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Unformatted text preview: suggested by the size of the respective arrows) and only a few carbonic acid molecules (H2CO3) are converted to bicarbonate ions HCO3 ─ ). +
The concentration of hydrogen ion, H , produced by dissolving a given amount of weak acid is much less than if the same amount of strong acid is dissolved. A similar situation exists with bases. Some substances, which do not contain hydroxide ─
ions, OH in pure form, produce hydroxide ions, OH , in water by reacting with the water. The most important example of this kind of base is ammonia gas, NH3. +
Ammonia produces OH ions by taking H ions from water molecules and leaving OH ions behind: +
H NH3(g) + H2O(l) ammonia water partial dissociation ─
< ─────────────── NH4 + (aq) + OH (aq) ──> ammonium ion hydroxide ion (ammonium hydroxide) This equilibrium also lies well to the left, meaning that the majority of particles present in an aqueous solution of ammonia are NH3 molecules and very few ammonium ions, NH4+ ─
and hydroxide ions, OH , are present. In a 1 M solution of NH3 in water, only about 4 molecules of NH3 out of every 1000 have reacted to form NH4+ ions. Nevertheless, some ─
OH ions are produced, so an aqueous solution of NH3 is in fact a base, although a weak one. Substances that produce OH by partial dissociation are called weak bases....
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