Properties & Naming of Acids and Bases

• Sour taste (e.g. citric acid in lemons, acetic acid in vinegar).
• Turn blue litmus paper red.
• React with active metals (e.g. Zn, Mg) to release hydrogen gas.
• React with carbonates to release carbon dioxide gas (fizzing).
• Conduct electricity in aqueous solution (acids are electrolytes).
• Corrosive; can react with and dissolve certain materials.

• Bitter taste and a slippery, soapy feel (e.g. soap solutions).
• Turn red litmus paper blue.
• Conduct electricity in aqueous solution (bases are electrolytes).
• React with fats and oils (this is why bases are used in soap-making and some cleaning products).
• Corrosive at high concentrations, especially to skin and eyes.

Notice which properties the two groups SHARE and which are OPPOSITE. Both conduct electricity in water, because both produce ions when they dissolve. Their effects on litmus are opposite, and when an acid and a base are mixed in the right amounts they cancel each other's properties — a reaction called neutralization, which produces a salt and water. Some properties are one-sided: only acids fizz with carbonates (releasing ${\text{CO}}_2$) and with active metals such as zinc or magnesium (releasing ${\text{H}}_2$). That makes the carbonate test a fast, safe way to tell an acid from a base in the lab. Neutralization is also what an antacid does in the stomach, what farmers do when they spread lime on acidic soil, and what water treatment plants do when they raise the pH of acidic water so it will not corrode lead or copper pipes. Ontario's operational guideline for drinking water is a pH between 6.5 and 8.5.

A binary acid is made of hydrogen plus one other nonmetal element (no oxygen). The naming pattern is: hydro- + (root of the nonmetal) + -ic acid. The state symbol matters: pure $\text{HCl(g)}$ is a molecular gas called hydrogen chloride, and it only behaves as an acid once it is dissolved in water, so $\text{HCl(aq)}$ is hydrochloric acid. The acid names apply to the aqueous solution. The first step in naming any acid is therefore to look for oxygen: no oxygen means a binary acid (hydro-...-ic); oxygen present in a polyatomic ion means an oxyacid (no hydro- prefix).

An oxyacid is hydrogen combined with a polyatomic (often oxygen-containing) ion. The name comes directly from the polyatomic ion's name, following a predictable suffix pattern: an ion ending in -ate becomes an acid ending in -ic acid; an ion ending in -ite becomes an acid ending in -ous acid. A memory aid: 'I ate something ic-ky' (-ate → -ic) and 'the bite was delicious' (-ite → -ous). Any prefix on the ion carries straight over: perchlorate (${\text{ClO}}_4^{-}$) gives perchloric acid, ${\text{HClO}}_4$, and hypochlorite (${\text{ClO}}^{-}$) gives hypochlorous acid, $\text{HClO}$ — the active disinfectant formed when chlorine is added to drinking water. The number of H atoms in the formula equals the size of the ion's negative charge, because the acid is neutral: sulfate is $2-$, so sulfuric acid is ${\text{H}}_2{\text{SO}}_4$; phosphate is $3-$, so phosphoric acid is ${\text{H}}_3{\text{PO}}_4$. Sulfur and phosphorus keep a longer root in their acid names (sulfuric, phosphoric) because it sounds better.

Common bases are metal hydroxides, and they're named exactly like any other ionic compound: metal name, then 'hydroxide.' For metals with variable charge, a Roman numeral indicates the charge, just as in regular ionic nomenclature. To write a formula from the name, balance the charges: calcium is $2+$ and hydroxide is $1-$, so two hydroxides are needed and the formula is ${\text{Ca(OH)}}_2$, with brackets around the polyatomic ion. Only the Group 1 hydroxides (and barium hydroxide) dissolve well, so they give strongly basic solutions; hydroxides such as ${\text{Mg(OH)}}_2$ dissolve so little that a suspension of it is gentle enough to swallow as an antacid.