![]() 4, then the Phenolphthalein indicator would be used instead of Alizarin Yellow because phenolphthalein would reduce the indicator error. Thus, a careful selection of the indicator will reduce the indicator error.įor example, if the equivalence point is at a pH of 8. The endpoint and the equivalence point are not exactly the same because the equivalence point is determined by the stoichiometry of the reaction while the endpoint is just the colour change from the indicator. The acid-base indicator indicates the endpoint of the titration by changing colour. In addition to the sample, an appropriate indicator is added to the titration chamber, reflecting the pH range of the equivalence point. 5, then a Thymol Blue indicator may be used.Īcid-base titrations depend on the neutralization between an acid and a base when mixed in solution. On the other hand, if the acid is off the scale, i. , then an Alizarine yellow indicator may be used. Acid–base titration is performed with a phenolphthalein indicator, when it is a strong acid – strong base titration, a bromthymol blue indicator in weak acid – weak base reactions, and a methyl orange indicator for strong acid – weak base reactions. This is best achieved by washing a hanging drop from the tip of the burette into the flask right at the end of the titration to achieve a drop that is smaller in volume than what can usually be achieved by just dripping solution off the burette. The end point is reached when the indicator just changes color permanently. Subtracting the initial volume from the final volume will yield the amount of titrant used to reach the endpoint. The initial and final readings on the burette (prior to starting the titration and at the end point, respectively) should be recorded. ![]() At least three more titrations should be performed, this time more accurately, taking into account roughly where the end point will occur. This is the first (or rough) titre and should be discluded from any calculations. The solution should be let out of the burette until the indicator changes colour and the value on the burette should be recorded. At this stage we want a rough estimate of the amount of this solution it took to neutralize the unknown solution. The known solution should then be allowed out of the burette, into the conical flask. Secondly, a known volume of the unknown concentration solution should be taken with the pipette and placed into the conical flask, along with a small amount of the indicator chosen. First, the burette should be rinsed with the standard solution, the pipette with the unknown solution, and the conical flask with distilled water. A suitable indicator should be chosen, preferably one that will experience a change in colour (an end point) close to the equivalence point of the reaction. The point at which the indicator changes colour is called the end point. However, weak acids are not often titrated against weak bases because the colour change shown with the indicator is often quick, and therefore very difficult for the observer to see the change of colour. If both are of equal strength, then the equivalence pH will be neutral. ![]() When a weak acid reacts with a weak base, the equivalence point solution will be basic if the base is stronger and acidic if the acid is stronger. Acid–base titrations can also be used to find percent purity of chemicals. ![]() It makes use of the neutralization reaction that occurs between acids and bases and the knowledge of how acids and bases will react if their formulas are known. This allows for quantitative analysis of the concentration of an unknown acid or base solution.
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