Chapter 1: Science and Measurement

What is Chemistry?

Chemistry is the study of matter, its transformations, and its interactions, focusing on the connections between molecular and macroscopic events. It is central to scientific knowledge and helps explain phenomena such as why colored fabrics fade in sunlight.

• Matter: Anything that occupies space and has mass (e.g., water, earth, trees).

• Chemistry's Core: Understanding the properties and changes of matter through experiments guided by theory and past experience.

The Scientific Method

The scientific method is a systematic approach to investigating natural phenomena. It involves observation, hypothesis formation, experimentation, and theory development.

• Observation: Measurement or description of some aspect of nature (e.g., boiling point of water at different altitudes, conservation of mass).

• Hypothesis: A tentative explanation for a set of observations.

• Law: A statement that summarizes a large number of observations but does not provide an explanation (e.g., water boils at lower temperature at higher altitudes).

• Theory: An explanation of the laws of nature, tested by experiments and valid only if consistent with all results to date.

• Experiment: A test of a hypothesis or theory; results may lead to modification of the theory.

Additional info: The process of refining theories based on experimental evidence is fundamental to scientific progress.

Mathematical Tools in Chemistry

Equations and Algebraic Manipulation

Solving chemical problems often requires manipulating equations to isolate variables and solve for unknowns.

• Equations with Two Unknowns: Systems of equations can be solved using substitution or elimination methods.

• Isolating Variables: Rearranging equations (e.g., ) to solve for a specific variable.

• Distributive Property:

• Order of Operations: Parentheses, exponents, multiplication/division, addition/subtraction (PEMDAS).

• Quadratic Equation: Solution:

Percentage Calculations

Percentages are used to express proportions, such as concentration of solutions.

• Percentage Formula:

Classifications of Matter

Types of Matter

Matter can be classified based on its composition and properties.

• Pure Substance: Has a definite (constant) composition and distinct properties. Examples: water, gold, ammonia.

• Element: A substance that cannot be separated into simpler substances by chemical means (e.g., Cu, Au, Ag).

• Compound: A substance composed of atoms of two or more elements chemically united in fixed proportions (e.g., table salt, water).

• Mixture: A combination of two or more substances in which the substances retain their distinct identities. Mixtures can be separated by physical means.

Types of Mixtures

• Homogeneous Mixture (Solution): Composition is uniform throughout (e.g., dissolved sugar in water, air).

• Heterogeneous Mixture: Composition is not uniform; different parts have different compositions (e.g., sand in water, salad).

Examples:

• The air we breathe is a mixture of several gases (e.g., O2, H2, N2).

• Sea water is a mixture of water (H2O) and salt (NaCl).

States and Properties of Matter

States of Matter

• Solid: Molecules are held close together in an orderly fashion with little motion.

• Liquid: Molecules are close together but not held rigidly; they can move past one another.

• Gas: Molecules are separated by large distances and move freely.

Physical and Chemical Properties

• Physical Property: Can be measured or observed without changing the composition or identity of a substance (e.g., melting point, density).

• Chemical Property: Requires a chemical change to observe (e.g., flammability, reactivity with acid).

Extensive Property: Depends on the amount of matter (e.g., mass, volume). Intensive Property: Does not depend on the amount of matter (e.g., density, temperature).

Measurement and Units

SI Units

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

Unit Conversions

• 1 km = 1000 m

• 1 m = 100 cm

• 1 cm = 10 mm

• 1 kg = 1000 g

• 1 lb = 453.59 g

• 1 L = 1000 mL = 1 dm3

Example: To convert 45 inches to kilometers, use the appropriate conversion factors.

Density

Density is the ratio of mass to volume.

• Formula:

• Common units: g/mL, kg/m3

Example: Show how 1 g/cm3 is equal to 1000 kg/m3.

Temperature Scales

• Conversion Formulas:

Note: Temperatures in Kelvin can never be negative.

Scientific Notation

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

• Example:

• Speed of Light: mi/s

Operations with Scientific Notation

• Addition/Subtraction: Combine quantities with the same exponent.

• Multiplication: Multiply the decimal parts and add the exponents.

• Division: Divide the decimal parts and subtract the exponents.

Significant Figures

Rules for Significant Figures (SF)

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros in a number with a decimal point are significant.

• Trailing zeros in a whole number without a decimal point are ambiguous.

Examples:

• 0.478 cm (3 SF), 102.4 lb (4 SF), 0.023 g (2 SF), 1.0023 min (5 SF)

Significant Figures in Calculations

• Addition/Subtraction: The answer should have no more digits to the right of the decimal point than the original number with the fewest such digits.

• Multiplication/Division: The answer should have the same number of significant figures as the original number with the fewest significant figures.

Rounding Rules:

• If the digit to be dropped is less than 5, drop it.

• If the digit is 5 or greater, increase the preceding digit by 1.

Accuracy and Precision

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

• Precision: How closely repeated measurements agree with each other.

Example: Measuring the boiling point of water three times and getting similar results demonstrates precision; getting the correct value demonstrates accuracy.

Sample Problems and Applications

• Convert mass from kilograms to pounds using conversion factors.

• Convert density from kg/m3 to g/cm3 and lb/cm3.

• Convert large quantities (e.g., billion pounds to tons).

• Calculate the density of a metal using mass and volume measurements.

• Calculate the diameter of a cylindrical tube given mass, density, and length.

• Determine the area of gold leaf produced from a given mass of gold and its density.