Chapter 3: Matter and Mixtures - Study Notes

Matter

  • Anything occupying space and having mass
  • Matter exists in three states: Solid, Liquid, Gas

The Three States of Water

  • Solid
    • Rigid
    • Has a fixed volume and shape
    • Examples: ice cube, diamond, iron bar
  • Liquid
    • Has a definite volume
    • Assumes shape of container
    • Examples: gasoline, water, alcohol, blood
  • Gas
    • Has no fixed volume or shape
    • Takes the shape and volume of its container
    • Examples: air, helium, oxygen
  • Water in all three phases: in all three phases, water molecules are still intact, but the motions of molecules and the distances between them change

Section 3.2: Physical and Chemical Properties and Changes

  • Physical Properties

    • Characteristics that are directly observable and unique to a substance
    • Examples: odor, color, volume, state, density, melting point, boiling point

  • Chemical Properties

    • A substance’s ability to form new substances
    • The characteristics that determine how the composition of matter changes as a result of contact with other matter or the influence of energy
    • Characteristics that describe the behavior of matter
    • Examples: flammability, rusting of steel, digestion of food

  • Concept Check 1: Classify each of the following as a physical or chemical property

    • Ethyl alcohol boiling at 78∘^\circC: physical
    • Hardness of a diamond: physical
    • Sugar fermenting to form ethyl alcohol: chemical

  • Physical Change

    • Change in one or more physical properties of a substance, and not in its chemical composition
    • Example: Boiling or freezing water

  • Three States of Water (revisited)

    • In all three phases, water molecules are intact, but molecular motions and intermolecular distances change

  • Chemical Change

    • A given substance becomes a new substance or substances with different properties and different composition
    • Example: Bunsen burner reaction where methane reacts with oxygen to form carbon dioxide and water
    • Chemical equation for electrolysis of water (illustrated later):
    • Water decomposes to hydrogen and oxygen gases
    • Overall: 2 H<em>2O(l)→2 H</em>2(g)+O2(g)2\,H<em>2O(l) \rightarrow 2\,H</em>2(g) + O_2(g)

  • Electrolysis of Water (continued)

    • Water decomposes to hydrogen and oxygen gases

  • Concept Check 2: Which of the following are examples of a chemical change?

    • a) Pulverizing or crushing rock salt: physical
    • b) Burning of wood: chemical
    • c) Dissolving of sugar in water: physical
    • d) Melting a popsicle on a warm summer day: physical

  • Concept Check 3: Classify each of the following as a physical or chemical change

    • Sugar fermenting to form ethyl alcohol: chemical
    • Iron metal melting: physical
    • Iron combining with oxygen to form rust: chemical

  • Electrolysis of Water (summary)

    • Water can be split into its elemental gases, hydrogen and oxygen, via electrolysis

Section 3.3: Elements and Compounds

  • Element
    • A substance that cannot be broken down into other substances by chemical methods
    • Examples: Iron, Fe; aluminum, Al; oxygen, O$2$; hydrogen, H$2$
    • All of the matter in the world around us contains elements
  • Compound
    • A substance composed of a given combination of elements that can be broken down into those elements by chemical methods
    • Examples: Water, H$2$O; carbon dioxide, CO$2$; table sugar, C${12}$H${22}$O$_{11}$
    • A compound always contains atoms of different elements
    • A compound always has the same composition or the same combination of atoms
  • Concept Check 4: How many of the following are compounds? H$2$O, N$2$O$4$, NaOH, MnO$2$, HF
    • Five – All of the substances are compounds

Section 3.4: Mixtures and Pure Substances

  • Pure Substances
    • Always have the same composition
    • Are either elements or compounds
    • Examples: pure water or H$2$O, carbon dioxide or CO$2$, hydrogen or H$_2$, gold or Au
  • Mixtures
    • Have variable composition
    • Examples: wood, wine, coffee
    • Can be separated into pure substances that are elements and/or compounds
  • Homogeneous Mixture (Solutions)
    • A substance that is the same throughout
    • Consists of visibly indistinguishable parts
    • Also called a solution
    • Does not vary in composition from one region to another
  • Homogeneous Mixture – Examples
    • Air around you
    • Brass
    • Table salt stirred into water
  • Heterogeneous Mixture
    • Consists of visibly distinguishable parts
    • Contains regions that have different properties from those of other regions
  • Heterogeneous Mixture – Examples
    • Oil and vinegar dressing
    • Sand stirred into water
  • Concept Check 5: Which of the following is a homogeneous mixture?
    • Pure water: yes (homogeneous)
    • Gasoline: yes (homogeneous)
    • Jar of jelly beans: no (heterogeneous)
    • Soil: no (heterogeneous)
    • Copper metal: no (element)

Section 3.5: Separation of Mixtures

  • Separation Based on Physical Properties
    • Mixtures can be separated based on different physical properties of the components
    • Techniques and corresponding properties:
    • Boiling point — Distillation
    • State of matter (solid/liquid/gas) — Filtration
    • Adherence to a surface — Chromatography
    • Volatility — Evaporation
  • Distillation of a Solution Containing Salt in Water
    • Distillation of Salt Water
    • No chemical change occurs when salt water is distilled
  • Filtration
    • Separates a liquid from a solid

The Organization of Matter

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