Nomenclature of Acids and Hydrocarbons

Context & Motivation

Chemists frequently work with acids because many reactions proceed faster in acidic (aqueous) media.
Hydrocarbons appear in the lab as fuels (e.g.
Bunsen-burner gas); understanding their names helps classify and handle them.
The lesson’s mascot ("Professor Manatee") is a lighthearted anecdote—no technical content, but it reminds us the unit is meant to be short and approachable.

Acid Nomenclature

Acids are substances that, when dissolved in water, release $H^+$ ; bases release $OH^-$ .
The $H^+$ and $OH^-$ ions only exist in aqueous (water) environments; in the gas phase those ions are not present.
Naming depends on two decisions:
1. Is the substance dissolved in water (aq) or not?
2. Is the anion a binary ion (single element) or a polyatomic ion containing oxygen?

1. Gas vs. Aqueous

Example: $HCl(g)$ → “hydrogen chloride” (uses normal ionic/covalent rules).
$HCl(aq)$ → “hydrochloric acid.”
Always look for the (aq) tag (or are told "acid" on the test).

2. Two Naming Families

a. Ternary / Oxoacids (H⁺ + polyatomic anion with O)

Format: (root of anion) + ic acid.
Steps:
1. Identify the polyatomic anion that contains oxygen.
2. Replace the anion’s -ate ending with -ic.
3. Append “acid.”
Charge balancing: number of $H^+$ equals the anion’s negative charge; this does not affect the name.
Examples
- $H2CO3$ (carbonate $CO_3^{2-}$ ) → carbonic acid.
- $HClO3$ (chlorate $ClO3^-$ ) → chloric acid.
- $H3PO4$ (phosphate $PO_4^{3-}$ ) → phosphoric acid.
Exception: if the polyatomic anion lacks oxygen, treat it as binary (see cyanide below).

b. Binary Acids (H⁺ + single-element anion)

Format: hydro + (root of element) + ic acid.
Applicable whenever the negative ion is a single element (or a polyatomic without O).
Examples (all aqueous):
- $HBr$ → hydrobromic acid.
- $HF$ → hydrofluoric acid.
- $HI$ → hydroiodic acid.
- $H_2Se$ → hydroselenic acid (pronounced “sel-EN-ic”).
- $HCN$ (anion = cyanide, no O) → hydrocyanic acid.
Fun aside: $H_2O$ could be called “hydroxodic acid,” but chemists simply say water.

Quick Practice Summary (from video)

Formula	Analysis	Correct Name
$HF$	Binary; F⁻	hydrofluoric acid
$HI$	Binary; I⁻	hydroiodic acid
$H_2Se$	Binary; Se²⁻	hydroselenic acid
$H_2O$	Binary; O²⁻ (trivia)	water (not used)
$H<em>3PO</em>4$	Ternary; phosphate	phosphoric acid

Hydrocarbon (Alkane) Nomenclature

Hydrocarbon = molecules composed solely of carbon and hydrogen.
Focus family: alkanes (all C–C single bonds, “saturated” hydrocarbons).
Generic molecular formula: $CnH{2n+2}$ .
All names end in -ane.

Carbon-Count Prefixes (straight chains)

1 = meth 2 = eth 3 = prop 4 = but 5 = pent 6 = hex 7 = hept 8 = oct 9 = non 10 = dec
11 = undec 12 = dodec 13 = tridec 20 = icos 30 = tricos 40 = tetrac 100 = kilo

Naming Steps (Straight-Chain Alkane)

Count the number of carbon atoms $n$ .
Choose the corresponding prefix.
Add the family ending “-ane.”
(Optionally) write formula using $CnH{2n+2}$ to verify hydrogen count.

Examples

$C3H8$ → 3 C → propane.
$C7H{16}$ → 7 C → heptane.
$C9H{20}$ (displayed as $CH3(CH2)7CH3$ ) → 9 C → nonane.
Structural shorthand: a line-angle (“bond-line”) drawing of four connected vertices denotes butane (4 C’s).

Acceptable Structural Representations (any are credit-worthy)

Molecular formula: $C{11}H{24}$ (for undecane).
Condensed (parenthetical) formula: $CH3(CH2)9CH3$ .
Bond-line / skeletal formula: zig-zag line with 11 vertices.
Expanded formula with all C–H bonds shown (rarely needed).

Example Task (Undecane)

Asked: “Give a formula for undecane.”
- Molecular: $C{11}H{24}$ .
- Condensed: $CH3(CH2)9CH3$ .
- Skeletal: 11-vertex zig-zag line.
- Any one of the above is correct.

Helpful Tips & Common Pitfalls

Always look for the (aq) label; without water the compound is not named as an acid.
In oxoacids, ignore the number of hydrogens—focus on the anion name (-ate → ‑ic).
Cyanide is memorized as the single polyatomic exception that still uses the “hydro-” binary pattern.
Avoid mis-pronouncing 4-carbon roots: it is butane, not “but-ane” (video humor about “butt-anal”).
When counting carbons in line drawings, each corner or line end = one carbon (unless another element symbol is written).
For alkanes, hydrogens are assumed and often omitted in skeletal drawings—chemists rarely draw every H.

Quick Reference (Flash Cards)

Binary acid pattern: hydro + element-root + ic acid.
Ternary/oxoacid pattern: (polyatomic root w/ O) + ic acid.
Alkane formula: $CnH{2n+2}$ .
Carbon prefixes: meth–, eth–, prop–, but–, pent–, hex–, hept–, oct–, non–, dec–, (undec–, dodec–, …).

Ethical / Practical Notes

Safe handling: acids are corrosive; hydrocarbons are flammable—proper lab protocols are essential.
Environmental link: naming fuels correctly is foundational for discussions of combustion, pollution, and green chemistry.

Mini-Checklist Before the Exam

[ ] Distinguish gas vs aqueous forms of hydrogen halides.
[ ] Memorize required polyatomic ions (e.g., nitrate, sulfate, phosphate) and apply “-ic acid” rule.
[ ] Recall cyanide exception.
[ ] Master carbon prefixes up to at least 10.
[ ] Practice drawing and interpreting skeletal/condensed structures.
[ ] Verify alkane formulas with $CnH{2n+2}$ quickly.