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The indicator base

The differently coloured indicator acid and the indicator base are in a chemical equilibrium. In a basic environment, the indicator acid IndH gives off a proton - pay someone to do my online class . This creates the negatively charged ion of the indicator and determines the colour of the solution. In the acidic pH range, the proton is taken up again and the solution shows the colour determined by the indicator acid.

The colour change is not sudden, but depends on the concentration ratio c(HInd)/c(Ind-) of indicator acid and indicator base in a certain pH range, the transition range. The turnover ranges comprise approx. 2 pH value units. An envelope of about 2 pH-value units results from the fact that the eye, for example, can only clearly recognise the colour red of the indicator methyl red at a concentration ratio of indicator acid - chemistry solver : indicator base of about 10 : 1 and, correspondingly, the colour yellow is only clear at a ratio of acid : base of about 1 : 10. The difference between the two limits corresponds to a factor of 100.

An example is 1,4-nitrophenol or para-nitrophenol, which changes from colourless (acidic) to deep yellow (basic) in the neutral range:

Another example is methyl red . This dye, which belongs to the group of azo dyes, changes from red to yellow - do my homework . However, this change does not take place in the neutral range, but in the range of pH 4.2 to 6.3. It is often added to acidic decalcifiers (= substances that free appliances or machines from deposited lime in the water) to indicate when the acid that dissolves the lime has been used up.

Since the reaction is dependent on the strength of the indicator acid or base, different turnover ranges exist and the indicators can be used for different pH ranges.

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