PLD-Experiment-No. 1

Experiment No. 1: Measurements with Statistics

Overview

  • Presented by: GOLEZ Chem & Phys

  • Focus: Understanding basic measurements in analytical chemistry.

  • Statistical concepts relevant to experiments are explored.

Objectives

  • At the end of the experiment, students should be able to:

    • Use standard laboratory instruments to measure mass, volume, and length.

    • Use measurements for calculating area and volume.

    • Determine the density of water and of shaped objects.

    • Calculate mean, standard deviation, and relative standard deviation.

    • Calculate percentage of error or bias.

Significant Figures

Definition

  • Numbers in science are either measured (with significance determined by the tool used) or exact (infinite significant figures).

  • Example Usage:

    • Ruler with lines at 1/16” intervals provides a specific level of measurement.

    • A balance may measure to the nearest 0.1 grams.

Rules for Handling Zeros

  1. Leading Zeros: Not significant (e.g., 0.421 has 3 significant figures).

  2. Captive Zeros: Significant (e.g., 4012 has 4 significant figures).

  3. Trailing Zeros: Significant if a decimal is present (e.g., 114.20 has 5 significant figures).

Calculating Values

Multiplication and Division

  • Result retains the same number of significant figures as the factor with the fewest significant figures.

    • Example: 0.24 kg x 4621 m = 1100 m (2 significant figures).

Addition and Subtraction

  • The number of significant figures aligns with the position of the first uncertain digit.

    • Example: 0.240 m + 0.30 m = 0.540 m (3 significant figures).

Observations in Science

Accuracy vs Precision

  • Accuracy: Closeness of a measurement to the true value.

  • Precision: Consistency of repeated measurements.

  • Example Scenarios:

    • Poor precision and accuracy: Darts scattered across the board.

    • Good precision but poor accuracy: Darts clustered together but away from the target.

    • Good precision and accuracy: Darts are clustered close to the target (bull's-eye).

Materials and Apparatus

  • Balances:

    • 1 Analytical Balance

    • 1 Top-loading Balance

  • Containers:

    • 1 Beaker (250 mL)

    • 3 Erlenmeyer Flasks (50 mL)

    • 1 Graduated Cylinder (50 mL)

  • Tools:

    • 1 Thermometer

    • 1 Caliper or Foot Rule

  • Chemicals:

    • Distilled water, marbles (option 1), coins (option 2).

Procedures

Part A: Use of Balance

  1. Obtain 100 mL of distilled water in a beaker.

  2. Use a thermometer to measure the temperature of water and laboratory.

  3. Measure and record the mass of the stoppered flask using the balance.

  4. Record combined mass repeatedly for consistency.

  5. Calculate the mean mass and consult instructor for discrepancies.

Part B: Calibration of Pipette

  1. Practice using a 5 mL pipette with distilled water.

  2. Measure the laboratory temperature and that of the water.

  3. Measure mass of the combined flask and 5 mL water.

  4. Record measurements for subsequent volumes (10, 15, 20 mL).

  5. Use temperature data to find the density of water from Table 1.

Part C: Density of an Object

  1. Measure 40-50 mL water in a graduated cylinder.

  2. Determine the mass of marbles/coins using the analytical balance.

  3. Submerge object to measure the displaced volume.

  • Calculate volume: Initial volume - displaced volume.

  1. Measure length, width, and height of the object with caliper.

  2. Use measurements to calculate volume and then density.

Calculations

  • Density Calculation:

    • Density = Mass/Volume

    • Significant figures applied to calculations.

Conclusion

  • Understanding measurements and statistical analysis is critical in analytical chemistry. Proper practices regarding significant figures, accuracy, and precision are essential for conducting reliable experiments.