How To Solve A Titration Problem

How To Solve A Titration Problem-56
The titration curve for the weak acid begins at a higher value (less acidic) and maintains higher p H values up to the equivalence point.This is because acetic acid is a weak acid, which is only partially ionized.

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Figure 2 presents several indicators, their colors, and their color-change intervals.

Titration curves help us pick an indicator that will provide a sharp color change at the equivalence point.

An indicator’s color is the visible result of the ratio of the concentrations of the two species In (a p H of 4.4), most of the indicator is in the yellow ionic form, and a further decrease in the hydronium ion concentration (increase in p H) does not produce a visible color change.

The p H range between 3.1 (red) and 4.4 (yellow) is the color-change interval of methyl orange; the pronounced color change takes place between these p H values.

The p H increases slowly at first, increases rapidly in the middle portion of the curve, and then increases slowly again.

The point of inflection (located at the midpoint of the vertical part of the curve) is the equivalence point for the titration.It indicates when equivalent quantities of acid and base are present.For the titration of a strong acid with a strong base, the equivalence point occurs at a p H of 7.00 and the points on the titration curve can be calculated using solution stoichiometry (Table 4 and Figure 1).The titration of a weak acid with a strong base (or of a weak base with a strong acid) is somewhat more complicated than that just discussed, but it follows the same general principles.Let us consider the titration of 25.0 m L of 0.100 sodium hydroxide and compare the titration curve with that of the strong acid.Solution (a) Assuming that the dissociated amount is small compared to 0.100 H and are both approximately equal to , and their concentrations are the same.Since the amount of the added base is smaller than the original amount of the acid, the equivalence point has not been reached, the solution remains a buffer, and we can use the Henderson-Hasselbalch equation: Note that this result is the same as for the strong acid-strong base titration example provided, since the amount of the strong base added moves the solution past the equivalence point.The p H at the equivalence point is also higher (8.72 rather than 7.00) due to the hydrolysis of acetate, a weak base that raises the p H: H.(b) Find the p H after 25.00 m L of the Na OH solution have been added.The equivalence points of both the titration of the strong acid and of the weak acid are located in the color-change interval of phenolphthalein.We can use it for titrations of either strong acid with strong base or weak acid with strong base.

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