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On the other hand, if a chemical is a weak acid its conjugate base will not necessarily be strong. Consider that ethanoate, the conjugate base of ethanoic acid, has a base splitting constant (Kb) of about 5.6 × 10 −10, making it a weak base. In order for a species to have a strong conjugate base it has to be a very weak acid, like water.
The removal of H + from the HCl produces the chloride ion, Cl −, the conjugate base of the acid. The addition of H + to the H 2 O (acting as a base) forms the hydronium ion, H 3 O +, the conjugate acid of the base. Water is amphoteric – that is, it can act as both an acid and a base.
The following reaction represents the general reaction between a base (B) and water to produce a conjugate acid (BH +) and a conjugate base (OH −): [3] + + + The equilibrium constant, K b, for this reaction can be found using the following general equation: [3]
Acetic acid, CH 3 COOH, is an acid because it donates a proton to water (H 2 O) and becomes its conjugate base, the acetate ion (CH 3 COO −). H 2 O is a base because it accepts a proton from CH 3 COOH and becomes its conjugate acid, the hydronium ion, (H 3 O +). [9]
For aqueous solutions of an acid HA, the base is water; the conjugate base is A − and the conjugate acid is the hydronium ion. The Brønsted–Lowry definition applies to other solvents, such as dimethyl sulfoxide: the solvent S acts as a base, accepting a proton and forming the conjugate acid SH +.
For buffers in acid regions, the pH may be adjusted to a desired value by adding a strong acid such as hydrochloric acid to the particular buffering agent. For alkaline buffers, a strong base such as sodium hydroxide may be added. Alternatively, a buffer mixture can be made from a mixture of an acid and its conjugate base.
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.
A conjugate base is formed when the acid is deprotonated by the base. In the image above, hydroxide acts as a base to deprotonate the carboxylic acid. The conjugate base is the carboxylate salt. In this case, hydroxide is a strong enough base to deprotonate the carboxylic acid because the conjugate base is more stable than the base because the ...