1. Combustion Test:

- C₂H₂ burns with a sooty/luminous flame due to higher carbon content.

- C₂H₄ burns with a non-sooty flame.

2. Ammoniacal Silver Nitrate Test (Tollen's reagent):

- C₂H₂ reacts to form a white precipitate of silver acetylide.

- C₂H₄ shows no reaction.

1. Position of ions in the electrochemical series:

- Ions lower in the series are discharged more readily than those higher up.

2. Concentration of ions:

- Higher concentration of a particular ion can favor its discharge over another.

3. Nature of the electrodes:

- Some electrodes (e.g., platinum or copper) can participate in the reaction, influencing which ion is discharged.

Complete balanced ionic equation (in acidic medium):

MnO₄⁻(aq) + 8H⁺(aq) + 5e⁻ → Mn²⁺(aq) + 4H₂O(l)

Explanation: This is a reduction half-equation for permanganate ion (MnO₄⁻) in acidic solution.

1. Non-toxicity and corrosion resistance:

- Aluminium does not react with food or alter its taste; it resists corrosion, especially due to its oxide layer.

2. Lightweight and malleable:

- It is easy to shape into foils, cans, and other packaging forms without adding much weight.

3. Acts as a barrier:

- Aluminium provides an excellent barrier to light, air, moisture, and bacteria, preserving food quality.

Solubility of a salt is defined as the maximum amount of the salt (solute) that can dissolve in a specific amount of solvent (usually water) at a given temperature to form a saturated solution.

It is usually expressed in grams of salt per 100 grams of water (g/100g) or in moles per liter (mol/L).

At this point, the rate at which the salt dissolves equals the rate at which it precipitates out of solution, meaning the solution is in dynamic equilibrium.

According to the Kinetic Theory of Matter, all matter is made up of tiny particles (atoms or molecules) that are in constant motion.

When a solid is heated, the heat energy is absorbed by the particles, increasing their kinetic energy.

This causes the particles to vibrate more vigorously about their fixed positions. As heating continues, the vibrations become strong enough to overcome the intermolecular forces holding the particles in the solid structure.

Eventually, the solid melts into a liquid as the particles gain enough energy to move more freely past one another while still being in close contact.

A substitution reaction is a type of chemical reaction in which one atom or group of atoms in a compound is replaced or exchanged by another atom or group.

It commonly occurs in organic chemistry, especially with alkanes and halogens, where a hydrogen atom is replaced by a halogen atom (e.g., chlorine or bromine).

Example: CH₄ + Cl₂ → CH₃Cl + HCl
(Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.)

Substitution reactions are usually classified into nucleophilic, electrophilic, or radical substitution depending on the nature of the reacting species.

Step 1: Determine the molar mass of Mg(NO₃)₂

Mg = 24.0
N = 14.0 × 2 = 28.0
O = 16.0 × 6 = 96.0

Total molar mass = 24.0 + 28.0 + 96.0 = 148.0 g/mol

Step 2: Calculate the percentage by mass of oxygen

%O = (Mass of O / Molar Mass of Compound) × 100

%O = (96.0 / 148.0) × 100 ≈ 64.86%

Answer: The percentage by mass of oxygen in magnesium trioxonitrate (V) is approximately 64.86%.

In quantitative analysis, especially in titrations, indicators are used to show the end point of the reaction. Common indicators include:

• Methyl orange – used in strong acid vs weak base titrations.


• Phenolphthalein – used in strong base vs weak acid titrations.


• Starch solution – used as an indicator in iodometric titrations (e.g., titration involving iodine).

The choice of indicator depends on the type of acid-base reaction involved.

(i) Differences between Ionization Energy and Electron Affinity:

• Ionization energy is the energy required to remove an electron from a neutral gaseous atom, forming a cation.
• Electron affinity is the energy released when a neutral gaseous atom gains an electron to form an anion.
• Ionization energy is generally endothermic (absorbs energy), while electron affinity is generally exothermic (releases energy).

(ii) Type of Reaction:

The reaction: 2SO₂(g) + O₂(g) → 2SO₃(g)

is a combination (or synthesis) reaction, because two or more reactants combine to form a single product.

(i) Calculation using dilution formula:

Use the formula: C₁V₁ = C₂V₂
Where:

C₁ = 12.6 mol/dm³ (initial concentration)

V₁ = ? (volume to find)

C₂ = 3.0 mol/dm³ (final concentration)

V₂ = 5.0 dm³ (final volume)

V₁ = (C₂ × V₂) / C₁

V₁ = (3.0 × 5.0) / 12.6 ≈ 1.19 dm³

Answer: Approximately 1.19 dm³ of HCl must be added.

(ii) Why sodium oxide forms an alkaline solution:

Sodium oxide (Na₂O) reacts with water to form sodium hydroxide (NaOH), a strong base:

Na₂O + H₂O → 2NaOH

Sodium hydroxide dissociates completely in water to release hydroxide ions (OH⁻), which makes the solution alkaline.

(i) Why MgO has a higher melting point than NaCl:

MgO consists of magnesium ions (Mg²⁺) and oxide ions (O²⁻), while NaCl consists of sodium ions (Na⁺) and chloride ions (Cl⁻).

The electrostatic attraction in MgO is stronger due to the higher charges (+2 and −2), compared to the +1 and −1 charges in NaCl.

Stronger ionic bonds in MgO require more energy to break, resulting in a much higher melting point than NaCl.

(ii) Why CO₂ is a non-polar molecule:

Although the C=O bonds in carbon dioxide are polar due to a difference in electronegativity between carbon and oxygen, the molecule is linear and symmetrical.

This symmetry causes the bond dipoles to cancel out, making the overall molecule non-polar.

(i) Two periodic properties that increase across a period:

• Electronegativity: The ability of an atom to attract electrons increases across a period due to increasing nuclear charge.


• Ionization energy: More energy is required to remove an electron as you move from left to right across a period.

(ii) Acids in increasing order of acidity:

HF < HCl < HBr < HI

(iii) Reason:

Acid strength increases down the group because the H−X bond becomes weaker and easier to break. HI has the weakest bond and therefore releases H⁺ ions more easily, making it the strongest acid among them.

(i) Reasons why they form a homologous series:

• Each successive member differs by a −CH₂− group.


• They all have the same general formula and similar chemical properties.

(ii) General name given to the compounds:

Carboxylic acids

(iii) Functional group present:

Carboxyl group (−COOH)

(iv) Why CH₃COOH has a higher boiling point than CH₃CH₂OH:

CH₃COOH (acetic acid) forms stronger hydrogen bonds and also forms dimers in the liquid phase, effectively increasing the molecular mass and intermolecular forces.

These stronger interactions require more energy to break, resulting in a higher boiling point compared to CH₃CH₂OH (ethanol).

(i) Formula of Y:

Balance the hydrogen and carbon atoms:

Left: C₁₇H₃₆

Right (so far):

2C₂H₄ = C₄H₈, C₈H₁₈

Total so far: C₁₂H₂₆

Difference:

C₅H₁₀

→ Y = C₅H₁₀

(ii) Homologous series of Y:

Alkenes (Y is an unsaturated hydrocarbon)

(iii) Type of reaction:

Cracking (thermal decomposition of large hydrocarbons into smaller ones)

(iv) Volume of ethene at s.t.p from 0.2 mol of C₁₇H₃₆:

From equation: 1 mol of C₁₇H₃₆ → 2 mol of C₂H₄

Therefore, 0.2 mol → 0.2 × 2 = 0.4 mol of C₂H₄

Volume = 0.4 mol × 22.4 dm³/mol

= 8.96 dm³

(i) What is an ideal gas?

An ideal gas is a hypothetical gas that perfectly follows all the assumptions of the kinetic molecular theory under all conditions of temperature and pressure.

It has no intermolecular forces, and the gas particles occupy no volume.

(ii) Assumptions made in explaining the behavior of gases:

• Gas particles are in constant random motion.


• There are no attractive or repulsive forces between particles.


• The volume of individual gas particles is negligible compared to the volume of the container.


• Collisions between gas particles and the container walls are perfectly elastic (no energy is lost).


• The average kinetic energy of gas particles is directly proportional to the temperature in Kelvin.

(iii) Explanation: Basic Nature of Oxides of Strongly Electropositive Metals

Oxides of strongly electropositive metals (like Na, Ca, and K) are basic because the metal atoms donate electrons readily, forming metal oxides that react with water to produce alkaline solutions (metal hydroxides).

For example, Na₂O + H₂O → 2NaOH.

These metal oxides contain O²⁻ ions that react with water to form OH⁻ ions, giving rise to basic properties.

(i) Why NaH is basic:

Sodium hydride (NaH) contains the hydride ion (H⁻), which is a strong base.

When NaH reacts with water, it donates H⁻ to form hydroxide ions (OH⁻):

NaH + H₂O → NaOH + H₂↑

This shows NaH acts as a base by producing hydroxide ions in solution.

(ii) Why NaH is a reducing agent:

The hydride ion (H⁻) in NaH can donate electrons to other species, reducing them. In the reaction with water, H⁻ reduces H₂O to hydrogen gas:

H⁻ + H₂O → H₂ + OH⁻

Therefore, NaH acts as a reducing agent because it supplies electrons and causes the reduction of other substances, especially in organic reactions and metal halide reductions.

(i) Charles' Law:

Charles' Law states that the volume of a fixed mass of gas is directly proportional to its absolute temperature (in Kelvin), provided pressure remains constant.

Mathematically:

V ∝ T or V/T = constant

This means that as the temperature of a gas increases, its volume also increases if the pressure is unchanged.

(ii) Periodic Law:

The Periodic Law states that the physical and chemical properties of elements are periodic functions of their atomic numbers.

This means that when elements are arranged in order of increasing atomic number, elements with similar properties recur at regular intervals (i.e., periodically). This is the basis for the structure of the modern periodic table.

(i) Balanced Chemical Equation:

NaCl(s) + H₂SO₄(conc) → NaHSO₄(s) + HCl(g)

This reaction involves heating sodium chloride (table salt) with concentrated sulfuric acid to release hydrogen chloride gas.

(ii) Advantages of Hard Water:

• Hard water contains calcium and magnesium ions which are essential for human health, particularly in bone and teeth development.


• It helps to reduce the risk of lead poisoning by forming insoluble lead salts that are not easily absorbed in the body.


• Hard water is preferred in brewing and tanning industries due to its mineral content.


• It may also reduce the solubility of toxic metal salts in water.

(i) Conversion of Bauxite to Pure Alumina:

Bauxite, which mainly contains aluminium oxide (Al₂O₃) along with impurities like silica, iron oxides, and titanium oxide, is first purified using the Bayer process:

• The bauxite is crushed and treated with hot concentrated sodium hydroxide (NaOH) solution.


• Aluminium oxide dissolves in the NaOH forming soluble sodium aluminate (NaAlO₂), while impurities like Fe₂O₃ and TiO₂ remain undissolved and are filtered off.


• The solution is cooled and seeded with pure alumina crystals, causing aluminium hydroxide (Al(OH)₃) to precipitate.


• The Al(OH)₃ is then filtered, dried, and heated (calcined) to form pure alumina (Al₂O₃).

(ii) Properties of Metals Accounted for by Their Structure:

• Malleability: Metals can be hammered or rolled into sheets without breaking due to the ability of atoms to slide over each other in layers.


• Ductility: Metals can be drawn into wires because of the presence of mobile electrons that maintain bonding as atoms move.


• Electrical conductivity: Free-moving electrons in the metallic lattice allow electric current to pass easily through metals.


• Thermal conductivity: Delocalized electrons also transfer heat efficiently through the metallic structure.


• Lustre: Metals reflect light due to the presence of free electrons on the surface.

(i)(I) Effect of Adding a Catalyst:

The addition of a catalyst increases the rate of the reaction by lowering the activation energy, but it does not affect the position of equilibrium or the overall yield of ammonia.

(i)(II) Effect of Increasing Temperature:

Since the formation of ammonia is an exothermic reaction (ΔH is negative), increasing the temperature shifts the equilibrium to the left, favoring the decomposition of ammonia and reducing the yield.

(ii) Methods of Collecting Dry Gases:

• By upward delivery (for gases denser than air)


• By downward delivery (for gases less dense than air)


• By collection over water (if the gas is insoluble in water)

(iii) Reason for Different Collection Methods:

The method of collection depends on the gas's physical properties, such as its density relative to air and its solubility in water.

(i) Process When Coke Reacts with Air:

When coke (carbon) reacts with limited supply of air at high temperatures, it undergoes partial combustion to produce carbon monoxide (CO), a process known as gasification.

(ii) Name of the Product:

Carbon monoxide (CO)

(iii) Chemical Equation for Reaction with Steam:

C(s) + H₂O(g) → CO(g) + H₂(g)

(iv) Use of the Product:

Used as a fuel and in the production of synthetic gas (syngas) for chemical manufacturing.

(v) Advantage of the Product:

It is a clean-burning fuel that produces fewer pollutants compared to traditional fossil fuels.

(i) Industrial Preparation of Oxygen:

Oxygen is prepared industrially through the fractional distillation of liquid air:

• Air is first filtered to remove dust and cooled to about -200°C to liquefy it.


• Carbon dioxide and water vapor are removed before liquefaction to avoid solidification.


• Liquid air is then subjected to fractional distillation:
• Nitrogen (boiling point −196°C) distills off first.


• Oxygen (boiling point −183°C) is collected after nitrogen has been separated.


• The oxygen is then stored in high-pressure cylinders for commercial use.

(ii) Uses of Oxygen:

• Used in hospitals for respiration support and life support systems.


• Used in oxy-acetylene torches for cutting and welding metals.


• Essential in steel manufacturing for oxidizing impurities.


• Used in rocket propulsion as an oxidizer.


• Supports combustion in various industrial processes.


• Used in water treatment and sewage processing.


• Involved in the synthesis of important chemicals like sulfuric acid and nitric acid.

(i) Balanced Equations:

1. Formation of sulphur (IV) oxide (SO₂):
   
   S(s) + O₂(g) → SO₂(g)
   
   
2. Conversion of sulphur (IV) oxide to sulphur (VI) oxide (SO₃):
   
   2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
   
   ΔH = −197 kJ/mol
   
   
3. Formation of tetraoxosulphate (VI) acid:
   
   SO₃(g) + H₂O(l) → H₂SO₄(aq)
   

(ii) Conditions that Favor the Conversion of SO₂ to SO₃:

• Moderate temperature of about 450°C (to favor yield and maintain a reasonable rate).


• Pressure of about 1−2 atm (though pressure has a limited effect on yield).


• Use of vanadium(V) oxide (V₂O₅) as catalyst to speed up the reaction.


• Excess oxygen to shift equilibrium to the right.

(i) Important Properties of Calcium:

• It is a soft, silvery-white alkaline earth metal.


• It has a relatively low density (1.55 g/cm³) and low melting point (842°C).


• Calcium reacts with water to produce calcium hydroxide and hydrogen gas.


• It is a good conductor of electricity and heat.


• It readily forms calcium ions (Ca²⁺) by losing two electrons.

(ii) Uses of Calcium:

• Used in the manufacture of cement and lime (CaO).


• Important in metallurgy for removing impurities from other metals.


• Essential nutrient for bone and teeth formation in humans and animals.


• Used as a reducing agent in the extraction of some metals.