Chemistry 1100 Exam Notes

Personal Performance Assessment #2

Professor: Keller
Date: 3 October 2024
Important Conversion Factors:
- 1 kg = 1000 g
- 1 mol = 6.02 x 10²³ atoms

Multiple Choice Section

When CO2 molecules absorb infrared radiation:
- (A) their velocity doubles.
- (B) they rotate faster.
- (C) their covalent bonds break.
- (D) they vibrate more.
Why are atomic masses in the periodic table not exact integers?
- (A) Our technology does not allow for exact measurement of such a small quantity.
- (B) Atoms gain and lose electrons easily and that changes their masses significantly.
- (C) Atomic masses listed in the periodic table are weighted averages of isotopic masses.
- (D) Atomic masses are measured in real samples that are always contaminated with other elements.
Which molecule has a tetrahedral molecular geometry?
- (A) CO2
- (B) NH3
- (C) O3
- (D) CH2F2
- (E) none of them.
CO2 emissions from fossil fuels have totaled about 120 billion tons over the past 20 years. However, only about 80 billion tons have accumulated in the atmosphere. Why?
- (A) Much of the emitted CO2 has escaped into space.
- (B) The oceans have absorbed about one-third of the emitted CO2.
- (C) Absorption of infrared radiation from the Sun has broken apart many CO2 molecules into CO and O.
- (D) The extra recent CO2 was buried deep in the ice in Antarctica.
The octet rule applied to bonding in carbon-containing compounds states:
- (A) each carbon atom must make 4 single bonds to other atoms.
- (B) each bonded carbon atom forms eight bonds.
- (C) all carbon-containing compounds contain at least eight bonds.
- (D) the number of atoms in any carbon-containing compound is a multiple of eight.
- (E) each carbon atom forms bonds so as to have 8 electrons around it.
What is the relationship between stratospheric levels of atomic chlorine and ozone?
- (A) As chlorine increases, ozone increases.
- (B) As chlorine increases, ozone decreases.
- (C) As chlorine changes, the effect on the ozone level is unpredictable.
- (D) As chlorine changes, there is no effect on the ozone level.
Which figure best depicts the greenhouse effect? (Illustration choices not provided)
- Possible choices included solar energy interactions with Earth and atmospheric gases.
Which processes add carbon, in the form of carbon dioxide, to the atmosphere?
- I. Respiration of humans and animals
- II. Deforestation by cutting and burning trees
- III. Photosynthesis
- IV. Combustion of fossil fuels
- (A) I and IV only
- (B) II and IV only
- (C) I, II, and IV only
- (D) II, III, and IV only
Breaking chemical bonds:
- (A) costs energy.
- (B) releases energy.
How many atoms are in one mole of CH3OH?
- (A) 6
- (B) 6.0 x 10²³
- (C) 12.0 x 10²³
- (D) 3.6 x 10²⁴
- (E) 3

Short Answer Section

An average grain of salt (NaCl) weighs 6.48 x 10⁻⁵ kg. How many chloride ions are in one grain of salt?
- Calculation:
  - (6.48 imes 10^{-5} ext{ kg}) imes (1000 ext{ g/kg}) = 6.48 imes 10^{-2} ext{ g NaCl}
  - (6.48 imes 10^{-2} ext{ g NaCl}) / (58.4 ext{ g/mol}) = 1.11 imes 10^{-3} ext{ mol NaCl}
  - 1.11 imes 10^{-3} ext{ mol NaCl} imes (6.02 imes 10^{23} ext{ ions/mol}) = 6.68 imes 10^{20} ext{ ions}
Diimide (HNNH) Analysis:
- (a) Lewis structure includes all lone pairs:
  - H-N=NH
- (b) Molecular structure:
  - H-N=N-H or H-N≡N-H
- (c) Is Diimide a greenhouse gas?
  - Yes.
  - Explanation: Diimide has three bonds, which means it can stretch and bend (vibrate) in response to absorbing infrared radiation.
Combustion of Jet Fuel:
- Chemical Reaction:
  - C{12}H{23} + 17 O2 ightarrow 12 CO2 + rac{23}{2} H_2O
- Estimate: 2.05 x 10¹¹ grams of jet fuel per school per year.
- To calculate CO2 released:
  - (2.05 imes 10^{11} ext{ g C}{12}H{23}) imes rac{1 ext{ mol C}{12}H{23}}{1679 ext{ g C}{12}H{23}} imes rac{12 ext{ mol CO}2}{1 ext{ mol C}{12}H{23}} imes rac{44 ext{ g CO}2}{1 ext{ mol CO}2} = 6.48 imes 10^{12} ext{ grams CO}2
Steven Chu's Proposal:
- Proposal: Painting roofs white and using light-colored pavement to reduce global warming.
- Reasoning:
  - Increase the albedo of Earth's surface which reflects more incoming radiation, leading to a cooling effect, and potential energy savings by keeping buildings cooler.
Potential Consequences of Global Warming/Climate Change:
- Sea-level rise
- More extreme weather
- Ocean acidification
- Freshwater stresses
- (Each consequence classified for 3 points)
Reactions in the Stratosphere:
- (a) Overall Reactions:
  - Pair A: O_2 + UV
    ightarrow 2O
  - Pair B: O + O2 ightarrow O3
- (b) Which pair corresponds to ozone formation?: Circle Pair B.
- (c) Which UV photon has the shortest wavelength?: Circle photon in Pair A.