Exchange Reactions:
Exchange reactions involve the exchange of ions between compounds. Specific examples of these are precipitation reactions. In these two soluble compounds exchange ions, based on the reactivity series, to produce a soluble and an insoluble compound. The insoluble compound will come out of solution, as it forms and be seen as a precipitate.
The solubility rules (below), along with the reactivity series, will help in making predictions on whether a precipitate is formed or not.
The solubility rules (below), along with the reactivity series, will help in making predictions on whether a precipitate is formed or not.
Soluble or not?
Substances are defined as soluble when 1g or more of the substance will dissolve in 100ml of water at 25 C. Substances are defined as insoluble when less than 0.1g of the substance will dissolve in 100ml of water at 25 C. Some substances are defined as sparingly soluble when between 0.1g and 1g will dissolve.
A precipitate is an insoluble substance formed when two soluble substances in solutions are mixed.
A precipitate is an insoluble substance formed when two soluble substances in solutions are mixed.
Solubility Rules!
- Nitrates are all soluble.
- Chlorides are all soluble except silver chloride and lead chloride.
- Sulfates are all soluble except lead sulfate, calcium sulfate and barium sulfate.
- Carbonates are all insoluble except those of Group 1 (sodium carbonate and potassium carbonate) and ammonium carbonate.
- Hydroxides are all insoluble except those of Group 1 (sodium hydroxide and potassium hydroxide) and ammonium hydroxide
Examples:Sodium chloride and silver nitrate → sodium nitrate and silver chloride
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s) Silver Chloride is insoluble and forms a precipitate. Sodium Sulphate and Barium Nitrate → Sodium Nitrate and Barium Sulphate Na₂SO₄(aq) + Ba(NO₃)₂ (aq) ---> BaSO₄(s) + 2NaNO₃(aq) Sulphates are usually soluble, however, as we saw in the solubility rules Barium Sulphate is an exception to this rule. |
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