Ad
related to: strong acid vs weak diagram definition science examples for kids
Search results
Results From The WOW.Com Content Network
For example, acetic acid is a weak acid which has a = 1.75 x 10 −5. Its conjugate base is the acetate ion with K b = 10 −14 /K a = 5.7 x 10 −10 (from the relationship K a × K b = 10 −14), which certainly does not correspond to a strong base. The conjugate of a weak acid is often a weak base and vice versa.
For example, if the concentration of the conjugate base is 10 times greater than the concentration of the acid, their ratio is 10:1, and consequently the pH is pK a + 1 or pK b + 1. Conversely, if a 10-fold excess of the acid occurs with respect to the base, the ratio is 1:10 and the pH is p K a − 1 or p K b − 1.
An example of an alkalimetric titration involving a strong acid is as follows: H 2 SO 4 + 2 OH − → SO 4 2-+ 2 H 2 O. In this case, the strong acid (H 2 SO 4) is neutralized by the base until all of the acid has reacted. This allows the viewer to calculate the concentration of the acid from the volume of the standard base that is used.
Acetic acid is an example of a weak acid. The pH of the neutralized solution resulting from HA + OH − → H 2 O + A −. is not close to 7, as with a strong acid, but depends on the acid dissociation constant, K a, of the acid. The pH at the end-point or equivalence point in a titration may be calculated as follows.
However, for weak acids, a quadratic equation must be solved, and for weak bases, a cubic equation is required. In general, a set of non-linear simultaneous equations must be solved. Water itself is a weak acid and a weak base, so its dissociation must be taken into account at high pH and low solute concentration (see Amphoterism).
A weak acid may be defined as an acid with pK a greater than about −2. An acid with pK a = −2 would be 99 % dissociated at pH 0, that is, in a 1 M HCl solution. Any acid with a pK a less than about −2 is said to be a strong acid. Strong acids are said to be fully dissociated.
However, the acids and bases must differ greatly in strength, e.g. one strong acid and one very weak acid. [1] Therefore, the two acids must have a pK a (or pK b) difference that is as large as possible. For example, the following can be separated: Very weak acids like phenols (pK a around 10) from stronger acids like carboxylic acids [1] (pK a ...
The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form hydronium ion (H 3 O +). [2] An example of this would be the following reaction, where "HA" is the strong acid: