Scientific Inquiry and the Scientific Method

Observation and Inference

Scientific inquiry begins with careful observation and the distinction between observation and inference. These are foundational to forming hypotheses and conducting experiments.

• Observation: Information gathered by the five senses. Can be qualitative (descriptive, without numbers) or quantitative (involving numbers, counts, or measurements).

• Inference: An assumption or interpretation based on observations and prior knowledge.

• Example: Observing that a book is 455 mm tall (quantitative observation); inferring that the book is heavy (inference).

Research and Hypothesis

Research involves proposing explanations for observed phenomena. Hypotheses must be testable and serve as starting points for further investigation.

• Hypothesis: A prediction or explanation of a phenomenon. Must be testable and falsifiable.

• Theory: An explanation for a phenomenon that has been widely supported by evidence and experimentation.

• Law: A description (often mathematical) of a phenomenon. Does not explain why the phenomenon occurs.

• Example: "If plants are given more sunlight, then they will grow taller." (Hypothesis)

Experimentation

Experiments are designed to test hypotheses by manipulating variables and observing outcomes.

• Control Group: The group not experimented upon, used as a reference for comparison.

• Experimental Group: The group that receives the experimental treatment.

• Independent Variable: The variable that is changed or manipulated.

• Dependent Variable: The variable that is measured; it depends on the independent variable.

• Example: Testing the effect of room temperature on sleep hours. Independent variable: temperature; dependent variable: hours of sleep.

Conclusion and Reporting

After experimentation, conclusions are drawn and results are reported, often leading to further questions and investigations.

Textbook Scientific Method

The traditional scientific method is often presented as a linear sequence of steps, but in practice, scientific inquiry is more flexible and iterative.

• Not all steps must be completed in strict order.

• Scientists may revisit earlier steps as new data emerges.

Measurement in Chemistry

Uncertainty and Significant Figures

All measurements have some degree of uncertainty, which is reflected in the use of significant figures.

• Uncertainty: The plus or minus value indicating the range within which the true value lies.

• Significant Figures (Sig Figs): Digits in a measurement that are known with certainty plus one estimated digit.

• Rules for Significant Figures:

  • All nonzero digits are significant.

  • Zeros between nonzero digits are always significant.

  • Leading zeros are never significant.

  • Trailing zeros are significant only if a decimal point is present.

• Example: 1.37 ± 0.05 cm (the uncertainty is ±0.05 cm)

Significant Figures in Calculations

• Addition/Subtraction: The answer is rounded to the same decimal place as the least certain measurement.

• Multiplication/Division: The answer is rounded to the same number of significant figures as the measurement with the fewest significant figures.

• Example: (rounded to the tenths place)

• Example: (rounded to 2 significant figures)

Accuracy, Precision, and Error

Understanding the quality of measurements is essential in chemistry.

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

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

• Percent Error:

• Standard Deviation:

• Types of Error:

  • Random Error: Unavoidable fluctuations; affects precision.

  • Systematic Error: Consistent bias due to faulty equipment or technique; affects accuracy.

Units, Prefixes, and Scientific Notation

SI (Metric) Units

The International System of Units (SI) is the standard for scientific measurements.

• Base Units:

  Quantity	Unit	Symbol
  Mass	Kilogram	kg
  Length	Meter	m
  Time	Second	s
  Electric Current	Ampere	A
  Temperature	Kelvin	K
  Luminosity	Candela	cd
  Amount of Substance	Mole	mol

• Volume: Measured in liters (L), not a base SI unit.

SI Prefixes

Prefixes are added to base units to indicate multiples or fractions of units.

Scientific Notation

Scientific notation is used to express very large or very small numbers in the form , where and is an integer.

• Example: meters meters

Dimensional Analysis and Unit Conversions

Conversion Factors

Conversion factors are ratios used to express the same quantity in different units.

• Example: , so

Examples of Unit Conversions

• How many inches are in 128.5 feet?

• How many hours in 26.5 years?

Dimensional analysis uses unit cancellation to ensure correct conversions.

Summary Table: Types of Error

Additional info:

• Some context and examples were expanded for clarity and completeness.

• Tables and formulas were reconstructed for academic accuracy.