Physical & Chemical Properties, Matter Classification, and Separation Techniques

Physical Properties – Definition & Illustrative Cases

• A physical property can be observed or measured without altering the substance’s chemical identity.

  • Classic examples: melting, boiling, freezing, condensing, sublimation, deposition.

  • Mechanical change (e.g., crushing a rock) alters shape/size but keeps identity intact.

• Additional physical‐property keywords found in the lecture:

  • Density, mass, volume, specific heat (heat capacity), thermal conductivity, electrical conductivity, malleability, ductility, solubility.

  • "Conducts electricity" is strictly physical: current flows through the existing material; no new species appear.

• Density relationship (all units must match):
  $\rho = \dfrac{m}{V}$
  where $m$ = mass, $V$ = volume, $\rho$ = density.

Key Units & Conversions Mentioned

• Mass: gram (g), milligram (mg).

• Volume: cubic centimetre (cm$^3$), millilitre (mL), and cc (medical shorthand). 1 mL = 1 cm$^3$ = 1 cc.

• Energy (heat): joule (J) or calorie (cal).
  • 1 cal ≈ 4.184 J (constant not stated explicitly but standard).

Heat Capacity & the $q = m c \Delta T$ Relationship

• Heat absorbed or released without chemical change is calculated by
  $q = m \, c \, \Delta T$
  where
  • $q$ = heat (J or cal)
  • $m$ = mass (g)
  • $c$ = specific heat (J g$^{-1}$ °C$^{-1}$)
  • $\Delta T = T<em>{\text{final}} - T</em>{\text{initial}}$ (°C).

• Mnemonic shared: “m-cat” ( $q = m c \Delta T$ ).

• Example numeric mention: “1.45 J of heat raises 1 g of a sample by 1 °C” – this value is that sample’s specific heat.

• Heat capacity is entirely a physical property because no bonds break/form while heat is absorbed.

Electrical Conductivity – Pure Water vs Ionic Solutions

• Pure water is a very poor conductor: roughly 1 in 1 000 000 molecules self-ionise.

• Conductivity arises when mobile ions are present (dissolved salts, acids, bases, perspiration, pool chlorine, etc.).

  • Any ion concentration → charged particles move → current flows → possibility of shock/burn if potential is high enough.

Mechanical Properties – Iron Example

• Iron’s malleability & ductility are described as “average for a metal”.

  • Malleable: can be hammered or rolled into sheets without breaking.

  • Ductile: can be pulled into wires; resists fracture under tensile stress.

• Still a physical discussion; iron remains elemental Fe throughout deformation.

Chemical Properties & Reactions

• Chemical property = ability of a substance to undergo a change that alters its chemical composition.

  • Synonym: chemical change = chemical reaction.

• Arrow notation: $\text{Reactant}<em>A + \text{Reactant}</em>B \;\rightarrow\; \text{Product}_C$
  • Left of arrow → reactants.
  • Right of arrow → products.

• Indicators/terms signalling chemical change: burning, cooking, rusting, oxidising, souring of milk, fruit ripening, color change produced (not mere dilution).

• Oxidation: broad class involving reaction with O₂; covers burning, rust, some color changes.

Acid–Base Fundamentals Introduced

• Arrhenius-style definitions employed in class:

  • Acid → produces $\text{H}^+$ in water.
    • Example: $\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$

  • Base → produces $\text{OH}^-$ in water.
    • Example: $\text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^-$

• “Caustic” and “corrosive” are descriptive labels often applied to strong acids/bases because of their reactivity with tissues/metals.

Atomic & Ionic Structure Refresher

• Atom ≈ small sphere consisting of:

  • Nucleus: protons (+), neutrons (0)

  • Electrons: negative, orbit nucleus.

• Atomic number (Z) = number of protons = number of electrons in a neutral atom.

• On periodic table:

  • Metals (left of stair-step line) tend to lose e⁻ → cations (+).
    • Group 1 metals (Li, Na, K…) usually form +1 ions (e.g., $\text{Na}^+$).

  • Non-metals (right) tend to gain e⁻ → anions (−).

• Chemical reactions involve electron exchange or sharing only—nuclear particles (p⁺, n⁰) stay put unless nuclear reactions occur.

Vocabulary: Stability & Reactivity

• Stability = lack of tendency to react under stated conditions.

• Reactivity = readiness to undergo chemical change.
  • Both are descriptors of chemical behaviour (not physical).

• Flammable / combustible / oxidising all imply reaction with O₂ and are chemical in nature.

Evaluating Sample Statements (Physical vs Chemical)

• “Molten salt conducts electricity” → physical (conductivity).

• “Silver nitrate added to NaCl solution forms a white solid” → chemical (precipitation of $\text{AgCl}$).

• “Electricity passed through molten salt yields a grey metal at one terminal and green-yellow gas at the other” → chemical (electrolysis producing Na(s) & Cl₂(g)).

Classification of Matter

• Pure Substance: constant composition everywhere, homogeneous at molecular level.
  • Sub-categories: elements (single type of atom) & compounds (fixed ratio of different atoms).
  • Cannot be separated by physical means; require chemical or nuclear processes.

• Mixture: physical blend of two+ pure substances; composition can vary.
  • Can be separated by physical processes.
  • Exhibit properties that depend on their particular ratios (% by mass, volume, molarity, etc.).

Mixtures – Homogeneous vs Heterogeneous

• Homogeneous mixture (solution): uniform phase throughout; e.g., NaCl(aq), air, brass.

• Heterogeneous mixture: visibly distinct parts or phases; e.g., ice cubes in Kool-Aid, sand in water, milk that has curdled.

• Example percentages supplied:

  • 20 g NaCl + 80 g H₂O → 20 % solution.

  • 40 g NaCl + 60 g H₂O → 40 % solution.
    Changing ratio = still the same mixture type, not a new compound.

Physical Methods for Separating Mixtures

(All leave chemical identities untouched)

• Filtration – exploits particle size/state (solid vs liquid).

• Evaporation – allows solvent to vaporise, leaving solute(s).

• Distillation – boils components, condenses lower-boiling component; apparatus: boiling flask → condenser → collection vessel.

• Chromatography – separates by differential adsorption & solubility along a stationary phase.

• Centrifugation – uses rotational acceleration; dense phases move outward, lighter stay near centre.

Energy Hierarchy Mentioned

• Physical change energy (e.g., phase change) < chemical change energy (bond formation/cleavage) < nuclear change energy (splitting atoms).

• Splitting an atom (nuclear fission) demands vastly greater energy than any chemical or physical process.

Quick Reference Equation List

• Density: $\rho = \dfrac{m}{V}$

• Heat (specific heat): $q = m c \Delta T$

• Example acid dissociation: $\text{HX} \rightarrow \text{H}^+ + \text{X}^-$

• Example base dissociation: $\text{MOH} \rightarrow \text{M}^+ + \text{OH}^-$

These bullet-point notes consolidate every major and minor point, definitions, formula, unit, exemplar, and conceptual link raised in the transcript. They are structured for rapid review before quizzes or exams on introductory chemistry concepts such as properties of matter, classification, and separation techniques.