A gas sample with an initial volume of 32.5 dm³ is heated and expands to 975 dm³ at constant pressure. What is the ratio of the final absolute temperature to the initial absolute temperature?
By Charles’ law (V/T = constant at constant pressure), V₁/T₁ = V₂/T₂. Given V₁ = 32.5 dm³, V₂ = 975 dm³, T₂/T₁ = V₂/V₁ = 975/32.5 = 30. Thus, the ratio is 30:1. [Note: Original answer B (3:1) was incorrect; corrected to A.]
Two cylinders A and B contain 50 cm³ of oxygen and nitrogen, respectively, at the same temperature and pressure. If cylinder A has 5.0 moles of oxygen, how many moles of nitrogen are in cylinder B?
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain the same number of moles. Thus, 50 cm³ of nitrogen in B has the same 5.0 moles as oxygen in A.
When does a liquid begin to boil?
A liquid boils when its vapour pressure equals the atmospheric pressure, allowing vapour bubbles to form within the liquid.
A particle with 8 protons, 9 neutrons, and 7 electrons is represented as?
With 8 protons, the element is oxygen (O). Mass number = 8 + 9 = 17. With 7 electrons (1 less than protons), it has a +1 charge, so it is ¹⁷O⁺.
Using the periodic table section below, which letters indicate an alkali metal and a noble gas, respectively?
| | G | X | | J | E | | | L |
| I | | 5 | 6 | 7 | | | 10 | 11 |
| U | M | R | 14 | 15 | | 17 | 18 |
Alkali metals are in Group 1 (G), and noble gases are in Group 18 (L). Thus, G and L represent an alkali metal and a noble gas.
Using the periodic table section above, which element can form a covalent compound?
Covalent compounds form between non-metals. R (likely Group 14, e.g., carbon) is a non-metal and can form covalent compounds, unlike G (alkali metal), M (likely metal), or L (noble gas).
Which letter in the periodic table section represents a non-metal that is solid at room temperature?
Non-metals solid at room temperature include carbon (Group 14). R, likely carbon, fits this description. [Note: T is not in the table, but C is correct based on context.]
What did Millikan determine in his oil drop experiment?
Millikan’s oil drop experiment measured the charge of the electron by balancing gravitational and electric forces on charged oil droplets.
The stability of ionic solids is primarily due to?
Lattice energy, the energy released when gaseous ions form a solid lattice, stabilizes ionic solids.
Which statement is false about isotopes of the same element?
Isotopes have the same number of protons and electrons (in neutral atoms) but different numbers of neutrons, so D is false.
Why is helium used in observation balloons?
Helium is lighter than air and non-combustible, making it safe for balloons, unlike hydrogen.
Burning chloromethane-based plastics in the open releases which gas?
Burning chloromethane (CH₃Cl) releases hydrogen chloride (HCl) due to the presence of chlorine.
Deliquescent substances are also?
Deliquescent substances absorb water and dissolve in it, a trait shared with hygroscopic substances, though deliquescence is more extreme.
How do colloids differ from suspensions?
Colloids scatter light (Tyndall effect) and do not settle, while suspensions settle over time and may not scatter light as effectively.
Why does solubility of most solutes in water increase with temperature?
Most solids’ dissolution in water is endothermic, so increasing temperature favors solubility by providing energy to break solute bonds.
Which solution has a pH less than 7?
NH₄Cl, from a weak base (NH₃) and strong acid (HCl), forms an acidic solution (pH < 7) due to NH₄⁺ hydrolysis.
What is the pH of a 2.0 × 10⁻³ M solution of sodium hydroxide?
NaOH is a strong base, so [OH⁻] = 2.0 × 10⁻³ M. pOH = -log(2.0 × 10⁻³) ≈ 2.7. pH = 14 - 2.7 = 11.3.
In silver-plating a metal M, the metal M is the?
In silver-plating, metal M is the cathode, where Ag⁺ ions are reduced to deposit silver.
How many moles of copper are deposited by passing 3F of electricity through a copper(II) sulphate solution? [F = 96500 C mol⁻¹]
Cu²⁺ + 2e⁻ → Cu. 2F deposits 1 mole of Cu. Thus, 3F deposits 3/2 = 1.5 moles.
The reaction Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g) illustrates?
Fe is oxidized to Fe²⁺, and H⁺ is reduced to H₂, indicating a redox reaction.
Which reaction is a redox reaction?
Fe + 2HCl → FeCl₂ + H₂ involves oxidation of Fe (0 to +2) and reduction of H⁺ to H₂, a redox reaction.
For an equilibrium reaction with ΔH < 0, the forward reaction is favored at?
For an exothermic reaction (ΔH < 0), low temperatures favor the forward reaction per Le Chatelier’s principle, as heat is a product.
Which process increases entropy?
Mixing NaCl and sand increases disorder (entropy). The other processes increase order, decreasing entropy.
Which gas turns orange potassium dichromate solution to green?
Sulfur(IV) oxide (SO₂) reduces orange dichromate (Cr₂O₇²⁻) to green chromium(III) ions (Cr³⁺).
What are the products when sodium reacts with ethanol?
Sodium reacts with ethanol to form sodium ethoxide (C₂H₅ONa) and hydrogen: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂.
What is the general formula of alkanones?
Alkanones (ketones) have the formula RCOR, with a carbonyl group (C=O).
Sulphur’s six solid-state forms are an example of?
Allotropy is when an element exists in multiple physical forms in the same state, like sulphur’s rhombic and monoclinic forms.
How are aromatic and aliphatic hydrocarbons distinguished?
Aliphatic hydrocarbons (e.g., alkenes) decolorize bromine water via addition, while aromatic hydrocarbons (e.g., benzene) undergo substitution, not decolorizing bromine.
What is the role of sodium chloride in soap preparation?
Sodium chloride 'salts out' soap, reducing its solubility to separate it from glycerol and the aqueous solution.
What is the functional group in ethanol?
Ethanol (C₂H₅OH) is an alkanol (alcohol) with the -OH functional group.
In the reaction C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, the hydrocarbon C₃H₈ is?
C₃H₈ is an alkane with 3 carbons, propane. The reaction is combustion, producing CO₂ and H₂O.
Which orbitals of carbon are hybridized in methanol?
In methanol (CH₃OH), carbon is sp³ hybridized, mixing one 2s and three 2p orbitals to form four sp³ orbitals.
What type of reaction occurs when ethene reacts with bromine water?
Ethene (C₂H₄) undergoes an addition reaction with bromine water, forming 1,2-dibromoethane by breaking its double bond.
Why is sodium hydroxide used in preparing ethene from ethanol?
Sodium hydroxide absorbs CO₂ impurities during ethene preparation, purifying the gas.
Which hydrocarbon gives a white precipitate with aqueous NaOH and is soluble in excess NaOH?
Hydrocarbons like methane, ethane, and propane are non-polar and do not react with NaOH to form precipitates or dissolve.
How does a catalyst affect a reaction’s activation energy?
A catalyst lowers activation energy by providing an alternative reaction pathway, increasing the reaction rate.
Which factor increases the rate of a chemical reaction?
Increasing reactant concentration increases collision frequency, thus increasing the reaction rate.
In hydrogen production from natural gas, how is carbon(IV) oxide removed?
CO₂ is removed by washing under pressure with water or a solvent (e.g., potassium carbonate), which absorbs CO₂.
What is the functional group in propanol?
Propanol (C₃H₇OH) is an alcohol with the -OH (hydroxyl) functional group.
Which ion forms a white precipitate with aqueous NaOH that dissolves in excess NaOH?
Zn²⁺ forms Zn(OH)₂ precipitate with NaOH, which dissolves in excess to form [Zn(OH)₄]²⁻. Ca²⁺ and Mg²⁺ precipitates do not dissolve, and Cu²⁺ forms a blue precipitate.
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