Typical Reactions Involving Acids

Typical Reactions Involving Acids

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One of the ways acids were originally classified was by their characteristic reactions. Did they react with metals and if they did were there consistent observations? Did they do anything interesting when an alkali was dropped in them? Over time folks who liked to watch for these things drew certain conclusions, of which the following are deemed to be particularly important:

* acid plus metal produces salt plus hydrogen gas

* acid plus metal hydroxide produces salt and water

* acid plus metal oxide also produces salt and water

* acid plus metal carbonate produces salt, carbon dioxide gas and water

* acid plus metal hydrogen carbonate also produces salt, carbon dioxide gas and water

* acid plus metal sulfite produces salt, sulfur dioxide gas and water.

You might like to note that the reactions above are generic and ignore the fact that 'oxidising acids' notably concentrated sulfuric and nitric acids, react with metal to give much more interesting products. For example, concentrated nitric acid reast with copper metal to give salt, water AND a particularly unfriendly gas, N2O4.

In the above discussion the term salt has occurred several times; it is not, of course, referring solely to NaCl, so called table salt. In this context the term salt refers to any ionic compound resulting from a reaction involving acids. So if you mix solutions of HCl and NaOH you get aqueous NaCl and HOH (or H2O). NaCl is the salt. On the other hand, if you mix HNO3 and CuO you get Cu(NO3)2 and H2O. In this case Cu(NO3)2 is the salt.

As it turns out, each of the typical reactions listed above follows a pattern, as set out in this table. In all cases the resulting salt is CuCl2(aq).

metal or compound | example |

pure metal | Cu(s) + 2HCl(aq) → CuCl2(aq) + H2(g) |

hydroxide | Cu(OH)2(s) + 2HCl(aq) → CuCl2(aq) + 2H2O(g) |

oxide | CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(g) |

carbonate |