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Chem Ch 1.3-6

Syllabus, Materials, Access, and Accommodations

  • Materials are posted on the campus web page; instructor uses the textbook and a workbook-style presentation. Textbook reading is expected and aligned with course material to avoid learning conflicting content.
  • Study worksheets: summaries of lectures without answers; intended as study aids.
  • Additional materials: study sections for the exam; more resources will be posted.
  • Accessibility and accommodations: if you have SSD accommodations, contact the instructor to discuss how to accommodate needs. Emphasis on equal access to materials for all students.

Assignments and Course Logistics

  • Where to find assignments: use the course page, click Assignments, select Chapter One, then click the accept action to enable access/submission.
  • Questions about assignments: the instructor is open to addressing questions (prompt if needed).

Clicker System and Participation

  • We use a clicker system for in-class questions.
  • How to join: instructions are given for joining sections; participation is tracked via clicker responses.
  • If you have questions during this process, email or contact the instructor to get answers.

Quick Review: Context and Key Topics from Last Session

  • Previously discussed methods and chemistry.
  • The chemistry portion notes that there are 118 discovered elements arranged in the periodic table.
  • Expectation: students should learn the names and abbreviations of elements as organized in the periodic table.
  • The topic of changes in matter was introduced: distinguishing physical and chemical changes.

Physical vs Chemical Changes

  • Physical change: the composition of the matter does not change.
  • Chemical change: involves a chemical reaction with potential physical phenomena accompanying it.
  • Demonstration prompt described (with ventilation): burning a substance to illustrate a chemical change with energy release.
  • Common products and indicators of combustion: smoke, charcoal (carbon), carbon dioxide, water vapor.
  • Incomplete combustion can yield carbon-rich residues (char/soot) due to limited oxygen.
  • Role of oxidizers: some experiments use oxidizers (e.g., potassium chlorate) to accelerate combustion; in real reactions, oxidizers promote burning and energy release.
  • Key takeaway: chemical changes are characterized by new substances and possible gas evolution; physical changes do not alter composition.

Properties: Intensive vs Extensive (note: transcript uses “expensive” by mistake)

  • Extensive properties: depend on the amount of matter present (e.g., mass, volume).
  • Intensive properties: do not depend on the amount of matter (e.g., density, temperature).
  • Example: doubling the amount of tea increases the volume and mass (extensive properties).
  • Density of pure water:
    ho_{ ext{water}} = 1~ ext{g/mL} (used for calibration and comparisons).
  • Calibration principle: balances and instruments are calibrated using a known reference (pure water) to ensure accuracy.

Measurement, Uncertainty, and Error

  • Uncertainty in measurement arises from limitations in measurement processes.
  • Types of errors:
    • Systematic errors: biases that skew measurements in a particular direction (e.g., a consistently faulty scale).
    • Random errors: fluctuations due to unpredictable variations.
  • Important measurement concepts:
    • Precision: how repeatable or consistent measurements are across trials.
    • Accuracy: how close a measurement is to the true or accepted value.
    • Distinguishing the two: high precision does not guarantee high accuracy if the instrument is not properly calibrated.
  • Calibration example: water density is used to calibrate balances; accurate calibration helps ensure both precision and accuracy.

Mass, Volume, and Significant Figures

  • In chemistry, mass and volume are frequently measured quantities with associated uncertainty.
  • Significant figures: the number of meaningful digits in a measurement; used to express precision.
  • Rules (summary):
    • For multiplication and division: the result should have as many significant figures as the factor with the fewest significant figures.
    • For addition and subtraction: the result should have the same number of decimal places as the quantity with the fewest decimal places.
  • Example considerations (conceptual, not step-by-step): when multiplying several numbers, the trailing figures in the result reflect the least precise input measurement.

Example Calculations and Practice Concepts

  • Demonstration of combining significant figures in practice: when a calculation involves multiple numbers with different precision, the final answer’s precision is limited by the least precise input.
  • If a calculation expression is given as a fraction of two measured quantities, either approach (stepwise or calculator) should yield the same final value, but you must report it with the correct number of significant figures.
  • Prefix notation (SI prefixes): be familiar with common multipliers.
    • Deci: 10^{-1}, Centi: 10^{-2}, Milli: 10^{-3}, Micro: 10^{-6}, Nano: 10^{-9}, Pico: 10^{-12}
    • Kilo: 10^{3}, Mega: 10^{6}, Giga: 10^{9}, Tera: 10^{12}

SI Prefix Examples and Practical Application

  • Common use: scale measurements to appropriate magnitudes; unit conversions are essential in reporting results clearly.
  • Example: a penny mass measurement near 2.50 g demonstrates precision in a typical balance reading across trials (e.g., 2.49 g, 2.51 g).

Real-World Demo: Penny Mass Measurement

  • Student one measured a US penny across three trials: masses around 2.49 g, 2.50 g, 2.51 g; average approximately 2.5 g.
  • This illustrates how repeated measurements can yield a precise and close-to-true value, and is used to discuss measurement uncertainty and calibration.

Practical Calculation: Hydrogen Peroxide in a 5% Solution

  • Scenario: determine the mass of H₂O₂ in a given solution mass fraction.
  • Definition: percent by mass is given by
    • ext{wt ext%} = rac{m{ ext{solute}}}{m{ ext{solution}}} imes 100 ext{%}
  • For a solution with density near 1 g/mL, a mass-based calculation is:
    • If you have 20 g of solution with 5% H₂O₂ by mass, then
    • m_{ ext{H₂O₂}} = 0.05 imes 20~ ext{g} = 1.0~ ext{g}
    • Volume of this portion (approximate, using density ρ ≈ 1 g/mL):
    • V ext{ of } ext{H₂O₂ solution} ext{ ~ } rac{m}{
      ho} ext{ }
      ightarrow ext{ ~ } 20~ ext{mL} / 1 ext{ g/mL} ext{ (for the whole solution)}
  • Practical takeaway: in a 20 g sample of a 5% solution, there is about 1 g of H₂O₂; the exact volume depends on density, which can be looked up and used for conversion to mL.

Classroom Roles and Demos Mentioned

  • Kyle: student or TA who performs a demo related to the review topic (chemistry demonstration).
  • Owen: mentioned as performing a safety-related action (ventilation) during the combustion demonstration.
  • Thematic emphasis: use of demonstrations to illustrate chemical changes and measurement concepts.

Connections to Foundational Principles and Real-World Relevance

  • Alignment with foundational ideas in chemistry: measuring properties, reporting with appropriate significant figures, understanding uncertainty, and recognizing the difference between physical and chemical changes.
  • Real-world relevance: calibration practices (using water density), precision vs accuracy in instrumentation, and quantitative reasoning for solutions and concentrations.
  • Ethical/practical implications: ensuring equal access to course materials and accommodations; inclusive teaching practices to support all students.

Quick Reference Formulas and Concepts (LaTeX)

  • Density:
    ho = rac{m}{V}
  • Mass of solute in a solution: m{ ext{solute}} = ext{mass}{ ext{solution}} imes rac{ ext{wt ext%}}{100}
  • Mass percent definition: ext{wt ext%} = rac{m{ ext{solute}}}{m{ ext{solution}}} imes 100 ext%
  • Significant figures rules (summary):
    • Multiplication/Division: the result has as many SF as the input with the fewest SF.
    • Addition/Subtraction: the result should have the same number of decimal places as the input with the fewest decimal places.
  • Common SI prefixes (examples):
    • ext{deci} = 10^{-1}, ext{centi} = 10^{-2}, ext{milli} = 10^{-3}, ext{micro} = 10^{-6}, ext{nano} = 10^{-9}, ext{pico} = 10^{-12}
    • ext{kilo} = 10^{3}, ext{mega} = 10^{6}, ext{giga} = 10^{9}, ext{tera} = 10^{12}

Note to self for future sessions

  • Some phrases in the transcript were misheard (e.g., “expensive” instead of “extensive,” and “laminates” likely should be “lanthanides” or a stray mis-transcription). When reviewing with students, clarify these terms from authoritative sources.
  • Emphasize the practical implications of accuracy, precision, and calibration in real experiments.