Comprehensive Study Notes: Scientific Measurement (Week 2)

WEEK 2

CHEMISTRY 1

SCIENTIFIC MEASUREMENT

• Focus: Understanding measurements, units, accuracy, precision, and related concepts used in chemistry and physics.

REVIEW: EXPRESSIONS OF MEASUREMENTS

• Measurements are expressed in scientific notation.
• Significance and use of significant figures.
• Two systems of measurement: Metric System (SI) and English System.

REVIEW: TYPES OF MEASUREMENTS

• Measurements can be:
  • accurate
  • precise
  • directly measured
  • derived

DIRECTLY MEASURED QUANTITIES

• Directly measured examples include: mass, volume, length, temperature.

WEIGHT AND GRAVITY

• Relationship: MASS multiplied by acceleration due to gravity gives WEIGHT.
• Formula: $\text{weight} = m \times g$
• Gravity on Earth: $g \approx 9.8\ \mathrm{m/s^2}$
• Example sketch (velocity under gravity from rest):
  • t = 0 s, v = 0 m/s
  • t = 1 s, v = 9.8 m/s
  • t = 2 s, v = 19.6 m/s
  • t = 3 s, v = 29.4 m/s
  • t = 4 s, v = 39.2 m/s
  • (Note: transcript shows typos in some values; the correct relation under constant gravity is v = g t.)

EXAMPLE PDST: WEIGHT ON DIFFERENT BODIES

• PDST: W = mg (Weight = mass × acceleration due to gravity)
• Jane’s mass: 58 kg
• Gravitational accelerations (g) used in example:
  • Earth: $g = 9.8\ \mathrm{m/s^2}$
  • Moon: $g = 1.6\ \mathrm{m/s^2}$
  • Mars: $g = 3.71\ \mathrm{m/s^2}$
  • Jupiter: $g = 25.95\ \mathrm{m/s^2}$
  • Sun: $g = 274.13\ \mathrm{m/s^2}$
• Weights (calculated as W = m g):
  • Earth:
    $W = 58 \times 9.8 = 568.4\ \text{N}$
  • Moon:
    $W = 58 \times 1.6 = 92.8\ \text{N}$
  • Mars:
    $W = 58 \times 3.71 = 215.18\ \text{N}$
  • Jupiter:
    $W = 58 \times 25.95 = 1505.1\ \text{N}$
  • Sun:
    $W = 58 \times 274.13 = 15899.54\ \text{N}$
  • (Units: newtons, N)

DERIVED QUANTITIES: DENSITY AND SPECIFIC GRAVITY

• DENSITY tells us how heavy something is for its size.

• Definition: $\rho = \frac{m}{V}$ where $\rho$ is density, $m$ is mass, and $V$ is volume.

• Example: If a rock has mass $m = 200\ g$ and volume $V = 100\ mL$, then $\rho = \frac{200\ g}{100\ mL} = 2\ g/mL$.

• SPECIFIC GRAVITY compares density to the density of water (at room temperature, water density is 1 g/mL).

• Definition: $\text{SG} = \frac{\rho}{\rho_{water}}$

• Since $\rho_{water} = 1\ g/mL$ at room temp, a liquid with density 1.2 g/mL has SG = 1.2 (no units).

LENGTH, TEMPERATURE, MASS, VOLUME: UNIT CONVERSIONS

• Length conversions (as listed):
  • $1\ m = 3.3\ ft$
  • $1\ in = 2.43\ cm$
  • $1\ mi = 1.61\ km$
• Temperature conversions:
  • $°F = \frac{9}{5} (°C) + 32$
  • $°C = \frac{5}{9} (°F - 32)$
  • $K = °C + 273.15$
  • $K = \frac{5}{9} (°F - 32) + 273$
• Mass conversions:
  • $1\ kg = 2.2\ lb$
  • $1\ oz = 28.35\ g$
  • $1\ ft = 0.028\ m$ (note: transcript shows 0.028 m; standard value is 0.3048 m – this appears to be a transcription error.)
• Volume conversions:
  • $1\ mL = 1\ cm^3$
  • $1\ cup = 237\ mL$
  • $1\ gal = 16\ cups$
  • $1\ L = 1000\ mL$
  • $1\ qt = 946\ mL$
  • $1\ L = 1\ L$
• Length, area, and volume conversions include: $1\ m^3 = 35.31\ ft^3$
• Pressure conversions:
  • $1\ atm = 101.3\ kPa$
  • $1\ atm = 760\ mm\ Hg$
  • $1\ bar = 10^5\ Pa$ (transcript lists 105 Pa; standard value is 10^5 Pa)
  • $1\ psi = 68.948\ mbar$
• Energy conversions:
  • $1\ J = 2.39 \times 10^{-4}\ kcal$
  • $1\ eV = 1.602 \times 10^{-19}\ J$

SI BASE UNITS AND FOUNDATIONS

• The metric system (SI) is commonly used for length, volume, and mass.
• SI uses decimalization and prefixes to form new units.

SI BASE UNITS (BASE QUANTITIES)

• Length: $\text{Meter} \quad m$
• Mass: $\text{Kilogram} \quad kg$
• Time: $\text{Second} \quad s$
• Electric current: $\text{Ampere} \quad A$
• Temperature: $\text{Kelvin} \quad K$
• Amount of substance: $\text{Mole} \quad mol$
• Luminous intensity: $\text{Candela} \quad cd$

ENGLISH SYSTEM OVERVIEW

• The English system (US usage) includes units such as ounce (oz), pound (lb), inch (in), mile (mi), quart (qt).

KEY CONCEPT: ACCURACY AND PRECISION

• Accuracy: how close a measurement is to the true value.
• Precision: how close repeated measurements are to each other.
• When recording data, always include the numeric value, the unit, and the substance name to avoid mistakes.
• Both accuracy and precision are desirable in experiments; strive for measurements that are both.

PRACTICAL ILLUSTRATIONS OF ACCURACY & PRECISION

• Fig. A: Darts far from bull’s-eye and from each other — not accurate, not precise.
• Fig. B: Darts near each other but far from bull’s-eye — precise but not accurate.
• Fig. C: Darts close to bull’s-eye and to each other — accurate and precise.

EXPERIMENTAL EXAMPLES: ACCURACY AND PRECISION

• Example: True volume = $50.0\ mL$
  • Accurate and precise: measurements could be $49.9\ mL,\ 50.0\ mL,\ 50.1\ mL$
  • Precise but not accurate: $45.0\ mL,\ 45.1\ mL,\ 44.9\ mL$
  • Neither accurate nor precise: $40.0\ mL,\ 55.0\ mL,\ 47.5\ mL$
• Repeating trials checks precision; comparing to the true value checks accuracy.

SCITRIVIA: JULIAN BANZON

• Dr. Julian Banzon was a Filipino biophysical chemist.
• Studied making fuel from local crops like sugarcane and coconut.
• Pioneered production of ethyl esters from these plants (biofuels).
• Developed a method to extract leftover coconut oil using chemicals (not just physical methods).

IMPACT ON SOCIETY

• The inventions and discoveries influenced multiple industries, including food and chemical commodities, with a focus on biofuels.
• His work leveraged coconuts to help alleviate food shortages and starvation in the Philippines.
• His contributions opened avenues for ongoing local and international research.
• Significance: addressed pressing issues relevant today and provided a model for sustainable biofuel research.