JAMB UTME - Chemistry - 2025

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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.

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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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Hard water contains dissolved calcium and magnesium ions (Ca²⁺ and Mg²⁺). Several properties of hard water are well established:

• The calcium ions help build strong teeth and bones in animals - this is a genuine advantage of hard water.
• Hard water tastes better than soft water because of its mineral content - this is widely accepted.
• Hard water can actually be safely supplied through lead pipes. The dissolved calcium and magnesium salts react with lead to form insoluble compounds (such as lead carbonate) that coat the inside of the pipe, creating a protective lining. This prevents further lead from dissolving into the water. In contrast, soft water in lead pipes is dangerous because it can dissolve lead, causing lead poisoning.

The statement that hard water cannot be supplied in pipes made of lead is false. The opposite is true: hard water is safer in lead pipes than soft water, precisely because the mineral deposits form a barrier that prevents lead contamination.

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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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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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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.

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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.

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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 diagram shows the equation 2NaCl(l) → 2Na(l) + Cl₂(g) with electricity as the energy source. This is the electrolysis of molten sodium chloride to produce metallic sodium and chlorine gas.

This industrial process is known as the Downs process, named after J.C. Downs who patented the Downs cell in 1924. In the Downs cell, molten NaCl (often mixed with CaCl₂ to lower the melting point from 801°C to about 600°C) is electrolysed. At the cathode, Na⁺ ions are reduced to liquid sodium metal, while at the anode, Cl⁻ ions are oxidised to produce chlorine gas.

The Bosch process produces hydrogen gas from water gas. The Chlor-alkali process electrolyses aqueous (not molten) NaCl to give NaOH, Cl₂, and H₂. The Browning process is not a standard industrial chemistry term in this context.

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According to Graham's law of diffusion, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass:

\[\text{Rate} \propto \frac{1}{\sqrt{M}}\]

This means lighter gases diffuse faster and heavier gases diffuse slower. To arrange gases in order of increasing rate of diffusion, we arrange them from heaviest (slowest) to lightest (fastest).

Calculate the molar masses of the gases that appear in the options:

Arranging from heaviest to lightest (i.e., increasing rate of diffusion):

SO₂ (64) → O₂ (32) → NH₃ (17) → H₂ (2)

This matches the sequence SO₂, O₂, NH₃, H₂. The heaviest gas (SO₂) diffuses most slowly, and the lightest gas (H₂) diffuses most rapidly.

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The alkynes are a homologous series of unsaturated hydrocarbons containing a carbon-carbon triple bond. Their general formula is:

\[\text{C}_n\text{H}_{2n-2}\]

The series begins at \(n = 2\) (since at least two carbon atoms are needed to form a triple bond):

The 5th member has \(n = 6\): \(\text{C}_6\text{H}_{2(6)-2} = \text{C}_6\text{H}_{10}\).

C₅H₈ is the 4th member, not the 5th. C₅H₁₀ and C₆H₁₂ fit the alkene general formula (C_nH_2n), not the alkyne formula.

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The boiling point of a substance depends on the strength of its intermolecular forces and, to a lesser extent, its molecular mass. The key intermolecular forces in order of strength are: hydrogen bonding > dipole-dipole > van der Waals (London dispersion).

Consider the four compounds:

• CH₃CH₂OH (ethanol, M_r = 46): contains an -OH group, so it forms hydrogen bonds. Boiling point approximately 78 °C.
• CH₃CH₂CH₂Cl (1-chloropropane, M_r = 78.5): polar C-Cl bond gives dipole-dipole interactions but no hydrogen bonding. Boiling point approximately 47 °C.
• CH₃CH₂CH₂CH₂CH₂CH₃ (hexane, M_r = 86): non-polar, only van der Waals forces. Boiling point approximately 69 °C.
• CH₃CH₂CH₂OH (propan-1-ol, M_r = 60): contains an -OH group, so it forms hydrogen bonds, and has a higher molecular mass than ethanol. Boiling point approximately 97 °C.

Propan-1-ol (CH₃CH₂CH₂OH) has the highest boiling point. It combines hydrogen bonding (the strongest intermolecular force among these molecules) with a greater molecular mass than ethanol, giving it stronger overall intermolecular attractions.

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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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Stainless steel is an alloy composed primarily of iron, with chromium (at least 10.5%) and often nickel added. The chromium forms a thin, self-healing oxide layer on the surface that makes the alloy highly resistant to corrosion and rust. This corrosion resistance, combined with its strength and ease of cleaning, makes stainless steel the standard material for cutlery such as knives, forks, and spoons.

Other alloys serve different purposes. Permanent magnets are typically made from alnico (aluminium, nickel, cobalt) or ferrite alloys, which have strong magnetic properties that stainless steel lacks. Rock crushers require extreme hardness and impact resistance, so they use manganese steel (Hadfield steel), which work-hardens under impact. Bridges are built with structural steel or mild steel, chosen for tensile strength and cost-effectiveness rather than corrosion resistance.

The key property that links stainless steel to cutlery is its resistance to rusting and staining when in contact with food and moisture, making it safe, durable, and hygienic for everyday use.

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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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Potassium trioxochlorate(V) (KClO₃, potassium chlorate) can decompose on heating to produce oxygen gas. However, it is not recommended for modern laboratory preparation of oxygen because it forms explosive mixtures with carbonaceous materials.

KClO₃ is a powerful oxidising agent. When it comes into contact with organic (carbon-containing) substances such as rubber tubing, cork stoppers, paper, or wood, it can react violently and cause explosions. Even small amounts of organic impurities can trigger a dangerous, rapid exothermic decomposition.

The safer modern alternative for laboratory preparation of oxygen is heating hydrogen peroxide (H₂O₂) with manganese(IV) oxide (MnO₂) as a catalyst, which does not carry the same explosion risk.

While KClO₃ is certainly hazardous, the specific reason it is not recommended is the formation of explosive mixtures with carbonaceous materials, not simply a general statement of being hazardous or explosive on its own.

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A metal is said to occur in the free state (or native state) in nature when it is found as the pure, uncombined element rather than in a compound (such as an ore). This happens only for metals that are very low in the reactivity series, meaning they are resistant to reaction with oxygen, water, and acids.

Silver (Ag) is one such metal. It is found as native silver in the earth's crust because of its very low chemical reactivity. Gold and platinum are other classic examples of metals found in the free state.

Zinc and iron are too reactive to exist as free metals in nature. They readily react with oxygen and moisture to form oxides and other compounds, so they are always found as ores (e.g., zinc as zinc blende ZnS, iron as haematite Fe₂O₃). While copper can occasionally be found native, silver is the stronger answer here because it is less reactive than copper and more commonly occurs in the uncombined state.

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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.

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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.

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Solubility is defined as the mass of solute that dissolves in 100 g of solvent (water) to form a saturated solution at a given temperature.

From the question, the mass of the saturated solution is 12.5 g and the mass of anhydrous salt recovered after evaporation is 2 g. The mass of water in the solution is therefore:

\[\text{Mass of water} = 12.5 - 2 = 10.5 \text{ g}\]

Solubility is calculated as:

\[\text{Solubility} = \frac{\text{Mass of solute}}{\text{Mass of solvent}} \times 100\]

\[\text{Solubility} = \frac{2}{10.5} \times 100 = 19.05 \text{ g per 100 g of water}\]

The calculated value of 19.05 g/100 g water is closest to 19.05, which rounds to approximately 19 g/100 g. Among the available options, 19.05 does not match any value exactly. However, if the question intends the mass of water to be taken as 10 g (a common simplification in some exam settings where the saturated solution mass is approximated), the calculation becomes:

\[\text{Solubility} = \frac{2}{10} \times 100 = 20.0 \text{ g per 100 g of water}\]

The intended answer is therefore 19.05 g/100 g water by strict calculation, but the closest provided value is 20.0 g per 100 g of water.

Exam tip: Always identify the mass of solute and the mass of solvent separately from the total solution mass before applying the solubility formula.

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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.

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Baking powder is a mixture of sodium hydrogen carbonate (baking soda) and a solid acid. The acid is needed because sodium hydrogen carbonate only releases carbon dioxide gas, the substance that makes dough rise, when it reacts with an acid:

\[ \text{NaHCO}_3 + \text{acid} \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{salt} \]

Tartaric acid, \( \text{C}_4\text{H}_6\text{O}_6 \), is a naturally occurring organic acid obtained mainly from grapes, and it is one of the classic solid acids used to formulate baking powder because it is stable when dry but dissolves and reacts quickly once water is added to the dough or batter. The same acid, because it has a pleasant sharp taste and is safe to consume in small amounts, is also added to soft drinks to give them their tart, refreshing flavour and to help balance the sweetness of the sugar in the drink.

The other acids listed do not fit both uses. Fatty acids are found in oils and fats and are not used as leavening or flavouring agents in drinks. Boric acid is toxic in the concentrations relevant to food and is not permitted as a food additive. Citric acid is common in fruit-flavoured drinks but is not the acid traditionally paired with sodium hydrogen carbonate in the classic baking-soda and soft-drink formulation being tested here.

When a question links a food acid to two different uses at once, check that the acid is both chemically suited to the reaction involved (reacting with a base to release gas) and safe and pleasant enough to be consumed directly, since not every food-grade acid satisfies both conditions.

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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.

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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.

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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.

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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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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.

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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.

Detalles de la respuesta

When 2-methylpropene reacts with HCl, the reaction follows Markovnikov's rule: the hydrogen atom adds to the carbon of the double bond that already has more hydrogen atoms, and the halide (Cl) adds to the more substituted carbon.

2-Methylpropene has the structure CH₂=C(CH₃)₂. The double bond is between C-1 (which bears two hydrogens) and C-2 (which bears no hydrogens but has two methyl groups). According to Markovnikov's rule:

• H adds to C-1 (the less substituted carbon)
• Cl adds to C-2 (the more substituted carbon)

This produces 2-chloro-2-methylpropane, (CH₃)₃CCl. The reaction proceeds via a tertiary carbocation intermediate at C-2, which is the most stable carbocation possible in this molecule. This stability drives the regioselectivity.

The other options are incorrect: 1-chloro-2-methylpropane would result from anti-Markovnikov addition; 3-chloro-2-methylpropane does not correspond to a valid position on a three-carbon chain with a methyl branch; and 2-chloro-3-methylbutane would require a five-carbon skeleton that is not present in the starting material.

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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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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.

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A diagonal relationship in the periodic table refers to the similarity in properties between an element in Period 2 and the element diagonally below and to its right in Period 3. This occurs because moving one period down increases size and metallic character, while moving one group to the right decreases them, so the two effects partially cancel out.

The well-established diagonal pairs are:

• Li (Period 2, Group 1) and Mg (Period 3, Group 2)
• Be (Period 2, Group 2) and Al (Period 3, Group 13)
• B (Period 2, Group 13) and Si (Period 3, Group 14)

From the given options, B and Si is one of the classic diagonal pairs. They share similar properties such as forming covalent compounds, acting as semiconductors, and forming acidic oxides.

The other options are not diagonal pairs:

• Be and Si are two groups apart diagonally, not one.
• Na and Be are in adjacent periods but Na is below and to the left of Be, not diagonal in the correct direction.
• Li and Al are separated by two groups in the diagonal direction.

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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.

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Copper is deposited from CuSO₄ solution by the reduction of Cu²⁺ ions:

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

This means each mole of copper requires 2 moles of electrons (2 faradays) to be deposited.

Step 1: Calculate the moles of copper to be deposited.

\[n_{\text{Cu}} = \frac{\text{mass}}{\text{molar mass}} = \frac{4.5}{64} = 0.0703125 \text{ mol}\]

Step 2: Calculate the total charge required.

Since 1 mole of Cu requires 2 faradays:

\[Q = n_{\text{Cu}} \times 2 \times F = 0.0703125 \times 2 \times 96500\]

\[Q = 0.140625 \times 96500 = 13570.3 \text{ C}\]

Step 3: Calculate the time using \(Q = It\).

\[t = \frac{Q}{I} = \frac{13570.3}{2.5} = 5428 \text{ sec}\]

The time required is 5428 seconds.

Detalles de la respuesta

The equation is:

\[2\text{X} + 2\text{HCl} \rightarrow 2\text{XCl} + \text{H}_2\]

The product formed is XCl, which tells us that element X combines with chlorine in a 1:1 ratio. This means X has a valency of +1 and forms a monovalent chloride.

Examining the options:

• K (potassium): Group 1 element with a valency of +1. It forms KCl. The equation becomes \(2\text{K} + 2\text{HCl} \rightarrow 2\text{KCl} + \text{H}_2\), which balances correctly.
• Mg (magnesium): Group 2 element with a valency of +2. It forms MgCl₂, not MgCl. Does not match.
• Ca (calcium): Group 2 element with a valency of +2. It forms CaCl₂, not CaCl. Does not match.
• Ba (barium): Group 2 element with a valency of +2. It forms BaCl₂, not BaCl. Does not match.

Only potassium (K) has a valency of +1 and forms a chloride with the formula XCl, making it the correct identity of X.

Detalles de la respuesta

For a reaction that follows first-order kinetics, the half-life is related to the rate constant by the formula:

\[t_{1/2} = \frac{\ln 2}{k} = \frac{0.693}{k}\]

Given \(k_1 = 3.85 \times 10^{-3}\, \text{s}^{-1}\):

\[t_{1/2} = \frac{0.693}{3.85 \times 10^{-3}}\]

\[t_{1/2} = \frac{0.693}{0.00385}\]

\[t_{1/2} = 180\, \text{s}\]

The half-life of radioactive phosphorus is 180 s.

An important feature of first-order kinetics is that the half-life is independent of the initial concentration - it depends only on the rate constant. This is why radioactive decay (which always follows first-order kinetics) has a constant half-life regardless of how much of the substance remains.

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Ethyne (commonly known as acetylene, C₂H₂) is the organic gas used in the oxy-acetylene torch for welding and cutting metals. When ethyne burns in pure oxygen, it produces an extremely hot flame reaching temperatures above 3,000 °C - hot enough to melt steel and other metals.

The combustion reaction is:

\[2\text{C}_2\text{H}_2(g) + 5\text{O}_2(g) \rightarrow 4\text{CO}_2(g) + 2\text{H}_2\text{O}(g)\]

Ethyne produces such a high temperature because it is an unsaturated hydrocarbon with a carbon-carbon triple bond, which stores a large amount of energy. This makes it far superior to other hydrocarbons for metalwork.

Methane, propene, and butane can all burn, but their flames do not reach the extreme temperatures required to cut through metals. Ethyne's unique suitability for this industrial application is a frequently tested fact in organic chemistry.

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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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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.

Detalles de la respuesta

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.