Which of the following gases can be collected by the upward displacement of air?
Ammonia (NH₃, molar mass 17) is lighter than air (molar mass ~29), collected by upward displacement.
The oxide that remains unchanged when heated in hydrogen is
Fe₂O₃ resists reduction by hydrogen under standard conditions; CuO, PbO, ZnO reduce to metals.
What is the change in oxidation number of sulfur in the reaction: S + O₂ → SO₂?
Sulfur: 0 in S, +4 in SO₂ (O = -2, 2 × -2 = -4, so S = +4). Change is 0 to +4.
A reaction characteristic of an unsaturated hydrocarbon is
Unsaturated hydrocarbons (e.g., alkenes) undergo addition reactions due to double/triple bonds.
For the reaction 2X + Y → Z, the rate of formation of Z is independent of the concentration of Y and quadruples when the concentration of X is doubled. The rate equation is
Independent of [Y] (order 0), quadruples when [X] doubles (order 2). Rate = k[X]².
For the reaction 2X + Y ⇌ Z, exothermic in the forward direction, a decrease in temperature will
Exothermic forward reaction is favored by lower temperature (Le Chatelier’s principle).
Pure metals are often used in electrical wiring because
Pure metals (e.g., copper) are ductile, drawn into wires, and highly conductive.
The structural formula of 2-methylbutan-2-ol is
2-methylbutan-2-ol is (CH₃)₃COH, a tertiary alcohol with —OH on the second carbon.
Dehydration of CH₃CH₂CH₂CH₂OH gives
Butan-1-ol (CH₃CH₂CH₂CH₂OH) dehydrates to but-1-ene (CH₂=CHCH₂CH₃).
Which of the following is a primary alcohol?
CH₃CH₂OH (ethanol) is primary (—OH on carbon with one other carbon).
The product of the reaction between ethanoic acid and ethanol in the presence of concentrated H₂SO₄ is
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ (ethyl ethanoate) + H₂O.
The IUPAC name of CH₃CH₂COOH is
CH₃CH₂COOH (three carbons) is propanoic acid.
Which of the following is a secondary amine?
(CH₃)₂NH is a secondary amine (R₂NH). Others are primary or tertiary.
The reaction of ethene with bromine water produces
C₂H₄ + Br₂ → C₂H₄Br₂ (1,2-dibromoethane).
The functional group present in CH₃COCH₃ is
CH₃COCH₃ (propanone) has a ketone group (C=O with two alkyl groups).
The product of the complete combustion of methane (CH₄) in oxygen is
CH₄ + 2O₂ → CO₂ + 2H₂O (complete combustion).
Which of the following is NOT a property of an ideal gas?
Ideal gases have no intermolecular attractions.
The compound formed when ethanol is heated with concentrated H₂SO₄ at 180°C is
C₂H₅OH → C₂H₄ + H₂O (dehydration to ethene).
The oxidation number of sulphur in H₂SO₄ is
H = +1, O = -2. 2(+1) + S + 4(-2) = 0 → S = +6.
What is the product when copper(II) sulfate is electrolyzed using copper electrodes?
Cu²⁺ + 2e⁻ → Cu (cathode); Cu → Cu²⁺ + 2e⁻ (anode).
For the reaction 2H₂(g) + O₂(g) → 2H₂O(l), ΔH = -572 kJ. What is the enthalpy change for the formation of 1 mole of H₂O?
ΔH = -572 kJ for 2 moles H₂O. For 1 mole: -572/2 = -286 kJ.
What is the activation energy in a reaction?
Activation energy is the minimum energy needed to initiate a reaction.
What is the atomic number of an element with 2 protons and 2 neutrons?
Atomic number = number of protons = 2 (helium).
What gas is produced when copper(II) sulfate reacts with iron?
Fe + CuSO₄ → FeSO₄ + Cu (displacement, no gas).
Clothes should be properly rinsed with water after bleaching because?
Chlorine can damage fabrics if not rinsed off.
Which of these metals CANNOT replace hydrogen from alkaline solutions?
Iron, below hydrogen in reactivity series, cannot displace hydrogen.
The relatively high boiling point of alkanol is due to?
Alkanols have high boiling points due to hydrogen bonding.
What is the product of the reaction between calcium carbonate and dilute hydrochloric acid?
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
What is the pH at the equivalence point of a titration between HCl and NaOH?
Strong acid (HCl) + strong base (NaOH) yields neutral pH 7 at equivalence.
Which of the following processes involves a decrease in entropy?
Condensation (gas to liquid) decreases entropy by reducing disorder.
What is the effect of increasing pressure on the equilibrium of the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
Increasing pressure favors fewer gas moles (4 to 2), shifting equilibrium right.
A mixture of 0.20 mole of Ar, 0.20 mole of N₂, and 0.30 mole of He exerts a total pressure of 2.1 atm. The partial pressure of He is
Total moles = 0.70. He mole fraction = 0.30/0.70 = 3/7. Partial pressure = (3/7) × 2.1 = 0.9 atm.
Which pair of elements has the same chemical properties?
Na and K (Group 1) share similar properties due to one valence electron.
In the periodic table, what is the property that decreases along a period and increases down a group?
Atomic radius decreases across a period (increased nuclear charge), increases down a group (more shells).
Oxygen is a mixture of two isotopes, ¹⁶O and ¹⁸O, with a relative abundance of 90% and 10% respectively. The relative atomic mass of oxygen is
(0.9 × 16) + (0.1 × 18) = 14.4 + 1.8 = 16.2.
Which of the following pollutants is the most dangerous?
Carbon(II) oxide (CO) is highly toxic, binding to hemoglobin, causing suffocation.
The hydroxide ion concentration, [OH⁻], in a solution of sodium hydroxide with pH 10.0 is
pH = 10 → pOH = 14 - 10 = 4 → [OH⁻] = 10⁻⁴ mol dm⁻³.
When platinum electrodes are used during the electrolysis of copper(II) tetraoxosulphate(IV) solution, the solution becomes progressively
Anode produces H⁺ (2H₂O → O₂ + 4H⁺ + 4e⁻), making the solution acidic.
What is the oxidation number of Zn in ZnCl₂?
Cl = -1. Zn + 2(-1) = 0 → Zn = +2.
The reaction that is accompanied by a decrease in entropy when carried out at constant temperature is
N₂ + 3H₂ → 2NH₃ reduces gas moles (4 to 2), decreasing entropy.
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