Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

This simple calculation indicates clearly that the dominating form is HIn which is why the solution we

appear as red.

A relevant question is thereby how much of In- that have to be in the solution in respect to HIn in order for

the human eye to be able to detect the two colours. For the most indicators it is a rule of thumb that at least

one tenth of HIn must be changed into In- before the human eye may be able to detect the change in colour.

5.7 Summing up on chapter 5

In this fifth chapter we have looked at central part of the aqueous chemistry being acid/base chemistry. We

initially saw how a H+ ion from the acid to the base is transferred and how acid strength is defined

analogously to the principles of equilibrium we say earlier in chapter 4. further the pH scale was defined and

we saw how water molecules may be able to react with itself in the process of autoprotolysis. The

autoprotolysis of water contributes to the H 3 O+ and OH- concentration but may in most cases be neglected

unless the calculated values of H 3 O+ and OH- concentrations are in the order of 10-6 M or less.

Calculations of pH in different types of solutions was exemplified including calculations of pH values I

strong and weak acid solutions. As an example of an advanced pH calculation we saw how pH values may

be calculated in a solution containing two weak acids. It was clear from these examples how closely pH

calculations are connected to the equilibrium conditions in the given solution.

We saw in the following section how polyprotic acids are capable of providing more H+ ions in several steps

and we saw how pH ay be calculated in solutions of polyprotic acids. In connection with this we looked

briefly at acid and base properties of salt and on how pH may be calculated in such salt solutions. In

connection with the influence of foreign ions on the equilibrium conditions in chapter 4 we looked briefly at

ion effects and its influence on pH conditions.

Further we introduced buffer chemistry and saw how pH may be calculated in buffer solutions and on how

the buffer equation is often used in practice. When one has a solution of a weak acid and its corresponding

weak base, both in concentrations of the same magnitude, one has a buffer system and the buffer equation

may be used to calculate pH. Lastly, we looked at titration and on pH curves exemplifyed through examples

of titration of monovalent weak acid with strong base and titration of divalent acid likewise with strong base

NaOH. In the end we saw how colour indicator work.

Acids and bases