BBC Bitesize - KS3 Chemistry - Acids and bases - Revision 2
Not all metal oxides MxOy and metal hydroxides Mx(OH)y are basic. of them are amphoteric, which means that they can act as acid or base. Example of simple bases are sodium hydroxide and ammonia. Examples are oxides and hydroxides of heavy metals. . or pKb is a measure of basicity and related to the pKa by the simple relationship pKa + pKb = them. Bases are usually: metal oxides, such as copper oxide; metal hydroxides, such as sodium hydroxide, or; metal carbonates, such as calcium carbonate.
To understand why nonmetal hydroxides are acids and metal hydroxides are bases, we have to look at the electronegativities of the atoms in these compounds. Let's start with a typical metal hydroxide: As a result, the electrons in the Na O bond are not shared equally these electrons are drawn toward the more electronegative oxygen atom.
We get a very different pattern when we apply the same procedure to hypochlorous acid, HOCl, a typical nonmetal hydroxide. As a result, the electrons in the Cl O bond are shared more or less equally by the two atoms.
There is no abrupt change from metal to nonmetal across a row or down a column of the periodic table. We should therefore expect to find compounds that lie between the extremes of metal and nonmetal oxides, or metal and nonmetal hydroxides. These compounds, such as Al2O3 and Al OH 3, are called amphoteric literally, "either or both" because they can act as either acids or bases.
Al OH 3, for example, acts as an acid when it reacts with a base. The hydroxides of feebly acidic cations are not deliquescent.
Acids, bases, pH, and buffers
The oxides of weakly acidic cations and moderately acidic cations are insoluble in water. These oxides do not introduce significant amounts of O2- ion into the solution so hydroxide ions are not produced.
Although these oxides do not significantly alter the pH of the water, they are still bases and neutralize strong acids. Many of these oxides dissolve in water to give the oxo anion in which the element has the same oxidation number as the oxide. The oxide will be soluble if its reaction with water produces a strong or very strong acid because these acids ionize completely shifting the equilibrium toward dissolution. If the reaction with water produces a moderately acidic oxoacid, the oxide may or may not be soluble.
If the oxoacid generated is weakly acidic, the oxide is usually but not always insoluble in water.
These are frequently referred to as " Lewis acids  " and " Lewis bases  ," and are electrophiles  and nucleophiles respectively, in organic chemistry ; Lewis bases are also ligands in coordination chemistry. Lewis acids include substances with no transferable protons i. The Lewis definition can also be explained with molecular orbital theory.
This definition was developed by Gilbert N.
pH Scale: Acids, bases, pH and buffers (article) | Khan Academy
General properties Some general properties of bases include: Bitter taste opposed to sour taste of acids and sweetness of aldehydes and ketones Touch: Slimy or soapy feel on fingers Reactivity: Caustic  on organic matter, react violently with acidic or reducible substances Electric conductivity: Aqueous solutions or molten bases dissociate in ions and conduct electricity Litmus test: Bases turn red litmus paper blue.
The pH of impure water is a measure of its acidity. Both actions will lower the concentration of hydronium ions, and thus raise pH.
Base Strenght A "Strong Base" is one which hydrolyzes completely, deprotonating acids in an acid-base reaction, hence, raising the pH of the solution towards Compounds with a pH of more than about 13 are called strong bases.
Strong bases, like strong acids, attack living tissue and cause serious burns. They react differently to skin than acids do so while strong acids are corrosive, we say that strong bases are caustic.