}\) mol dm^-3.

A common mistake is forgetting that sulphuric acid is diprotic and using [H⁺] = 0.06 instead of 0.12, which would give \(1.2 \times 10^{-2}\) instead of \(1.2 \times 10^{-1}\) and an incorrect OH^- concentration of \(8.3 \times 10^{-13}\).

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The homologous series of alkenes are unsaturated hydrocarbons that contain exactly one carbon-carbon double bond (C=C). Their general molecular formula is \(\text{C}_n\text{H}_{2n}\), where n is the number of carbon atoms (n >= 2).

To verify, consider a few members:

• Ethene (n = 2): C₂H₄ = C₂H₂₍₂₎
• Propene (n = 3): C₃H₆ = C₃H₂₍₃₎
• Butene (n = 4): C₄H₈ = C₄H₂₍₄₎

Each formula fits \(\text{C}_n\text{H}_{2n}\).

The other general formulae belong to different homologous series: \(\text{C}_n\text{H}_{2n+2}\) represents alkanes (saturated hydrocarbons), \(\text{C}_n\text{H}_{2n-2}\) represents alkynes (with a triple bond), and \(\text{C}_n\text{H}_{2n+1}\text{OH}\) represents alkanols (alcohols).

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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.

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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.

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Gold is one of the least reactive metals, sitting at the very bottom of the reactivity series. Because of this extremely low reactivity, gold does not combine with other elements under natural conditions. It therefore occurs in the earth's crust as the free (uncombined) metal, often found as nuggets or flakes in alluvial deposits.

Since gold already exists in its elemental form, there is no need for chemical extraction from an ore. Metals higher in the reactivity series (such as iron, aluminium, or sodium) form stable compounds with oxygen, sulphur, or other elements and must be chemically reduced to obtain the pure metal. Gold does not form such compounds naturally, so it is simply recovered by physical methods like panning or washing.

The phrase free in nature specifically means the metal is found uncombined. While gold is indeed unreactive (inert), the reason it does not require extraction is that it occurs free in nature, which is the more precise and direct answer to the question. Being "inert" describes a property; being "free in nature" describes the consequence of that property that directly answers why extraction is unnecessary.

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Esters (alkanoates) are the class of organic compounds responsible for the pleasant, fruity scents found in many fruits and perfumes. Esters are formed by the condensation reaction between an alkanol (alcohol) and an alkanoic acid (carboxylic acid) in the presence of a concentrated acid catalyst:

\[\text{Alkanoic acid} + \text{Alkanol} \xrightarrow{\text{H}^+} \text{Alkanoate (ester)} + \text{H}_2\text{O}\]

For example, ethyl ethanoate (CH\(_3\)COOC\(_2\)H\(_5\)) has a fruity smell resembling nail polish or pear drops. Different combinations of acids and alcohols produce esters with distinct aromas - banana, pineapple, apple, and many others.

The other options are different functional group classes with different characteristic properties:

• Alkanamides (amides, R-CO-NH\(_2\)) are generally odourless solids.
• Alkanones (ketones, R-CO-R') have sharp, often solvent-like odours - not fruity.
• Alkanals (aldehydes, R-CHO) tend to have pungent, irritating smells at low molecular weight.

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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.

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Aluminium (Al) is the metal widely used as a packaging material. It is used to make drink cans, food containers, and aluminium foil for wrapping food.

Aluminium is ideal for packaging because of several key properties:

• Low density - it is lightweight, making it easy to transport and handle.
• Malleability - it can be rolled into very thin sheets (foil) or pressed into various container shapes.
• Corrosion resistance - it forms a tough, protective oxide layer (\(\text{Al}_2\text{O}_3\)) on its surface that prevents further reaction with air or moisture, keeping the contents safe.
• Non-toxicity - it does not contaminate food or beverages.
• Recyclability - aluminium can be recycled repeatedly without losing its properties.

The other metals are unsuitable for packaging:

• Copper (Cu) is too heavy and expensive for everyday packaging, and it can impart a metallic taste to food.
• Iron (Fe) rusts readily when exposed to moisture and air, which would contaminate and spoil packaged goods.
• Sodium (Na) is an extremely reactive alkali metal that reacts violently with water and catches fire in air, making it entirely impractical for packaging.

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The compound CH₃-CH₂-COOCH₂-CH₃ contains the ester functional group (-COO-). To identify the reactants that formed this ester, split the structure at the ester linkage (between the carbonyl carbon and the oxygen bonded to the alkyl group).

The ester bond in -COO- comes from two parts:

• The acid part (to the left of -COO-): CH₃-CH₂-COO-. This corresponds to the carboxylate portion of propanoic acid (CH₃CH₂COOH), a three-carbon carboxylic acid.
• The alcohol part (to the right of -COO-): -CH₂-CH₃. This corresponds to the alkyl group from ethanol (CH₃CH₂OH), a two-carbon alcohol.

The ester is therefore ethyl propanoate, formed from propanoic acid and ethanol:

\[\text{CH}_3\text{CH}_2\text{COOH} + \text{CH}_3\text{CH}_2\text{OH} \rightleftharpoons \text{CH}_3\text{CH}_2\text{COOCH}_2\text{CH}_3 + \text{H}_2\text{O}\]

The correct reactants are propanoic acid and ethanol.

Exam tip: To identify the parent acid and alcohol of an ester, break the molecule at the single-bond oxygen in the -COO- group. The fragment bonded to the carbonyl (C=O) gives the acid; the fragment bonded through the oxygen gives the alcohol.

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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.

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Carbon(II) oxide is the IUPAC-style name for carbon monoxide (CO). It is a colourless, odourless, and highly toxic gas that is a major air pollutant, especially in urban areas.

The primary source of carbon monoxide as an air pollutant is the incomplete combustion of carbon-containing fuels. When fuels such as petrol, diesel, kerosene, coal, or wood burn with an insufficient supply of oxygen, carbon is only partially oxidised to CO instead of fully oxidised to CO₂:

\[ 2\text{C} + \text{O}_2 \rightarrow 2\text{CO} \]

Vehicle exhaust emissions are the single largest contributor of CO to the atmosphere, along with industrial furnaces and domestic cooking fires that operate under oxygen-poor conditions.

Respiration produces carbon dioxide (CO₂), not carbon monoxide. Photochemical smog is a secondary pollution phenomenon caused by sunlight acting on nitrogen oxides and volatile organic compounds; it is not a source of CO itself. Decomposition of sewage releases gases such as methane (CH₄) and hydrogen sulphide (H₂S), not carbon monoxide.

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KOH is a strong base that dissociates completely in water:

\[\text{KOH} \rightarrow \text{K}^+ + \text{OH}^-\]

For a 0.001 M KOH solution, the concentration of hydroxide ions is:

\[[\text{OH}^-] = 0.001\;\text{M} = 10^{-3}\;\text{M}\]

First, calculate the pOH:

\[\text{pOH} = -\log[\text{OH}^-] = -\log(10^{-3}) = 3\]

Then, use the relationship between pH and pOH at 25 \(^\circ\)C:

\[\text{pH} + \text{pOH} = 14\]

\[\text{pH} = 14 - 3 = 11\]

The pH of 0.001 M KOH solution is 11.

Exam tip: For strong bases, first find [OH^-] from the molarity, calculate pOH, then subtract from 14 to get pH. A pH of 11 confirms a basic solution, which is consistent with KOH being a strong alkali.

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A physical change is a change in which no new substance is formed. The original substance can be recovered by simple physical methods (such as evaporation, filtration, or condensation), and no chemical bonds are broken or formed between different types of atoms.

Dissolving sodium chloride in water is a physical change. When NaCl dissolves, the ionic lattice breaks apart and Na⁺ and Cl^- ions become surrounded by water molecules (hydration). However, no new chemical substance is created. The sodium chloride can be fully recovered by evaporating the water. The process is reversible.

The other options all involve chemical changes:

• Addition of water to calcium oxide: CaO + H₂O → Ca(OH)₂. A new substance (calcium hydroxide) is formed, and considerable heat is released.
• Corrosion of iron: Iron reacts with oxygen and moisture to form iron(III) oxide (rust, Fe₂O₃). New substances are produced irreversibly.
• Burning of charcoal: C + O₂ → CO₂. Combustion produces a completely different substance (carbon dioxide) and is irreversible.

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Chlorine has an atomic number of 17, meaning a neutral chlorine atom has 17 electrons. These electrons fill the available subshells in order of increasing energy:

1. \(1s\) holds 2 electrons (total: 2)
2. \(2s\) holds 2 electrons (total: 4)
3. \(2p\) holds 6 electrons (total: 10)
4. \(3s\) holds 2 electrons (total: 12)
5. \(3p\) holds the remaining 5 electrons (total: 17)

The electron configuration is therefore: \(1s^2\,2s^2\,2p^6\,3s^2\,3p^5\)

Examining the other options:

• \(1s^2\,2s^2\,2p^6\,3s^2\,3p^4\) gives only 16 electrons (this is sulphur).
• \(1s^2\,2s^2\,2p^6\,3s^2\,3p^6\) gives 18 electrons (this is argon).
• \(1s^2\,2s^2\,2p^5\,3s^2\,3p^6\) gives 17 electrons but violates the aufbau principle - the \(2p\) subshell must fill completely (6 electrons) before the \(3s\) subshell begins.

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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.

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This question tests the ability to read and interpret a solubility-temperature graph. The graph plots solubility (y-axis) against temperature in °C (x-axis) for four substances: X, Y, Z, and Q.

Examining each curve on the graph:

• X shows a steep, curved increase in solubility with temperature. Its solubility rises slowly at lower temperatures but accelerates sharply at higher temperatures, giving a concave-upward curve.
• Y follows a straight line from the origin, rising at a constant rate as temperature increases. This is a steady, linear increase in solubility.
• Z appears as a nearly horizontal line at about 45 units of solubility, meaning its solubility barely changes regardless of temperature. Z is essentially temperature-independent.
• Q rises to a peak around 40 to 50 °C and then decreases, meaning its solubility first increases and then drops with further heating.

The correct inference is that the solubility of Y increases steadily as temperature increases. The word "steadily" is key here: Y's straight-line graph means its solubility rises at a uniform, constant rate per degree of temperature increase. X also increases with temperature, but its increase is not steady; it accelerates (curves upward), so the rate of increase itself changes.

The claim that the solubility of X and Y is the same at all temperatures is incorrect because the two curves only intersect at a single point; at all other temperatures, their solubilities differ. The claim that the solubility of X, Y, and Z is temperature dependent is incorrect because Z is nearly flat, showing its solubility is essentially independent of temperature. The claim that the solubility of Z increases as temperature increases is directly contradicted by Z's horizontal line on the graph.

Exam tip: When a question uses the word "steadily," look for a straight-line relationship on the graph. A curve that bends upward or downward represents a changing rate of increase, not a steady one.

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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.

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When air is passed through a series of reagents, each one absorbs a specific component:

1. Alkaline pyrogalol (alkaline solution of pyrogallol) absorbs oxygen (O₂). Pyrogallol in alkaline solution reacts readily with oxygen and turns dark brown.
2. Potash (concentrated potassium hydroxide solution, KOH) absorbs carbon dioxide (CO₂). The CO₂ reacts with KOH to form potassium carbonate: CO₂ + 2KOH → K₂CO₃ + H₂O.
3. Fused calcium chloride (CaCl₂) in a U-tube absorbs water vapour (H₂O). Anhydrous CaCl₂ is a powerful desiccant (drying agent).

The main components of air are nitrogen (~78%), oxygen (~21%), argon and other noble gases (~0.9%), carbon dioxide (~0.04%), and water vapour (variable). After removing oxygen, carbon dioxide, and water vapour, the components that remain unabsorbed are noble gases and nitrogen. These are chemically inert (noble gases) or unreactive with the reagents used (nitrogen), so none of the three reagents can remove them.

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In the nitrogen cycle, when organisms die, their proteins and other nitrogenous compounds are broken down by decomposing bacteria in a process called ammonification (or decay). The first product of this decomposition is ammonia (NH₃).

The process occurs in stages:

1. Proteins in dead material are broken down into amino acids by proteolytic enzymes from decomposing bacteria and fungi.
2. The amino acids are further deaminated (the amino group -NH₂ is removed), releasing ammonia (NH₃).

After ammonia is produced, nitrifying bacteria can convert it further: first to nitrites (dioxonitrate(III), NO₂^-) by Nitrosomonas, then to nitrates (trioxonitrate(V), NO₃^-) by Nitrobacter. However, the question asks specifically about the first conversion product of nitrogenous compounds in dead materials, which is ammonia.

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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).

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The melting and boiling points of a substance depend on the strength of the forces that must be overcome to change its state. For simple covalent molecules, there are two types of forces to consider:

1. Intramolecular forces (covalent bonds within the molecule): These are strong but are not broken during melting or boiling.
2. Intermolecular forces (forces between molecules): These are the forces that must be overcome during phase changes. In simple covalent molecules, these are typically weak van der Waals forces or dipole-dipole interactions.

Because the intermolecular forces are weak, relatively little energy is needed to separate the molecules from one another. This is why simple covalent substances such as water, methane, and carbon dioxide have low melting and boiling points compared to ionic or metallic substances.

The other options do not explain the low melting and boiling points:

• Having definite shapes describes molecular geometry but does not determine the strength of forces between molecules.
• Being three-dimensional structures is a feature of giant covalent substances (like diamond), which actually have very high melting points.
• Possessing shared electron pairs is what makes them covalent, but the shared pairs (covalent bonds) are not broken during melting or boiling, so they do not account for the low melting/boiling points.

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The rate of reaction measures how quickly a reactant is consumed or a product is formed over a given period. Here, 5 g of iron filings reacted completely with excess dilute \(\text{H}_2\text{SO}_4\) in 10 minutes.

The rate of reaction (in terms of mass of reactant consumed per unit time) is:

Substituting the given values:

The question asks for the rate in grams per hour. Since there are 60 minutes in one hour:

The rate of reaction is 30 g/hr.

A common mistake is to forget the unit conversion from minutes to hours, which would give an incorrect answer of 0.5 g/min. Always check that the units in your final answer match what the question requests.

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Producer gas is a mixture of carbon monoxide (CO) and nitrogen (N₂), while water gas is a mixture of carbon monoxide (CO) and hydrogen (H₂). Both gases contain CO, which is toxic and must be removed for certain industrial applications.

Ammoniacal copper(I) chloride solution (CuCl dissolved in ammonia) is the reagent used to selectively absorb CO from these gas mixtures. The CO molecules form a coordination complex with the copper(I) ions in solution:

\[ \text{CuCl} + \text{CO} + 2\text{NH}_3 \rightarrow [\text{Cu(CO)(NH}_3\text{)}_2]\text{Cl} \]

This reaction is reversible: gentle heating releases the absorbed CO and regenerates the ammoniacal CuCl solution for reuse.

The other gases in these mixtures are not absorbed by this reagent. Hydrogen (H₂) does not form stable complexes with Cu⁺ under these conditions. Nitrogen (N₂) is chemically inert at room temperature. Carbon dioxide (CO₂) would be absorbed by alkaline solutions such as NaOH or KOH, not by ammoniacal CuCl.

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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.

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The electrochemical series (also called the activity series or reactivity series) is a table that ranks metals in order of their tendency to lose their valence electrons and form positive ions. Metals at the top of the series (e.g., potassium, sodium, calcium) lose electrons most readily, while those at the bottom (e.g., gold, platinum) have very little tendency to give up electrons.

The series is determined by measuring the standard electrode potentials of metals. A more negative electrode potential indicates a greater tendency to lose electrons (be oxidised), placing the metal higher in the series.

The other options are not correct:

• The periodic table arranges elements by atomic number and groups them by similar chemical properties, but it does not rank them specifically by their tendency to lose valence electrons in a sequential series.
• "Table of elements" is a vague term that does not refer to a specific scientific arrangement by electron-loss tendency.
• "Periodicals" refers to magazines or journals and has no chemical meaning.

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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.

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The pH of a salt solution depends on the strength of the acid and base from which the salt was formed. A salt formed from a strong acid and a strong base produces a neutral solution with a pH of 7, because neither ion undergoes hydrolysis in water.

Sodium chloride (NaCl) is formed from hydrochloric acid (HCl, a strong acid) and sodium hydroxide (NaOH, a strong base). When dissolved in water, the Na⁺ and Cl^- ions do not react with water, so the solution remains neutral at pH 7.

The other salts behave differently:

• Ammonium chloride (NH₄Cl) is formed from a weak base (NH₃) and a strong acid (HCl). The ammonium ion hydrolyses in water to release H⁺ ions, making the solution acidic (pH below 7).
• Ammonium tetraoxosulphate(VI) ((NH₄)₂SO₄) is also formed from a weak base and a strong acid, producing an acidic solution.
• Sodium trioxocarbonate(IV) (Na₂CO₃) is formed from a strong base (NaOH) and a weak acid (H₂CO₃). The carbonate ion hydrolyses in water to produce OH^- ions, making the solution basic (pH above 7).

Exam tip: To predict the pH of a salt solution, identify the parent acid and base. Strong acid + strong base gives pH 7; strong acid + weak base gives pH below 7; weak acid + strong base gives pH above 7.

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The equation shows ethanol (C₂H₅OH) reacting with ethanoic acid (CH₃COOH) to form ethyl ethanoate (CH₃COOC₂H₅) and water (H₂O).

This is an esterification reaction. Esterification is the reaction between a carboxylic acid and an alcohol to produce an ester and water. It is typically catalysed by a concentrated strong acid such as tetraoxosulphate(VI) acid (H₂SO₄), and the reaction is reversible, indicated by the equilibrium sign (⇌).

The general equation is:

\[\text{Carboxylic acid} + \text{Alcohol} \xrightleftharpoons{\text{H}_2\text{SO}_4} \text{Ester} + \text{Water}\]

The other options do not apply here:

• Condensation is a broader term for reactions where two molecules combine with the loss of a small molecule (often water). While esterification is technically a type of condensation, the specific and more accurate name for this reaction between an acid and an alcohol is esterification.
• Fermentation is the enzymatic conversion of sugars (such as glucose) to ethanol and carbon(IV) oxide.
• Hydrolysis is the reverse of esterification, where an ester is broken down by water (or alkali) into the parent acid and alcohol.

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Fermentation is the biochemical process in which enzymes (particularly zymase, found in yeast) convert glucose into ethanol and carbon dioxide. The overall equation is:

\[\text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{zymase}} 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2\]

This is an anaerobic process, meaning it occurs without oxygen. The key word in the question is enzymatic, which points directly to fermentation, since it is the only process among the given options that is enzyme-catalysed.

Polymerization is the joining of small monomer molecules into a large polymer chain. Hydrogenation is the addition of hydrogen gas across unsaturated bonds, typically using a metal catalyst such as nickel. Saponification is the alkaline hydrolysis of fats or oils to produce soap and glycerol. None of these processes involves the enzymatic breakdown of glucose to ethanol.

Whenever a question mentions the biological or enzymatic conversion of sugars to alcohol, the answer is fermentation.

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A reaction is spontaneous when the Gibbs free energy change is negative, that is, \(\Delta G < 0\). The Gibbs equation relates enthalpy, entropy, and temperature:

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

For the decomposition of phosphorus pentachloride:

\[\text{PCl}_5(g) \rightarrow \text{PCl}_3(s) + \text{Cl}_2(g)\]

Consider the entropy change. On the reactant side there is 1 mole of gas, and on the product side there is 1 mole of solid and 1 mole of gas. Since a solid has much lower entropy than a gas, the total entropy of the products is lower than that of the reactant. Therefore \(\Delta S\) is negative.

With \(\Delta S < 0\), the term \(-T\Delta S\) becomes positive, which adds to \(\Delta G\). For \(\Delta G\) to still be negative (spontaneous), \(\Delta H\) must be sufficiently negative to overcome the positive \(-T\Delta S\) contribution:

\[\Delta G = \Delta H - T\Delta S < 0\]

\[\Delta H < T\Delta S \quad (\text{where } \Delta S < 0, \text{ so } T\Delta S < 0)\]

This means \(\Delta H\) must be negative. An exothermic reaction (\(\Delta H\) is negative) releases enough energy to drive the process forward despite the unfavourable entropy change.

Exam tip: When \(\Delta S\) is negative, only a sufficiently negative \(\Delta H\) can make \(\Delta G\) negative, and such reactions tend to be spontaneous only at low temperatures.

Antwoorddetails

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.

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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.

Antwoorddetails

Iron is extracted from its ore in a blast furnace. The iron that comes directly out of the blast furnace is called pig iron. It contains about 3-4% carbon along with smaller amounts of impurities such as silicon, manganese, phosphorus, and sulphur.

Pig iron is brittle due to its high carbon content and is not suitable for most engineering applications in its raw form. It must be further processed to produce more useful forms of iron and steel:

• Cast iron is produced by remelting pig iron and allowing it to cool in moulds. It still has a relatively high carbon content (2-4%) but has improved properties for casting.
• Wrought iron is nearly pure iron (less than 0.1% carbon) produced by removing most of the carbon and impurities from pig iron. It is soft, malleable, and resistant to corrosion.
• Carbon steel is produced by carefully controlling the carbon content of iron (0.1-1.5%) to achieve specific mechanical properties.

The iron that comes directly from the blast furnace, before any further refining, is pig iron.

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The structure shown is R-C(=O)-NH-H, which contains a carbonyl group (C=O) directly bonded to a nitrogen atom bearing hydrogen atoms. This is the defining arrangement of the amide functional group (-CONH₂).

An alkanamide (also called an amide) has the general formula R-CONH₂, where R is an alkyl group. The key feature distinguishing it from the other options is the simultaneous presence of both the C=O and the N-H bonds on the same carbon.

An alkylamine (R-NH₂) has nitrogen bonded to an alkyl group but no carbonyl. An alkanone (R-CO-R') has a carbonyl flanked by two carbon groups with no nitrogen. An amino acid would require both an amine group (-NH₂) and a carboxyl group (-COOH) on the same molecule, which is not the case here.

Antwoorddetails

A reaction is feasible (spontaneous) when the Gibbs free energy change is negative: \(\Delta G < 0\). The relationship between Gibbs free energy, enthalpy, and entropy is:

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

The question states that \(\Delta G^\circ\) is negative. To determine which combination of \(\Delta H\) and \(\Delta S\) guarantees this, consider each option:

• If \(\Delta H\) is positive and \(\Delta S\) is positive: \(\Delta G = (+) - T(+)\). This is negative only at sufficiently high temperatures, so feasibility is not guaranteed at all temperatures.
• If \(\Delta H = 0\) and \(\Delta S\) is positive: \(\Delta G = 0 - T(+) = -T\Delta S\), which is always negative at any temperature above 0 K. This guarantees a negative \(\Delta G\).
• If \(\Delta H\) is positive and \(\Delta S\) is negative: \(\Delta G = (+) - T(-) = (+) + T|\Delta S|\), which is always positive. The reaction would never be feasible.
• If \(\Delta S = 0\): \(\Delta G = \Delta H\), and feasibility depends entirely on the sign of \(\Delta H\), which is not specified.

The only option that ensures \(\Delta G\) is negative under all conditions is \(\Delta H = 0\) and \(\Delta S\) is positive, because the \(-T\Delta S\) term is always negative when \(\Delta S > 0\).

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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.