Types of bases Bases - feel slippery and soapy → used in many cleaning products. Weak bases → used as window cleaners. Strong bases → able to dissolve grease and protein and are used for cleaning drains and ovens. Must be handled with care to prevent solution from reacting with skin.
Definition
Base is any metal oxide or hydroxide which reacts with acid to produce salt and water. They contain either oxide ion (O2-) or hydroxide ion (OH-)
Classification of bases:
- Metal oxides: eg copper oxide
- Metal hydroxides: eg sodium hydroxide
- Aqueous ammonia
Bases are ionic compounds*
| bases | formula |
| Sodium oxide | Na2O |
| Zinc oxide | ZnO |
| copper(II)oxide | CuO |
| Magnesium hydroxide | Mg(OH)2 |
| Aluminum hydroxide | Al(OH)3 |
Physical properties of bases
- Bases have high melting and boiling points (non volatile)
- The natural physical states of bases at r.t.p is solid state
- Metal hydroxides which are soluble in water can also be in aqueous state
- Answering techniques: refer to Ionic Compounds, Properties of Ionic Compounds
List of soluble bases: (all group 1 elements and last 4 group 2 elements)
| Group 1 metal oxides | Group 1 metal hydroxides | Group 2 metal oxides | Group 2 metal hydroxides |
| Lithium oxide (Li2O) | Lithium hydroxide (LiOH) | Calcium oxide (CaO) | Calcium hydroxide (Ca(OH)2) |
| Sodium oxide (Na2O) | Sodium hydroxide (NaOH) | Strontium oxide (SrO) | Strontium hydroxide (Sr(OH)2) |
| Potassium oxide (K2O) | Potassium hydroxide (KOH) | Barium oxide (BaO) | Barium hydroxide (Ba(OH)2) |
| Rubidium oxide (Rb2O) | Rubidium hydroxide (RbOH) | Radium oxide (RaO) | Radium hydroxide (Ra(OH)2) |
| Caesium oxide (Cs2O) | Caesium hydroxide (CsOH) | ||
| Aqueous ammonia as well! (NH3) |
Water soluble base + water (water soluble base: Alkalis)
- Metal oxides react with water to form aqueous solution of corresponding metal hydroxides
- General equation
- Water-soluble metal oxide(s) + water → water (l) + metal hydroxide solution (aq)
- Solid metal hydroxides dissolve in water to form aqueous solution of metal hydroxides
Metal oxides react with water to form aqueous solution of corresponding metal hydroxides. ⇒ thus this means that there would never be a metal oxide solution existing.
Bases are good conductors of electricity when molten and in aqueous solutions
- Same explanation as ionic compounds as bases are ionic compounds (Ionic Compounds, Properties of Ionic Compounds)
Bases + Acids → Salt + Water
i) Metal oxide + dilute acid ⇒ salt + water ii) metal hydroxide + dilute acid ⇒ salt + water
Known as neutralization reaction