Exploring Chemical Properties and Changes

Chemical Properties

• Chemical properties describe how a substance interacts with others, forming new substances during a chemical reaction.
• Examples include reactivity with water, acids, and oxygen.
• Combustibility is a chemical property defined as a substance's ability to burn in the air.
• Stability, another chemical property, indicates a substance's ability to remain unchanged.
• Toxicity, or the ability of a substance to cause harm, is also a chemical property.
• Toxicity is quantified as the LD50 value, and can be acute (severe and sudden) or chronic (long-term).
• Stability and toxicity are often linked.

Chemical vs. Physical Changes

• Physical changes do not alter the composition of a substance; they affect state or volume.
• Chemical changes result in the formation of new substances through processes like oxidation or decomposition.

Matter and Its Properties

• Everything is either matter or energy
• Matter has mass and occupies space
• Matter is composed of tiny particles that attract each other and are always in motion.
• Particle motion increases with temperature.
• Atoms serve as the building blocks of matter.
• An element consists of identical atoms.
• A compound is composed of two or more elements.
• The three states of matter are solid, liquid, and gas.

Classification of Matter

• Matter can be classified as either a mixture or a pure substance.
• Uniformity determines whether matter is categorized as homogenous or heterogeneous.
• Homogenous matter with variable composition is a mixture or solution.
• Homogenous matter with fixed composition is a pure substance.
• Pure substances are either elements (cannot be broken down) or compounds (can be broken down).
• Heterogeneous mixtures are also known as mechanical mixtures, while homogeneous mixtures are uniform.

Elements vs. Compounds

• An element is a pure substance that cannot be broken down by chemical or physical means (e.g., helium, oxygen).
• A compound is a pure substance that can be broken down by chemical methods (e.g., water H2O).
• Compounds consist of two or more elements chemically combined.

Mixtures

• Mixtures contain more than one kind of particle.
• Examples include water, salt, air, and vinegar.
• Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).
• Mixtures can be separated through physical methods.

Separation Techniques

• Filtration separates solids from liquids and solutions.
• Distillation separates homogeneous mixtures based on boiling points.

Physical Properties

• Physical properties can be observed and measured without changing a substance's identity.
• Physical properties are either intensive or extensive.
• Intensive properties are independent of the amount of substance present.
• Extensive properties depend on the amount of substance present.

Qualitative vs. Quantitative Physical Properties

• Qualitative properties are described using the five senses (e.g., state, luster, malleability, color, odor).
• Quantitative properties are measured and assigned a value (e.g., melting/boiling point, solubility, hardness, conductivity, density, viscosity).
• Diamond is the hardest known material.

States of Matter

• States of matter are physical properties.
• Boiling and melting points relate to changes of state.
• Freezing: liquid to solid
• Melting: solid to liquid
• Evaporation: liquid to gas
• Condensation: gas to liquid
• Sublimation: solid to gas
• Deposition: gas to solid

Quantitative Properties

• Solubility is the maximum amount of solute that can dissolve in a solvent at a given temperature.
• Solubility is expressed as the mass of solute per mass of solvent or vice versa.
• Solutions with water as the solvent are aqueous solutions.
• Fat solubility can lead to bioaccumulation and biomagnification of toxins like DDT in the food chain.
• Hardness is the ability to scratch a material, measured by the Mohs scale.

Density

• Density is the ratio of mass to volume.
• Water is the universal solvent and is denser as a liquid than as a solid.
• Water is the only natural substance that exists as solid, liquid, and gas on Earth.

Density Calculations

• Mass is measured using triple-beam, electronic, and spring balance scales.
• Density is measured in g/mL (liquids) or g/cm3 (solids).
• Volume of symmetrical objects can be measured with a ruler.
• Volume of asymmetrical objects is determined by water displacement (Vf - Vi).

GRASP Method

• G = Given: List the provided information.
• R = Required: State what needs to be solved.
• A = Analysis: Identify the relevant equation.
• S = Solution: Show step-by-step problem-solving with units.
• P = Paraphrase: State the final answer.

Units for GRASP

• Density: g/cm3 (solids) or g/mL (liquids)
• Mass: grams (solids) or mL (liquids)
• Volume: mL or cm3