unit 1 review research chem

Lab Equipment and Tools

• Beaker- Uses: Mixing, stirring, storing, and heating liquids.

  • Not recommended for precise measurement of volume.

• Graduated Cylinder- Used to accurately measure liquid volumes; more precise markings than a beaker.

• Erlenmeyer Flask- Conical shape facilitates swirling without spilling; narrow neck minimizes evaporation during heating.

• Test Tube- Holds small amounts of substances for testing; no measurement markings; used for small-scale reactions; always pointed away from you and others.

• Bunsen Burner- Heating, sterilizing, and combustion; provides a controllable open flame.

• Transfer Pipet- Transfers small quantities of liquid; comes in various types (micropipette, graduated pipette) for precise volumes.

• Safety Goggles- MUST be worn during ALL labs; protects eyes from chemicals, flames, and debris.

• Hot Plate- Heats substances; two main parts: Heating element and magnetic stirrer.

• Ring Stand- Used to hold equipment in place during experiments.

• Watch Glass- Used as a surface to evaporate liquids, weigh solids, heat substances, or cover glassware to prevent contamination.

Accuracy & Precision

• Accuracy: How close a measurement is to the true or accepted value.

• Precision: How close two or more measurements are to each other.

• Conceptual difference: Accuracy relates to bias (closeness to true value); precision relates to variability (reproducibility).

• Visual cues: A set of measurements can be accurate but not precise, precise but not accurate, both, or neither.

• Practical note: In chemistry, rounding and measurement reporting follow sig figs and decimal-place rules to reflect reliability.

Significant Figures (SigFig)

• Definition: Significant figures are digits that carry meaning about precision of a measurement.

• Purpose: Ensure consistency in measurements across experiments.

• Rules for counting sigfigs:

  1) Non-zero digits are always significant.

  2) Zeros between non-zero digits are significant.

  3) Leading zeros are not significant.

  4) Trailing zeros after a decimal point are significant.

  5) Trailing zeros in a whole number are not significant unless a decimal point is shown.

• Examples:

  • 46 has 2 sig figs.

  • 10005 has 5 sig figs.

  • 0.00375 has 3 sig figs (leading zeros not significant).

  • 3.75000 has 6 sig figs (trailing zeros after decimal are significant).

  • 375000 has 3 sig figs (trailing zeros in a whole number are not significant unless indicated).

• Pacific-Atlantic Rule (sigfig hack):

  • If a decimal is present, start counting from the Pacific (left) side.

  • If a decimal is absent, start counting from the Atlantic (right) side.

  • Start at the first non-zero digit and count every following digit.

• Addition and subtraction with sig figs:

  • The result should have the same number of decimal places as the measurement with the fewest decimal places.

  • Rounding practice emphasized: We ROUND in Chemistry.

• Multiplication and division with sig figs:

  • The result should have the same number of sig figs as the measurement with the fewest sig figs.

Accuracy, Precision, and Linear Thinking

• Definitions recap (for quick reference):- Accuracy: How close the measured value is to the true value.

  • Precision: How close repeated measurements are to each other.

• Visual representations: A set of data can be accurate, precise, both, or neither depending on bias and spread.

Density

• Definition: Density is the ratio of mass to volume.

• Formula: $D = \frac{m}{V}$ where mass is typically in grams (g) and volume in milliliters (mL) or liters (L).

• Mass measurement: Use a balance or scale.

• Volume measurement: Use a graduated cylinder for liquids; for irregular solids, use water displacement.

• Water displacement method:

  • When an irregular object is submerged in water, the volume of water displaced equals the volume of the object.

  • Formula to find object volume: $V<em>{\text{object}} = (V</em>{\text{water+object}}) - V_{\text{water}}$

• Example density calculations using given fluids (illustrative values from the unit):

  • Water: density (\approx 1.00 \frac{\text{g}}{\text{mL}})

  • Mercury: density (\approx 13.55 \frac{\text{g}}{\text{mL}})

  • Glycerol: density (\approx 1.26 \frac{\text{g}}{\text{mL}})

  • Ethanol: density (\approx 0.79 \frac{\text{g}}{\text{mL}})

  • Oil: density (\approx 0.90 \frac{\text{g}}{\text{mL}})

  • Seawater: density (\approx 1.03 \frac{\text{g}}{\text{mL}})

• Practical density tasks (scenarios):

  • If mass and volume are known, compute density directly with $D = \frac{m}{V}$.

  • Density units commonly used: g/mL or g/cm^3 (1 g/mL = 1 g/cm^3).