Week 2 — Quiz (auto-graded) · The Chemistry of Life

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective tested: Objective 2 — atoms & chemical bonds; water's emergent properties; pH, acids, bases & buffers (including the 10×-per-unit rule).
Points: 10 (1 each) · Assignment group: Quizzes (10% of grade) · Due: end of Module 2.

This is the human-readable quiz with its vetted answer key and feedback. The import-ready Classic QTI is in F-quiz-week-02-qti.xml (generated by the shared validated script — parses with 10 items, every single-answer item exactly one correct). The reusable item-bank entries and the Canvas placement block are at the bottom of this file.

Blueprint

No trick questions; distractors target the Week 2 misconceptions named in the lecture outline. Items 5, 7, and 10 are the quantitative-pocket items — every value is pre-computed and independently re-verified (see the Quality gate).

Questions, key, and feedback

Q1 (MC). Which of the following is a molecule rather than a single atom?
- A. A single hydrogen, H
- B. Water, H₂O (two hydrogen atoms bonded to one oxygen atom) ✅
- C. A single carbon, C
- D. A single oxygen, O
Feedback: A molecule is two or more atoms bonded together, so water (H₂O) qualifies. A, C, and D are each a single atom — one building block. "An atom is a brick; a molecule is what you build from bricks."

Q2 (MC). In an ionic bond, such as the one in table salt (NaCl), what happens to the electrons?
- A. The atoms share a pair of electrons equally
- B. One atom transfers an electron to the other, creating charged ions that attract ✅
- C. The electrons are destroyed
- D. Nothing happens to the electrons at all
Feedback: Ionic bonds transfer an electron (sodium gives one to chlorine), making a + ion and a − ion that attract. Sharing a pair of electrons (A) is a covalent bond — that's the classic mix-up. Electrons are never destroyed (C).

Q3 (Multiple answer — select all that apply). Which of the following are properties of water that result from its polarity and hydrogen bonding?
- A. Cohesion (water sticks to itself), producing high surface tension ✅
- B. Water is nonpolar and cannot dissolve salts or sugars
- C. High specific heat (water resists temperature change) ✅
- D. Ice is less dense than liquid water, so it floats ✅
- E. Water repels all other substances and never sticks to surfaces
Feedback: Cohesion/surface tension, high specific heat, and floating ice all flow from water's polarity → hydrogen bonds. B is false (water is polar and is the universal solvent); E is false (water's adhesion makes it stick to surfaces, e.g., climbing a paper towel).

Q4 (MC). A water strider stands on the surface of a pond because water molecules cling tightly to each other, creating surface tension. Water sticking to itself like this is called —
- A. adhesion
- B. cohesion ✅
- C. evaporation
- D. dissolving
Feedback: Cohesion is water-to-water attraction (hydrogen bonds), which produces the surface tension the strider stands on. Adhesion (A) is water sticking to a different surface. "Co = company (water with water); Ad = add a different surface."

Q5 (MC). On the pH scale, which of the following solutions is the most acidic?
- A. pH 2 ✅
- B. pH 5
- C. pH 7
- D. pH 9
Feedback: Lower pH = more hydrogen ions = more acidic, so the lowest number (pH 2) is the most acidic. pH 7 is neutral and pH 9 is basic. "Low number, high acid." (Pre-verified: most acidic of {2, 5, 7, 9} = pH 2.)

Q6 (Matching). Match each Week 2 term to its correct meaning.
| Term | Correct meaning |
|---|---|
| Covalent bond | Atoms share a pair of electrons |
| Ionic bond | One atom transfers an electron, forming charged ions |
| Cohesion | Water molecules stick to one another |
| Adhesion | Water molecules stick to a different surface |
Feedback: The classic mix-ups: covalent = share vs. ionic = transfer; cohesion = water-to-water vs. adhesion = water-to-another-surface.

Q7 (MC). The pH scale is logarithmic: each step of 1 represents a tenfold (10×) change in hydrogen-ion concentration. How many times more acidic is a solution at pH 4 than a solution at pH 7?
- A. 3 times more acidic
- B. 7 times more acidic
- C. 100 times more acidic
- D. 1000 times more acidic ✅
Feedback: From pH 7 to pH 4 is 3 steps, and each step is ×10: 10 × 10 × 10 = 10³ = 1000×. Don't subtract the pH numbers (that gives the trap answer "3"); count the steps and raise 10 to that power. (Pre-verified: 10^(7−4) = 1000×.)

Q8 (True / False). "A solution with a higher pH (for example, pH 9) is more acidic than a solution with a lower pH (for example, pH 3)."
- True
- False ✅
Feedback: False. It's the opposite: a lower pH means more H⁺ and is more acidic; a higher pH is more basic. pH 3 is far more acidic than pH 9. "Low number, high acid."

Q9 (MC). Human blood stays near pH 7.4 even when you eat acidic or basic foods, thanks to its buffer system. Which statement best describes what a buffer does?
- A. It permanently prevents any pH change no matter how much acid or base is added
- B. It resists and minimizes pH change by absorbing extra H⁺ or OH⁻, but can be overwhelmed ✅
- C. It raises the pH to 14 to neutralize all acids
- D. It removes all water from the blood
Feedback: A buffer resists / minimizes pH change by mopping up extra H⁺ or OH⁻ — it does not prevent all change (A is the misconception) and it has a limited capacity. "Buffers soften the blow; they don't make you bulletproof."

Q10 (MC). Because [H⁺] = 10^(−pH), the hydrogen-ion concentration of a solution at pH 3 is —
- A. 1 × 10⁻³ M ✅
- B. 3 M
- C. 1 × 10⁻⁷ M
- D. 1 × 10³ M
Feedback: [H⁺] = 10^(−pH), so at pH 3 the concentration is 10⁻³ M. (pH 7 would be 10⁻⁷ M, choice C — that's neutral water, not pH 3.) (Pre-verified: 10^(−3) = 1 × 10⁻³ M.)

Answer key (quick reference)

Quality gate (self-checked): each single-answer item has exactly one correct option; the multiple-answer item lists the three true water properties (A, C, D) and requires B and E to be left unselected; the matching item pairs four terms to four distinct meanings; no item asserts a fact outside the Week 2 course definitions. This is a quantitative pocket (pH): every numeric answer (most acidic = pH 2; pH 4 vs pH 7 = 1000×; [H⁺] at pH 3 = 1 × 10⁻³ M) was re-derived by an independent Python check that printed PASS — quantitative gate: PASS (0 errors). All pH values are engineered to clean powers of ten.

Item-bank entries (for variants + the midterm/final)

All ten items are tagged course=BIOL101 · week=2 · objective=2 · topic=chemistry-of-life and deposited in Item Bank: Week 2 — The Chemistry of Life. The midterm (Week 8) and the per-term variant updates draw fresh items from this bank. (Tags: q1 atom-vs-molecule, q2 ionic-vs-covalent, q3 water-properties, q4 cohesion-vs-adhesion, q5 most-acidic-pH, q6 chemistry-terms-match, q7 ten-fold-rule, q8 higher-pH-misconception, q9 buffer-function, q10 H-ion-concentration.)

Canvas placement block

canvas_object   = Quizzes::Quiz
title           = "Week 2 Quiz — The Chemistry of Life"
assignment_group = "Quizzes"
points_possible = 10
grading_type    = points
due_offset_days = 6        # 6 days after module start
published       = true
shuffle_answers = true
provenance      = "~ Prof. Castellano's edition · Fall 2026 · built with thecoursemaker.com"