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Line 1: − + − + − + − + − + − + − The end result being:+ − + − However, not all neutralisation reactions involve the reactants dissociating, ammonia (NH<sub>3</sub>) is a base which will accept a proton to form ammonium, and hence will undergo an acid-base reaction in its pure form, for example:+ − + − + − Line 35:
Line 34: − + − + − As the iron hydroxide is a weak base it will not dissociate to any great extent and hence will not raise the pH of the water greatly, however this hydrolysis reaction causes an excess of hydrogen ions, which result in the pH of the water being lowered hence causing it to be acidic. As the chloride ion is a weak base it will not react with water, hence producing an acidic salt.+ Line 49:
Line 48: − '''[[Titration]]''' - a volumetric analysis of acids/bases to determine an unknown concentration. As the acids/bases neutralise they will cause an ongoing change in pH of the solution producing a characteristic titration curve. This can be used to determine when equal [[moles]] of acid and base were added to the reaction vessel, which can in turn be used to determine the unknown concentration.+ − + − '''Chemical Spills''' - strong acids and bases can be harmful to the environment, hence they must be neutralised as soon as possible. The most commonly used neutralising agent is sodium bicarbonate (NaHCO<sub>3</sub>) as it is amphiprotic (hence can act as either an acid or a base, and can be used on either species). Often the reaction is covered with sand to prevent excess thermal pollution − − ==See Also== − − * [[Acid]] − * [[Base]] − * [[Titration]]
general clean up
An '''acid base reaction''' is a proton transfer reaction between an [[acid]] (a proton donor) and a [[base]] (a proton acceptor). It is also known as a neutralisation reaction and it exothermic (releases heat energy). In general, the products of an acid-base reaction are a salt and water.
An '''acid-base reaction''', also known as a neutralization reaction, is a [[proton]] transfer reaction between an [[acid]] (a ''proton donor'') and a [[base]] (a ''proton acceptor''). In general, acid-base reactions are typically exothermic and they produce [[salt]] and [[water]].
==General Chemistry==
==General Chemistry==
In a majority of cases, the acid and base regents will dissociate to form ions which take part in the reaction mechanism and those which form the salt. For instance, in the reaction between hydrochloric acid and sodium hydroxide:
In a majority of cases, the acid and base regents will [[dissociation|dissociate]] to form [[ion]]s which take part in the reaction mechanism and those which form the salt. For instance, in the aqueous reaction between hydrochloric acid and sodium hydroxide:
HCl<sub>(aq)</sub> -- H<sup>+</sup><sub>(aq)</sub> + Cl<sup>-</sup><sub>(aq)</sub>
:HCl <math>\rightleftharpoons</math> H<sup>+</sup> + Cl<sup>-</sup>
NaOH<sub>(aq)</sub> -- Na<sup>+</sup><sub>(aq)</sub> + OH<sup>-</sup><sub>(aq)</sub>
:NaOH <math>\rightleftharpoons</math> Na<sup>+</sup> + OH<sup>-</sup>
Some of these ions will then partake in the proton transfer reaction, such that:
Some of these ions will then partake in the proton transfer reaction, such that:
H<sup>+</sup><sub>(aq)</sub> + OH<sup>-</sup><sub>(aq)</sub> -- H<sub>2</sub>O<sub>(l)</sub>
:H<sup>+</sup> + OH<sup>-</sup> <math>\rightleftharpoons</math> H<sub>2</sub>O
The remaining ions will form a salt, such that:
The remaining ions will form a salt, such that:
Na<sup>+</sup><sub>(aq)</sub> + Cl<sup>-</sup><sub>(aq)</sub> -- NaCl<sub>(aq)</sub>
:Na<sup>+</sup> + Cl<sup>-</sup> <math>\rightleftharpoons</math> NaCl<sub>(aq)</sub>
Thus the overall reaction is:
HCl<sub>(aq)</sub> + NaOH<sub>(aq)</sub> -- H<sub>2</sub>O<sub>(l)</sub> + NaCl<sub>(aq)</sub>
:HCl<sub>(aq)</sub> + NaOH<sub>(aq)</sub> <math>\rightleftharpoons</math> H<sub>2</sub>O<sub>(l)</sub> + NaCl<sub>(aq)</sub>
In this case the salt will remain in aqueous (dissolved) form, however if it was insoluble it would precipitate out of the water.
In this case the salt will remain in aqueous (dissolved) form, however if it was insoluble it would precipitate out of the water.
Not all neutralisation reactions involve the reactants dissociating. For example, [[ammonia]] (NH<sub>3</sub>) is a base which will accept a proton to form [[ammonium]], and hence will undergo an acid-base reaction in its pure form, for example:
NH<sub>3(aq)</sub> + H<sup>+</sup><sub>(aq)</sub> -- NH<sub>4</sub><sup>+</sup><sub>(aq)</sub>
:NH<sub>3(aq)</sub> + H<sup>+</sup><sub>(aq)</sub> <math>\rightleftharpoons</math> NH<sub>4</sub><sup>+</sup><sub>(aq)</sub>
==Acidity of the Salt==
==Acidity of the Salt==
The salt which forms may have a [[pH]] of its own due due to its components being [[conjugate acid]]s and [[conjugate base]]s. The conjugate acid of a [[strong base]] and the conjugate base of a [[strong acid]] are weak, and hence will not dissociate. However, the conjugates of weak acids/bases are strong bases/acids, and hence will undergo a hydrolysis reaction with water to form and acid/base. The general rule is:
The salt which forms may have a [[pH]] of its own due due to its components being [[conjugate acid]]s and [[conjugate base]]s. The conjugate acid of a strong base and the conjugate base of a strong acid are weak, and hence will not dissociate. However, the conjugates of weak acids/bases are strong bases/acids, and hence will undergo a hydrolysis reaction with water to form and acid/base. The general rule is:
*A strong acid and a strong base will form a neutral salt
*A strong acid and a strong base will form a neutral salt
*A strong acid and a weak base will form an acidic salt (will react with water to form an acid)
*A strong acid and a weak base will form an acidic salt (will react with water to form an acid)
For instance, a strong acid and weak base reaction may proceed as such:
For instance, a strong acid and weak base reaction may proceed as such:
2HCl<sub>(aq)</sub> + Fe(OH)<sub>2(aq)</sub> -- 2H<sub>2</sub>O<sub>(l)</sub> + FeCl<sub>2(aq)</sub>
:2HCl + Fe(OH)<sub>2</sub><math>\rightleftharpoons</math> 2H<sub>2</sub>O + FeCl<sub>2</sub>
The iron component of the iron chloride may then undergo a hydrolysis reaction with water, such that:
The iron component of the iron chloride may then undergo a hydrolysis reaction with water, such that:
Fe<sup>2+</sup> + H<sub>2</sub>O<sub>(l)</sub> -- Fe(OH)<sub>2(aq)</sub> + H<sup>+</sup><sub>(aq)</sub>
:Fe<sup>2+</sup> + H<sub>2</sub>O <math>\rightleftharpoons</math> Fe(OH)<sub>2</sub> + H<sup>+</sup>
Since the iron hydroxide is a weak base, it will not dissociate to any great extent and hence will not raise the pH of the water greatly. However, this hydrolysis reaction causes an excess of hydrogen ions, which result in the pH of the water being lowered, hence causing it to be acidic. As the chloride ion is a weak base it will not react with water, producing an acidic salt.
The same process applies for basic salts, however the products will contain an excess of OH<sup>-</sup> and a weak acid, causing the water to become basic.
The same process applies for basic salts, however the products will contain an excess of OH<sup>-</sup> and a weak acid, causing the water to become basic.
There are several uses of acid-base neutralisation reactions.
There are several uses of acid-base neutralisation reactions.
*''[[Titration]]'': a [[volume]]tric analysis of acids and bases to determine an unknown concentration. As the acids/bases neutralise they will cause an ongoing change in pH of the solution producing a characteristic titration curve. This can be used to determine when equal [[mole]]s of acid and base were added to the reaction vessel, which can in turn be used to determine the unknown concentration.
*''Chemical spills'': strong acids and bases can be harmful to the environment and should be neutralised as soon as possible. The most commonly used neutralising agent is sodium bicarbonate (NaHCO<sub>3</sub>) as it is [[amphiprotic]] (it can act as either an acid or a base).
[[Category:Chemistry]]
[[Category:Chemistry]]