Making salts by neutralisation
When an acidCorrosive substance which has a pH lower than 7. Acidity is caused by a high concentration of hydrogen ions. reacts with a metal hydroxide (an alkaliA base which is soluble in water.), a saltA compound formed by neutralisation of an acid by a base, eg a metal oxide, as the result of hydrogen ions in the acid being replaced by metal ions or other positive ions. Sodium chloride, common salt, is one such compound. and water are produced:
acid + metal hydroxide \(\rightarrow\) salt + water
The name of a salt has two parts:
- the first part comes from the metal in the metal hydroxide
- the second part from the acid used
| Hydrochloric acid | Sulfuric acid | Nitric acid | |
| Potassium hydroxide | Potassium chloride | Potassium sulfate | Potassium nitrate |
| Sodium hydroxide | Sodium chloride | Sodium sulfate | Sodium nitrate |
| Calcium hydroxide | Calcium chloride | Calcium sulfate | Calcium nitrate |
| Potassium hydroxide | |
| Hydrochloric acid | Potassium chloride |
| Sulfuric acid | Potassium sulfate |
| Nitric acid | Potassium nitrate |
| Sodium hydroxide | |
| Hydrochloric acid | Sodium chloride |
| Sulfuric acid | Sodium sulfate |
| Nitric acid | Sodium nitrate |
| Calcium hydroxide | |
| Hydrochloric acid | Calcium chloride |
| Sulfuric acid | Calcium sulfate |
| Nitric acid | Calcium nitrate |
Question
Write a word equation to describe the reaction between hydrochloric acid and sodium hydroxide.
hydrochloric acid + sodium hydroxide \(\rightarrow\) sodium chloride + water
Formulae of salts
To work out the formulaA combination of symbols that indicates the chemical composition of a substance. of a salt you must know the charges of the ions involved.
| Common cations | Charge | Common anions | Charge |
| Hydrogen ion, H+ | +1 | Group 7 ions, e.g. Cl- | -1 |
| Ammonium ion, NH4+ | +1 | Hydroxide ion, OH- | -1 |
| Group 1 ions, eg K+, Na+ | +1 | Nitrate ion, NO3- | -1 |
| Group 2 ions, eg Mg2+, Ca2+ | +2 | Carbonate ion, CO32- | -2 |
| copper(II), Cu2+ | +2 | Carbonate ion, CO32- | -2 |
| Iron(II), Fe2+ | +2 | Sulfate ion, SO42- | -2 |
| Iron(III), Fe3+ | +3 |
| Common cations | Hydrogen ion, H+ |
|---|---|
| Charge | +1 |
| Common anions | Group 7 ions, e.g. Cl- |
| Charge | -1 |
| Common cations | Ammonium ion, NH4+ |
|---|---|
| Charge | +1 |
| Common anions | Hydroxide ion, OH- |
| Charge | -1 |
| Common cations | Group 1 ions, eg K+, Na+ |
|---|---|
| Charge | +1 |
| Common anions | Nitrate ion, NO3- |
| Charge | -1 |
| Common cations | Group 2 ions, eg Mg2+, Ca2+ |
|---|---|
| Charge | +2 |
| Common anions | Carbonate ion, CO32- |
| Charge | -2 |
| Common cations | copper(II), Cu2+ |
|---|---|
| Charge | +2 |
| Common anions | Carbonate ion, CO32- |
| Charge | -2 |
| Common cations | Iron(II), Fe2+ |
|---|---|
| Charge | +2 |
| Common anions | Sulfate ion, SO42- |
| Charge | -2 |
| Common cations | Iron(III), Fe3+ |
|---|---|
| Charge | +3 |
| Common anions | |
| Charge |
transition metalA metal that is located in between group 2 and group 3 (labelled as group 13 on some modern periodic tables) and has brightly coloured compounds. can form ions with different charges, eg iron can form Fe2+ ions and Fe3+ ions. Their charges are shown in the name of the compound, eg iron(II) oxide and iron(III) oxide.
The formula for a compound must produce no overall charge. For example:
- sodium hydroxide is NaOH (one positive charge and one negative charge)
- calcium hydroxide is Ca(OH)2 (two positive charges and two negative charges)
Question
What is the formula of sodium sulfate?
Na2SO4 (two positive charges and two negative charges)
Balanced chemical equations
To write a balanced chemical equationA chemical equation written using the symbols and formulae of the reactants and products, so that the number of units of each element present is the same on both sides of the arrow. first write the word equation. Replace the name of each compound with the correct formula.
massThe amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). is conserved during a chemical reaction. No atomThe smallest part of an element that can exist. are created or destroyed, so the numbers of atoms of each element on the left of the equation is the same as on the right. For example:
CuCO3(s) + H2SO4(aq) \(\rightarrow\) CuSO4(aq) + CO2(g) + H2O(l)
- copper sulfate is formed from Cu2+ ions in the metal carbonate and SO42- ions in the acid
- carbon dioxide and water are formed from H+ ions in the acid and CO32- ions in the metal carbonate
Question
Write a balanced chemical equation for the reaction of dilute sulfuric acid with sodium carbonate, Na2CO3.
H2SO4(aq) + Na2CO3(s) \(\rightarrow\) Na2SO4(aq) + CO2(g) + H2O(l)