Chemistry Basics Quiz

Chemistry: The Central Science - Chapter 1

• Chemistry is the study of matter, its properties, and the changes it undergoes.
• Chemistry underpins the fundamental understanding of many science-related fields.
• Matter is anything that has mass and takes up space.

Classifications of Matter

• Matter exists in three states: solid, liquid, and gas.
• Matter can be classified by its composition: elements or compounds.
  • Elements consist of only one type of atom.
  • Compounds contain two or more different types of atoms bonded together.
• Mixtures can vary in composition throughout a sample (heterogeneous) or have the same composition throughout the sample (homogeneous).
• A homogeneous mixture is also called a solution.

Representing Elements

• Chemists use symbols to represent elements.
• Symbols are typically one or two letters; the first is always capitalized.
• Some element symbols are derived from Latin or Greek names.

Elements and Composition

• There are currently 118 named elements.
• The five primary elements that comprise 90% of the Earth's crust by mass are: Aluminum, Iron, Calcium, Silicon, and Oxygen.
• Three elements make up 90% of the human body by mass; Oxygen, Carbon, and Hydrogen.
• Oxygen plays a crucial role in both the Earth's crust and the human body.

Compounds and Composition

• Compounds have a definite composition.
• The relative number of atoms of each element in a compound remains consistent in any sample (Law of Constant Composition).

Mixtures

• Mixtures exhibit the properties of their constituent substances.
• Mixtures can have varying compositions (heterogeneous) or uniform composition throughout the sample (homogeneous).
• Homogenous mixtures are also called solutions.
• Mixtures can be separated based on physical properties—methods like filtration, distillation, and chromatography.

Making a Decision (Classifying Matter)

• The flowchart on page 11 outlines a structured method for classifying matter as homogenous mixtures, heterogeneous mixtures, elements, or compounds.

Properties of Matter

• Properties are characteristics of a substance.
• Physical properties can be observed without changing the substance's identity (e.g., color, odor, density, melting point, boiling point, and hardness).
• Chemical properties describe how a substance reacts to form a new substance (e.g., flammability, ability to rust, oxidation).
• Intensive properties are independent of the amount of substance (e.g., density, boiling point).
• Extensive properties depend on the amount of substance (e.g., mass, volume).

Physical and Chemical Changes

• Physical changes alter a substance's physical properties but do not change its composition (e.g., changes of state, temperature, or volume).
• Chemical changes produce new substances with different properties (e.g., combustion, oxidation, and decomposition).

Separating Mixtures

• Mixtures can be separated using techniques based on physical properties of the components.
• Examples include filtration, distillation, and chromatography.

Energy

• Energy is the capacity to do work or transfer heat.
• Work is energy transferred when a force causes an object's displacement.
• Heat is the energy used to change an object's temperature.
• Force is a push or pull on an object.

Two Fundamental Forms of Energy

• Kinetic energy is the energy of motion and depends on an object's mass and velocity.
• Potential energy is stored energy based on an object's position relative to other objects.

Units of Measurement

• Numbers are critical in chemistry, with many topics being quantitative.
• Units of measurement are essential in science.
• Quantities are measured and calculated using units.
• Uncertainty exists in measurements. Significant figures indicate the precision of a measurement and are used in calculations.
• Dimensional analysis converts values from one unit to another using conversion factors.

Units of Measurement-SI Units

• SI units are a standard system of measurement.
• Different base units exist for each measurable quantity.

Units of Measurement-Metric System

• The metric system uses base metric units for quantities like mass, length, time, temperature, amount of substance, volume.
• Prefixes are used to adjust base units to convenient sizes for common usage (e.g., liters).

Significant Figures

• All digits in a measured value are significant, including the uncertain ones.
• Significant figures are essential to avoid overstating the accuracy of answers in calculations.
• When performing calculations, follow rules regarding significant figures in addition/subtraction and multiplication/division.
• Measurement has uncertainty. The last reported digit is reliable, but not perfectly accurate.

Significant Figures Rules

• Non-zero digits are significant.
• Zeros between non-zero digits are significant.
• Leading zeros are not significant.
• Trailing zeros are significant if a decimal point is present.

Significant Figures in Calculations

• The least precise measurement affects the precision of the answer.
• Results from addition/subtraction to the decimal place of the least precise measurement.
• Results from multiplication/division with the same number of significant figures as the least precise measurement.

Dimensional Analysis

• Dimensional analysis uses conversion factors based on equalities to change units in calculations.
• These factors are set up as ratios, allowing units to cancel out leaving the desired unit.
• Multiple conversions are possible, but each conversion must be an equality.

Density

• Density is the mass per unit volume of a substance (mass ÷ volume).
• Common units include grams per milliliter (g/mL) and grams per cubic centimeter (g/cm³).

Energy Units

• The Joule (J) is the SI unit of energy that describes the power of a substance (rate of energy consumption or production).
• Other energy units exist and were historically used (e.g., Calories).

Uncertainty in Measurements

• Measuring devices have varying degrees of accuracy.
• Measured numbers always have uncertainty.
• The last reported digit is an estimate, and not exact.

Numbers Encountered in Science

• Exact numbers arise from counting or definitions.
• Inexact (measured) numbers have inherent uncertainty due to limitations of instruments & measuring techniques (e.g., human error).
• Uncertainties exist in measured numbers.

Precision Versus Accuracy

• Precision is how closely measurements agree with each other.
• Accuracy is how closely measurements agree with the true value.
• Standard deviation is often used in experiments to assess accuracy and precision