Chemistry - Scientific Method & Measure

Scientific Method

• Definition: The scientific method is an orderly and systematic approach to solving problems. It can be applied to both scientific inquiries and everyday challenges.

Steps of the Scientific Method

• Observation: Initial stage where something is noted and calls for inquiry.

• Develop a Question: Formulating what you want to know based on the observation.

• Form a Hypothesis: Creating an educated guess or prediction to answer the question.

• Perform an Experiment and Analyze Data: Testing the hypothesis through controlled experimentation and evaluating the results.

• Draw a Conclusion: Summarizing the findings and determining if the original hypothesis was supported or refuted.

Everyday Example of Scientific Method

• Scenario: Sara notices she needs a date for Friday night.

  • Observation: Sara is at the observation stage of the scientific method.

• Question Development: She asks herself, "Could Ben be my date?"

  • Current Step: Developing the question.

• Hypothesis: Sara hypothesizes that Ben will indeed go out with her.

  • Definition: A hypothesis is an educated guess that can be tested.

• Experiment: To test the hypothesis, Sara asks Ben out, saying:

• Result: Ben responds:

• Analysis: Analyzing the data (Ben's response), Sara concludes her hypothesis was incorrect—it was determined that Ben would not be her date.

• New Hypothesis: Sara does not give up and contemplates, "Maybe Josh will be my date."

Variables in Scientific Experiments

• Definition of Variable: A variable is a factor being tested in an experiment.

• Types of Variables:

  • Independent Variable: The factor manipulated by the investigator; it is the specific treatment or condition of interest.

  • Dependent Variable: What is measured or observed; this represents the collected data resulting from changes in the independent variable.

  • Experimental Group: Participants exposed to the independent variable.

  • Control Group: Participants treated identically to the experimental group but not exposed to the independent variable; serves as a baseline for comparison.

Scientific Laws vs. Theories

• Natural Laws: Descriptions of observed phenomena—express how nature behaves without explaining why. Typically recognized as true and can sometimes be expressed mathematically.

  • Example: Newton’s Laws of Motion.

• Theory: An explanation of why nature behaves as described by a natural law.

  • Characteristics of Theory:

  • More robust than a hypothesis

  • Explains a set of related observations based on proven hypotheses, verified multiple times through rigorous testing by different researchers.

  • Notable Example: Einstein’s Theory of Relativity.

Application of the Scientific Method

• Example Situation: A study on the drug lovastatin, suspected to reduce spasticity in patients with AMN (a neurological disease).

  • Study Design:

  • 50 patients administered lovastatin

  • 50 patients given a placebo.

• Key Questions:

  • What is the hypothesis?

  • Identify the independent variable.

  • Identify the dependent variable.

  • Which group is the control group?

Scientific Notation, Metric Conversions, and Dimensional Analysis

Scientific Notation

• Steps for Conversion:

  1. Move the decimal point after the first digit and drop the trailing zeros.

  • Example: 123,000,000,000 → 1.23

  1. Count the places moved to determine the exponent; this is added to the base 10.

  • Example: In 123,000,000,000, the decimal moves 11 places, so it is written as $1.23 imes 10^{11}$.

  1. Numbers less than 1 will have negative exponents.

  • Example: $0.000001$ is written as $1 imes 10^{-6}$.

• Practice Conversions:

  • Convert the following:

  • $0.005$

  • $5,050$

  • $0.0008$

  • $1,000$

  • $1,000,000$

  • $0.25$

  • $0.025$

  • $0.0025$

  • $500$

  • $5,000$

International System of Units (SI)

• Base Units: The foundation for all metric measurements, categorized into seven base units:

  • Length: meter (m)

  • Mass: kilogram (kg)

  • Time: second (s)

  • Temperature: Kelvin (K)

  • Amount of Substance: mole (mol)

  • Electric Current: ampere (A)

  • Luminous Intensity: candela (cd)

• Prefixes: Used with SI base units to represent larger or smaller quantities:

  • Metric Prefixes and Symbols:

  • Kilo – k

  • Hecto – h

  • Deka – da

  • BASE

  • Deci – d

  • Centi – c

  • Milli – m

  • Mnemonic: "King Henry Died By Drinking Chocolate Milk" helps to remember order of prefixes.

Metric Conversions and Practice Problems

• Practice Conversions:

  • Convert the following:

  • $100m = ext{?} km$

  • $3m = ext{?} mm$

  • $230cm = ext{?} m$

  • $461mm = ext{?} m$

  • $2500m = ext{?} km$

  • $4500mg = ext{?} g$

  • $2000g = ext{?} mg$

  • $200g = ext{?} kg$

  • $23L = ext{?} mL$

  • $0.14mm = ext{?} m$

  • $1550mm = ext{?} m$

  • $4000mL = ext{?} L$

  • $1.4kg = ext{?} g$

  • $1452mg = ext{?} g$

  • $9.5m = ext{?} cm$

Derived SI Units

• Key Derived Units:

  • Area: square meter (m²)

  • Volume: cubic meter (m³)

  • Density: kilograms per cubic meter (kg/m³)

  • Molar Mass: kilograms per mole (kg/mol)

  • Concentration: moles per liter (M)

  • Molar Volume: cubic meters per mole (m³/mol)

Dimensional Analysis

• Definition: Technique for converting between units.

• Uses:

  1. Unit Equalities: Equations that relate different units (e.g., $1 cm = 0.01 m$).

  2. Conversion Factors: Equations that equal one (e.g., $rac{1 cm}{0.01 m}$).

  • Process: Multiply by the conversion factors so that unwanted units cancel out and the desired unit remains.

• Unit Equalities for Dimensional Analysis:

  • $2.54 cm = 1 in$

  • $12 in = 1 ft$

  • $3 ft = 1 yd$

  • $5280 ft = 1 mi$

  • $1.6 km = 1 mi$

  • $4.184 J = 1 cal$

  • $1000 J = 1 kJ$

  • $1 km = 1000 m$

  • $1 dm = 100 mm$

• Practice Problems:

  • $64.5 dm = ext{? mm}$

  • $91.2 m = ext{? km}$

  • $96.5 in = ext{? yds}$

  • $1.235 ft = ext{? cm}$

  • $8.95 kJ = ext{? cal}$

  • $34.5 miles = ext{? m}$

  • $52.3 cm = ext{? ft}$

  • $6.98 m/min = ext{? km/hr}$

  • $59.63 cal = ext{? J}$

  • $96.5 kJ = ext{? cal}$

  • $1 year = ext{? sec}$