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This model illustrates the process of titration of buffer solutions. Buffer solutions are used for creation of media having certain pH value, resistant to slight additions of acid or alkali. Buffer solution consists of either weak acid with its salt, or weak base and its salt.
At the left bottom of the model, the list of buffer solutions proposed for study is presented. Some of these provide acid media and some others - alkaline media. At the right top of the model, there is a window showing the curve of pH value as a function of added quantity of mono-molar solution of titration acid or base.
It is interesting to follow typical features of this curve depending on solution composition. In case of acid buffer, increase of acid quantity results in shifting stoichiometric point to the right and slightly up, while initial pH value of the solution is shifted down. Adding of salt results in lifting both initial pH value and (slightly) stoichiometric point. It is important that the whole plateau of pH curve is shifted, i.e. changing quantity of salt makes it possible to change in a flexible way stable acidity of the buffer. No horizontal shift of stoichiometric point is caused by addition of salt.
In case of basic buffer, the situation with almost all processes is reverse: addition of alkali results in lifting initial point and makes stoichiometric point lower a little (however horizontal shift of the stoichiometric point is made again to the right). Addition of salt shifts both points down.
Upon pushing "Run" button, titration procedure starts. Titration solution is added to the buffer, current values of added solution amount and pH are shown on the plot. The color of solution depends on both pH value and the type of indicator added to the buffer. As it is known, litmus turns blue with high pH values, while methyl orange turns yellow and phenolphtaleine - pinkish. On the contrary, with low pH values, litmus is red, methyl orange is reddish-orange, and phenol-phtaleine is colorless.
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