Acids Naming Rules and Examples (Transcript Notes)

Acid naming rules and examples from the transcript

  • Core idea: The formula starts with H; H⁺ is the cation in the net compound, and the compound’s name is determined from the anion. Substances that donate H⁺ in water are acids.

    • The speaker emphasizes naming the acid from the anion’s name.
    • Important correction (instructor confusion in transcript): HCl is hydrochloric acid, not hydrofluoric acid. Hydrofluoric acid corresponds to HF.

  • What matters is the ion by itself (the anion) when naming the acid.

    • Fluoride ion: fluoride (ends with -ide).
    • Chloride ion: chloride (ends with -ide).

  • Binary acids vs. oxyacids (implicit in the discussion of naming):

    • When the anion ends in -ide and is a simple nonmetal, the acid name uses the hydro- prefix and the -ic acid ending (e.g., HCl as hydrochloric acid; HF as hydrofluoric acid).
    • When the anion is polyatomic and ends in -ate or -ite, the acid name is derived from the root of the anion with -ic or -ous acid endings respectively (e.g., nitrate → nitric acid; nitrite → nitrous acid).

  • The “shortest, easiest rule” highlighted for polyatomic ions:

    • Nitrate (NO₃⁻) forms nitric acid (HNO₃).
    • Nitrite (NO₂⁻) forms nitrous acid (HNO₂).
    • Nitrite would typically be accompanied by one H⁺ to balance the negative charge, giving HNO₂.
    • The rule is that -ate → -ic acid, -ite → -ous acid.

  • Specific examples and their acids (as given or implied in the transcript):

    • Nitrate ion NO₃⁻ → Nitric acid HNO₃.
    • Nitrite ion NO₂⁻ → Nitrous acid HNO₂.
    • Sulfate ion SO₄²⁻ → Sulfuric acid H₂SO₄ (note the correct form; the transcript says it but emphasizes the correct name).
    • Cyanide ion CN⁻ → Hydrocyanic acid HCN (the acid form uses a -ide base and the hydro prefix).
    • Cyanide safety: cyanide is poisonous; hydrocyanic acid is also dangerous and is a gas.
    • Bromite ion BrO₂⁻ → Bromous acid HBrO₂ (the transcript says “bromite acid”; correct acid name is bromous acid).

  • General naming conventions reflected in the transcript:

    • For ions ending in -ide: the acid name uses the prefix hydro- and -ic acid (e.g., Cl⁻ → HCl, HF → HF). The example confusion in the transcript (HCl labeled as hydrofluoric acid) is corrected here.
    • For ions ending in -ate: the acid name ends with -ic acid (e.g., NO₃⁻ → HNO₃, nitrate → nitric acid).
    • For ions ending in -ite: the acid name ends with -ous acid (e.g., NO₂⁻ → HNO₂, nitrite → nitrous acid).

  • Additional context from the transcript (asides and digressions):

    • The speaker interjects about casual topics (e.g., weekend plans, dancing, personal plans) which are off-topic to the chemistry content. These can be ignored for study purposes but are part of the transcription record.

  • Safety and practical notes mentioned:

    • Hydrocyanic acid (HCN) is a gas and highly dangerous; cyanide compounds are poisonous.
    • Bromous acid (HBrO₂) is another example of an oxyacid derived from bromite BrO₂⁻.

  • Quick reference mappings (in LaTeX for formulas):

    NO_3^- + H^+

    ightarrow HNO_3

    NO_2^- + H^+

    ightarrow HNO_2

    SO_4^{2-} + 2H^+

    ightarrow H2SO4

    CN^- + H^+

    ightarrow HCN

    BrO_2^- + H^+

    ightarrow HBrO_2

    Cl^- + H^+

    ightarrow HCl

    F^- + H^+
    ightarrow HF

  • Connections to foundational principles:

    • Acids are substances that increase H⁺ concentration in water, lowering pH; acid naming aligns with the conjugate base (anion) formed when the acid dissociates in water.
    • The ability to predict the acid name from the anion improves chemical communication and stoichiometric calculations in reactions involving acids.

  • Notes on accuracy and sources:

    • The transcript contains a factual error in naming HCl as hydrofluoric acid; the corrected form is hydrochloric acid. HF is hydrofluoric acid.