Acids and redox


Acids, Bases and neutralisation

All acids contain hydrogen in their formula. When dissolved in water the acid dissociates into H+ ions and negative ions. A strong acid releases all of its H+ ions into the solvent, wheras a weak acid only partially dissociates. Most organic acids are weak acids. The equilibrium sign is used to show that the reaction is incomplete. Metal oxides, hydroxides, carbonates and ammonia are classified as bases. A base neutralises an acid to form a salt. An alkali is a base that can dissolve in water, releasing OH- ions into the solution. When acid is neutralised by metal carbonates or hydrocarbonates, the products are a salt and water. When an acid and alkali react in a solution, they dissociate before reacting. The ionic equation is H+(aq) + OH-(aq) --> H2O(l). When an acid is neutralised by a metal carbonate, the products are a salt, water, and carbon dioxide.

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Acid-Base titrations

Tritrations are used for finding the concentration of a solution, identification of unknown chemicals and finding the purity of a substance. A standard solution is a solution of known concentration. They are made up in volumetric flasks and the typical volumes of the flasks are 100cm3 +- 0.20cm3 and 250cm3 +- 0.30cm3. In a titration, the standard solution is titrated with use of other apperatus like pipettes, and a burette. The burette reading is measured to the nearest half division, because that is the only accurate way to measure it by sight. When working out the mean titre, only use concordant results and not the rough titration. With a tritration the concentration and volume of the standard solution is known as well as the volume for the unkown solution. The concentration can be worked out through calculations.

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