Naming Salts from Their Parent Acids

“What salt is made when magnesium reacts with sulfuric acid?” is one of the most common questions in introductory chemistry. The answer, magnesium sulfate, follows a simple two-part pattern. Once you know which acid produces which ending, you can name hundreds of salts without memorising them individually.

The rule

A salt’s name has two parts:

1. First word: the cation, usually a metal (or ammonium). It comes from the base, metal, oxide or carbonate.
2. Second word: the anion. It comes from the acid, and each acid gives a characteristic ending.

metal + acid → metal acid-ending

So in “magnesium sulfate”, magnesium comes from the metal and sulfate from sulfuric acid.

Which acid gives which name

Acid	Formula	Salt ending	Anion	Example salt
Hydrochloric acid	HCl	chloride	Cl⁻	sodium chloride, NaCl
Sulfuric acid	H₂SO₄	sulfate	SO₄²⁻	copper(II) sulfate, CuSO₄
Nitric acid	HNO₃	nitrate	NO₃⁻	potassium nitrate, KNO₃
Phosphoric acid	H₃PO₄	phosphate	PO₄³⁻	calcium phosphate, Ca₃(PO₄)₂
Carbonic acid	H₂CO₃	carbonate	CO₃²⁻	sodium carbonate, Na₂CO₃
Ethanoic (acetic) acid	CH₃COOH	ethanoate (acetate)	CH₃COO⁻	sodium ethanoate, CH₃COONa
Hydrobromic acid	HBr	bromide	Br⁻	potassium bromide, KBr
Hydroiodic acid	HI	iodide	I⁻	silver iodide, AgI
Hydrofluoric acid	HF	fluoride	F⁻	sodium fluoride, NaF
Methanoic (formic) acid	HCOOH	methanoate (formate)	HCOO⁻	calcium methanoate
Citric acid	C₆H₈O₇	citrate	C₆H₅O₇³⁻	sodium citrate
Sulfurous acid	H₂SO₃	sulfite	SO₃²⁻	sodium sulfite, Na₂SO₃
Nitrous acid	HNO₂	nitrite	NO₂⁻	sodium nitrite, NaNO₂

The big four for most exams are the first four: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate, phosphoric → phosphate. Add carbonic → carbonate and ethanoic → ethanoate and you’ve covered almost every question.

Patterns in the endings

• Binary acids (hydrogen + one non-metal, named hydro-…-ic acid) give salts ending in -ide: hydrochloric → chloride.
• Oxyacids ending in -ic give salts ending in -ate: sulfuric → sulfate, nitric → nitrate.
• Oxyacids ending in -ous give salts ending in -ite: sulfurous → sulfite, nitrous → nitrite.

A memory line some students like: “-ic acids make -ate salts; -ous acids make -ite salts”. For more on these endings, see how to name ionic compounds.

Naming the cation

Group 1 and Group 2 metals, aluminium and zinc have only one common charge, so the metal’s name is used unchanged: sodium, potassium, magnesium, calcium, aluminium, zinc.

Transition metals (and a few others, such as tin and lead) can form ions with different charges, so the charge is shown with a Roman numeral in brackets:

• FeSO₄ → iron(II) sulfate (Fe²⁺)
• Fe₂(SO₄)₃ → iron(III) sulfate (Fe³⁺)
• CuCl → copper(I) chloride (Cu⁺)
• CuCl₂ → copper(II) chloride (Cu²⁺)
• PbCl₂ → lead(II) chloride

To work out the numeral, balance the charges. In Fe₂(SO₄)₃, three sulfates give 3 × (−2) = −6, shared between two iron ions, so each iron is +3.

Ammonium salts use the name ammonium for NH₄⁺, which behaves just like a metal ion: ammonium chloride, ammonium nitrate, ammonium sulfate.

Predicting the salt from a reaction

Example 1. Zinc + hydrochloric acid → ? Zinc gives zinc; hydrochloric acid gives chloride. Zinc chloride, ZnCl₂ (plus hydrogen gas).

Example 2. Copper(II) oxide + sulfuric acid → ? Copper(II) gives copper(II); sulfuric acid gives sulfate. Copper(II) sulfate, CuSO₄ (plus water).

Example 3. Calcium carbonate + nitric acid → ? Calcium nitrate, Ca(NO₃)₂ (plus water and carbon dioxide).

Example 4. Potassium hydroxide + phosphoric acid (fully neutralised) → ? Potassium phosphate, K₃PO₄ (plus water).

Example 5. Ammonia + sulfuric acid → ? Ammonium sulfate, (NH₄)₂SO₄. This is a major fertiliser.

Example 6. Sodium hydroxide + ethanoic acid → ? Sodium ethanoate, CH₃COONa (plus water).

Writing the formula

The name tells you the ions; balance their charges to get the formula.

1. Write the ions with their charges: Al³⁺ and SO₄²⁻.
2. Find the lowest numbers that make the total charge zero: 2 × (+3) = +6 and 3 × (−2) = −6.
3. Write the formula, with brackets around polyatomic ions when there’s more than one: Al₂(SO₄)₃.

The “criss-cross” shortcut (swap the charge numbers to become subscripts) gives the same answer, but always simplify: Mg²⁺ and O²⁻ give MgO, not Mg₂O₂. A list of common ion charges is in polyatomic ions list.

Hydrogen salts (acid salts)

Acids with more than one acidic hydrogen can be partly neutralised, leaving a hydrogen in the anion. These salts include “hydrogen” in the name:

Formula	Name	Older or common name
NaHSO₄	sodium hydrogensulfate	sodium bisulfate
NaHCO₃	sodium hydrogencarbonate	sodium bicarbonate, baking soda
KH₂PO₄	potassium dihydrogenphosphate	monopotassium phosphate
Na₂HPO₄	sodium hydrogenphosphate	disodium phosphate
Ca(HCO₃)₂	calcium hydrogencarbonate	calcium bicarbonate (only exists in solution)

The prefix “bi-” in older names like bicarbonate means “hydrogen”, not “two”. IUPAC recommends the “hydrogen” names.

Hydrated salts

If a salt contains water of crystallisation, the name says how much using Greek prefixes:

• CuSO₄·5H₂O: copper(II) sulfate pentahydrate
• MgSO₄·7H₂O: magnesium sulfate heptahydrate
• Na₂CO₃·10H₂O: sodium carbonate decahydrate
• CaCl₂·2H₂O: calcium chloride dihydrate

If there’s no water, the salt can be called anhydrous: anhydrous copper(II) sulfate.

Common and trade names

Everyday life is full of older names for salts. It’s worth recognising them:

Common name	Chemical name	Formula
Table salt	sodium chloride	NaCl
Baking soda	sodium hydrogencarbonate	NaHCO₃
Washing soda	sodium carbonate decahydrate	Na₂CO₃·10H₂O
Epsom salts	magnesium sulfate heptahydrate	MgSO₄·7H₂O
Saltpetre	potassium nitrate	KNO₃
Chalk, limestone, marble	calcium carbonate	CaCO₃
Gypsum	calcium sulfate dihydrate	CaSO₄·2H₂O
Blue vitriol	copper(II) sulfate pentahydrate	CuSO₄·5H₂O
Sal ammoniac	ammonium chloride	NH₄Cl

Salts of organic acids

The same pattern works for acids from organic chemistry. Replace the “-ic acid” ending with “-ate”, and put the metal first:

• ethanoic acid → sodium ethanoate (often still called sodium acetate)
• propanoic acid → calcium propanoate (a bread preservative, E282)
• benzoic acid → sodium benzoate (a soft-drink preservative, E211)
• citric acid → sodium citrate or potassium citrate
• lactic acid → calcium lactate

You’ll see these names on food labels constantly. Reading “potassium sorbate” and recognising it as the potassium salt of sorbic acid is exactly the skill this article teaches.

Practice questions

Name the salt formed in each reaction:

1. Magnesium + sulfuric acid
2. Sodium hydroxide + nitric acid
3. Potassium carbonate + hydrochloric acid
4. Iron(III) oxide + hydrochloric acid
5. Ammonia + phosphoric acid (fully neutralised)

Write the formula for:

6. Calcium chloride
7. Aluminium nitrate
8. Sodium sulfate
9. Copper(II) ethanoate
10. Ammonium carbonate

Answers

1. Magnesium sulfate, MgSO₄
2. Sodium nitrate, NaNO₃
3. Potassium chloride, KCl
4. Iron(III) chloride, FeCl₃
5. Ammonium phosphate, (NH₄)₃PO₄
6. CaCl₂
7. Al(NO₃)₃
8. Na₂SO₄
9. (CH₃COO)₂Cu, often written Cu(CH₃COO)₂
10. (NH₄)₂CO₃

Common mistakes

• “Sulfide” for sulfuric acid salts. Sulfuric acid gives sulfate (SO₄²⁻). Sulfide (S²⁻) comes from hydrogen sulfide.
• “Chlorate” for hydrochloric acid salts. Hydrochloric acid gives chloride; chlorate (ClO₃⁻) comes from chloric acid.
• Forgetting the Roman numeral for transition metals.
• Missing brackets in formulas with more than one polyatomic ion: Ca(NO₃)₂, not CaNO₃₂.

Key takeaways

• Salt name = cation name + anion name from the acid.
• Hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate, phosphoric → phosphate, carbonic → carbonate, ethanoic → ethanoate.
• -ic acids give -ate salts; -ous acids give -ite salts; hydro-…-ic acids give -ide salts.
• Transition metal charges go in Roman numerals; partly neutralised salts include “hydrogen”.
• For what salts actually are, see what is a salt?.