Salts
Salts are ionic compounds made of positive ions and negative acid-residue ions. Charge balance determines formulas, while solubility and reactivity determine many properties and preparation methods.
Learning goals
- Construct and name salt formulas.
- Use solubility information to predict precipitates.
- Describe reactions with metals, acids, bases, and other salts.
- Select suitable preparation routes.
Formula and name
Total positive and negative charge must be zero. Ca2+ needs two Cl−, giving CaCl2; Al3+ needs three NO3−, giving Al(NO3)3. Name the cation first and the acid-residue anion second. For variable-charge metals include a Roman numeral: FeCl2 is iron(II) chloride.
| Anion | Name | Example salt |
|---|---|---|
| Cl− | chloride | NaCl |
| SO42− | sulfate | K2SO4 |
| NO3− | nitrate | Ca(NO3)2 |
| CO32− | carbonate | CaCO3 |
Properties and reactions
| Pattern | Condition | Example |
|---|---|---|
| salt + salt | precipitate forms | $BaCl_2+Na_2SO_4\rightarrow BaSO_4\downarrow+2NaCl$ |
| salt + base | insoluble hydroxide forms | $CuSO_4+2NaOH\rightarrow Cu(OH)_2\downarrow+Na_2SO_4$ |
| salt + acid | gas, precipitate, or weak product forms | $Na_2CO_3+2HCl\rightarrow2NaCl+H_2O+CO_2\uparrow$ |
| metal + salt | more active metal displaces less active one | $Fe+CuSO_4\rightarrow FeSO_4+Cu$ |
Ion exchange is not automatically a reaction. In aqueous solution it proceeds when a precipitate, gas, or weakly ionized product such as water is formed.
Preparation routes
- Neutralization: acid + base → salt + water.
- Acid + basic oxide, or base + acidic oxide.
- Direct combination of suitable elements.
- Precipitation from two soluble solutions for an insoluble salt.