The quantum numbers for the last electron in the ground state of sodium (Na, atomic number 11) are
Na: 1s²2s²2p⁶3s¹; last electron in 3s orbital: n=3, l=0 (s), m=0, s=+1/2.
The volume of 0.5 mol/dm³ H₂SO₄ required to neutralize 25 cm³ of 0.2 mol/dm³ KOH is [1 cm³ = 0.001 dm³]
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O; moles KOH = 0.2 × 0.025 = 0.005 mol; moles H₂SO₄ = 0.005/2 = 0.0025 mol; volume H₂SO₄ = 0.0025/0.5 = 0.005 dm³ = 10 cm³.
The type of hybridization in the carbon atom of ethanoic acid (CH₃COOH) in the carboxyl group is
The carboxyl carbon forms one double bond (C=O) and two single bonds (C-O, C-C), requiring sp² hybridization.
The rate of decomposition of hydrogen peroxide is increased by adding
MnO₂ acts as a catalyst, lowering the activation energy for H₂O₂ decomposition into water and oxygen.
The enthalpy change for the reaction C(s) + O₂(g) → CO₂(g) is -393.5 kJ/mol. The formation of 4.4 g of CO₂ releases [C = 12, O = 16]
Molar mass CO₂ = 44 g/mol; moles CO₂ = 4.4/44 = 0.1 mol; energy released = 0.1 × 393.5 = 39.35 kJ.
In the electrolysis of dilute CuSO₄ solution using copper electrodes, the mass of the cathode increases because
At the cathode, Cu²⁺ + 2e⁻ → Cu; copper is deposited, increasing cathode mass.
The pH of a solution formed by mixing 50 cm³ of 0.1 M HCl with 50 cm³ of 0.1 M NaOH is
HCl + NaOH → NaCl + H₂O; moles HCl = moles NaOH = 0.1 × 0.05 = 0.005 mol; complete neutralization forms a neutral solution, pH = 7.
The element with the electron configuration 1s²2s²2p⁶3s²3p³ belongs to
Valence electrons: 3s²3p³ = 5 electrons; belongs to Group 5 (e.g., phosphorus).
The compound formed when aluminium reacts with oxygen is
4Al + 3O₂ → 2Al₂O₃; aluminium oxide has the formula Al₂O₃.
The IUPAC name of the compound CH₃CH(OH)CH₂CH₃ is
Four-carbon chain with -OH on carbon 2: butan-2-ol.
The process used to separate a mixture of liquids with close boiling points is
Fractional distillation separates liquids based on slight differences in boiling points.
The standard electrode potential of Zn²⁺/Zn is -0.76 V and Cu²⁺/Cu is +0.34 V. The EMF of the cell Zn|Zn²⁺||Cu²⁺|Cu is
EMF = E_cathode - E_anode = 0.34 - (-0.76) = 0.34 + 0.76 = 1.10 V.
The gas that forms a red-brown vapour when heated is
NO₂ forms a red-brown vapour, especially when heated.
The functional group in CH₃COCH₃ is
CH₃COCH₃ (propanone) contains a C=O group, characteristic of ketones.
The effect of adding a catalyst to a reversible reaction at equilibrium is
A catalyst speeds up both forward and reverse reactions, reducing the time to reach equilibrium without shifting it.
The monomer used to produce polyethene is
Polyethene is formed by polymerizing ethene (C₂H₄).
The compound responsible for the smell of rotten eggs is
H₂S has a characteristic rotten egg smell.
The mass of silver deposited when a current of 2 A is passed through a silver nitrate solution for 965 seconds is [Ag = 108, 1 F = 96500 C]
Q = I × t = 2 × 965 = 1930 C; moles Ag = 1930/96500 = 0.02 mol; mass Ag = 0.02 × 108 = 2.16 g.
The property of elements that increases across a period from left to right is
Electronegativity increases across a period due to increasing nuclear charge, attracting electrons more strongly.
The industrial process used to extract iron from its ore is
Iron is extracted from hematite in a blast furnace using carbon monoxide as a reducing agent.
The molecular formula of a compound with empirical formula CH₂ and vapour density of 42 is [C = 12, H = 1]
Molar mass = 2 × 42 = 84; empirical mass CH₂ = 14; n = 84/14 = 6; molecular formula = (CH₂)₆ = C₆H₁₂.
The reaction CH₃CH=CH₂ + HBr → CH₃CHBrCH₃ is an example of
Propene undergoes electrophilic addition with HBr across the double bond.
The compound used to soften hard water is
Sodium carbonate precipitates Ca²⁺ as CaCO₃, softening hard water.
The coordination number of the central ion in [Co(NH₃)₆]³⁺ is
Six NH₃ ligands are bonded to Co³⁺, giving a coordination number of 6.
The volume of a gas at 27°C and 760 mmHg is 250 cm³. Its volume at 127°C and 800 mmHg is
P₁V₁/T₁ = P₂V₂/T₂; V₂ = (760 × 250 × 400)/(800 × 300) ≈ 280 cm³ (T in Kelvin: 27°C = 300 K, 127°C = 400 K).
The substance used to vulcanize rubber is
Sulphur forms cross-links in rubber, increasing its strength and elasticity.
The equilibrium constant Kc for the reaction 2HI(g) ⇌ H₂(g) + I₂(g) will increase if
The reaction is endothermic; increasing temperature shifts equilibrium to the right, increasing Kc.
The major pollutant from automobile exhausts is
Carbon monoxide is a toxic gas produced by incomplete combustion in engines.
The oxidation number of nitrogen in NH₄NO₃ is
NH₄⁺: N = -3 (4H = +4, total = +1); NO₃⁻: N = +5 (3O = -6, total = -1).
The process of converting linear alkanes to branched alkanes is called
Reforming restructures alkanes to improve fuel quality, often producing branched isomers.
The half-life of a radioactive isotope is 12 hours. The fraction of the original sample remaining after 36 hours is
36/12 = 3 half-lives; fraction remaining = (1/2)³ = 1/8.
The compound formed when ethanol is heated with concentrated H₂SO₄ at 180°C is
Concentrated H₂SO₄ dehydrates ethanol to ethene (C₂H₄) at 180°C via elimination.
The raw material used in the production of cement is
Limestone (CaCO₃) is heated with clay to produce cement clinker.
The type of isomerism exhibited by CH₃CH₂CH=CHCH₃ is
Pent-2-ene has a double bond, allowing cis-trans (geometric) isomerism.
The gas used in the Haber process for ammonia production is
N₂ reacts with H₂ to form NH₃ in the Haber process under high pressure and temperature.
What volume of 0.1 M NaOH is required to neutralize 25 cm³ of 0.2 M H₂SO₄? [1 cm³ = 0.001 dm³]
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O; moles H₂SO₄ = 0.2 × 0.025 = 0.005 mol; moles NaOH = 0.005 × 2 = 0.01 mol; volume NaOH = 0.01/0.1 = 0.1 dm³ = 100 cm³.
In the redox reaction 2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O, the reducing agent is
C₂O₄²⁻ is oxidized to CO₂, losing electrons, making it the reducing agent.
The product of the reaction between ethanol and ethanoic acid in the presence of concentrated H₂SO₄ is
Esterification produces ethyl ethanoate (CH₃COOC₂H₅) from ethanol and ethanoic acid.
The rate of a chemical reaction is increased by
Increasing reactant concentration increases collision frequency, speeding up the reaction.
Acid rain is primarily caused by the emission of
SO₂ reacts with water in the atmosphere to form H₂SO₄, contributing to acid rain.
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