Chapter_2_Review_Questions

Review Questions – Chapter 2

Question 1

• Postulate of Dalton’s Theory: Consistent with the Law of Conservation of Mass.

• Observation: Heating 100 grams of solid calcium carbonate produces 44 grams of carbon dioxide and 56 grams of calcium oxide.

• Explanation: Total mass of reactants (100 g) equals total mass of products (44 g + 56 g = 100 g).

Question 2

• Postulate Violated: Dalton's postulate states that all atoms of a given element are identical in mass and properties.

• Observation: Two samples of titanium dioxide show different percentages of titanium (59.95% and 60.10%).

• Explanation: This variation implies that the titanium in those samples has different isotopic compositions or mixtures, thus violating the postulate.

Question 3

• Observation: Iron nail corroding forms rust (Iron (III) oxide).

  • (a) Expectation for Mass Change: Mass increases after rust formation.

    • Explanation: Iron combines with oxygen, gaining mass from the added oxygen.

  • (b) Mass Calculation:

    • Final mass = 24.1 g, initial mass = 23.2 g.

    • Mass gained = 24.1 g - 23.2 g = 0.9 g (mass of oxygen combined).

Question 4

• Fermentation process: Yeast converts glucose to ethanol and carbon dioxide.

  • (a) Total Mass of Products: If 200.0 g of glucose is fully converted, the mass of ethanol and carbon dioxide remains 200.0 g.

  • (b) Expectation for Mass Change in Open Container: Mass would be less after fermentation.

    • Explanation: CO2 escapes into the atmosphere, reducing total mass.

  • (c) Mass of Ethanol Calculation:

    • If 97.7 g of CO2 is produced, the mass of ethanol = 200.0 g - 97.7 g = 102.3 g.

Question 5

• Ion Symbol Writing:

  • (a) Ion with 1+ charge, atomic number 55, mass number 133: Cs⁺ (Cesium)

  • (b) Ion with 54 electrons, 53 protons, 74 neutrons: I⁻ (Iodine)

  • (c) Ion with atomic number 15, mass number 31, 3− charge: P³⁻ (Phosphide)

  • (d) Ion with 24 electrons, 30 neutrons, 3+ charge: Cr³⁺ (Chromium)

Question 6

• Protons, Electrons, Neutrons in Isotopes:

  • (a) Boron-10: 5 protons, 5 electrons, 5 neutrons.

  • (b) Mercury-199: 80 protons, 80 electrons, 119 neutrons.

  • (c) Copper-63: 29 protons, 29 electrons, 34 neutrons.

  • (d) Carbon-13: 6 protons, 6 electrons, 7 neutrons.

  • (e) Selenium-77: 34 protons, 34 electrons, 43 neutrons.

Question 7

• Element's Natural Abundances and Isotopic Masses:

  • Abundances/Isotopic masses:

    • 90.92% at 19.99 amu

    • 0.26% at 20.99 amu

    • 8.82% at 21.99 amu

  • Average atomic mass calculation = (0.9092 * 19.99) + (0.0026 * 20.99) + (0.0882 * 21.99)

Question 8

• Average Atomic Mass of Bromine:

  • Isotopes: 79Br (mass: 78.9183, abundance: 50.69%) and 81Br (mass: 80.9163, abundance: 49.31%).

  • Calculation:

    • Average atomic mass = (0.5069 * 78.9183) + (0.4931 * 80.9163)

Question 9

• Average Atomic Mass of Lithium Sources:

  • Natural Composition: 7.5% for 6Li (6.01512 amu) and 92.5% for 7Li (7.01600 amu).

  • Commercial Source: 3.75% for 6Li (with the rest as 7Li).

  • Calculations for both sources regarding average atomic mass.

Question 10

• Variations in Average Atomic Mass of Boron:

  • Isotopes: 10B (10.0129 amu) and 11B (11.0931 amu).

  • Percent Abundance Calculations:

    • Calculate abundances leading to average atomic masses of 10.807 and 10.819.

Question 11

• Oxygen Isotopes in Meteorites:

  • Observation: 18O:16O abundance ratio is greater in meteorites than on Earth.

  • Conclusion: Average mass of oxygen atoms in meteorites is greater than that of terrestrial oxygen atoms.