How do you use titration calculations to find pH? What is a redox titration and what is it used for? Why is titration used when standardizing a solution?
Is titration suitable for sodium nitrate? How can I do redox titration calculations? How can I calculate the titration of a weak acid and a strong base? How can I make back titration calculations? Asked 6 years, 6 months ago. Active 3 months ago. Viewed 43k times. I had this question while reading a Chemguide article, on this topic: I think my confusion is caused by the way I look at pKa of acid-base indicator.
Improve this question. Add a comment. Active Oldest Votes. Vocabulary : SB : Strong Base. Improve this answer. I understand what you said is correct, for other situations, but isn't exactly what I am looking for. Show 4 more comments.
Consider titrating an acid with NaOH. MaxW MaxW Karsten Theis Karsten Theis It is also very poorly written. Please use proper syntax and avoid non-standard abbreviations like 'n' for 'and'. Sign up or log in Sign up using Google. Sign up using Facebook. It is important to be aware that an indicator does not change color abruptly at a particular pH value; instead, it actually undergoes a pH titration just like any other acid or base.
Thus most indicators change color over a pH range of about two pH units. We have stated that a good indicator should have a pKin value that is close to the expected pH at the equivalence point. For a strong acid—strong base titration, the choice of the indicator is not especially critical due to the very large change in pH that occurs around the equivalence point.
This figure shows plots of pH versus volume of base added for the titration of The horizontal bars indicate the pH ranges over which both indicators change color cross the HCl titration curve, where it is almost vertical. In contrast, the titration of acetic acid will give very different results depending on whether methyl red or phenolphthalein is used as the indicator.
Although the pH range over which phenolphthalein changes color is slightly greater than the pH at the equivalence point of the strong acid titration, the error will be negligible due to the slope of this portion of the titration curve. In contrast, methyl red begins to change from red to yellow around pH 5, which is near the midpoint of the acetic acid titration, not the equivalence point. The graph shows the results obtained using two indicators methyl red and phenolphthalein for the titration of 0.
Due to the steepness of the titration curve of a strong acid around the equivalence point, either indicator will rapidly change color at the equivalence point for the titration of the strong acid. In contrast, the pKin for methyl red 5. In general, for titrations of strong acids with strong bases and vice versa , any indicator with a pKin between about 4. For the titration of a weak acid, however, the pH at the equivalence point is greater than 7.
Conversely, for the titration of a weak base, where the pH at the equivalence point is less than 7. The existence of many different indicators with different colors and pKin values also provides a convenient way to estimate the pH of a solution without using an expensive electronic pH meter and a fragile pH electrode. Plots of acid—base titrations generate titration curves that can be used to calculate the pH, the pOH, the pKa, and the pKb of the system. The shape of a titration curve, a plot of pH versus the amount of acid or base added, provides important information about what is occurring in solution during a titration.
The shapes of titration curves for weak acids and bases depend dramatically on the identity of the compound. The equivalence point of an acid—base titration is the point at which exactly enough acid or base has been added to react completely with the other component.
The equivalence point in the titration of a strong acid or a strong base occurs at pH 7. In titrations of weak acids or weak bases, however, the pH at the equivalence point is greater or less than 7.
The pH tends to change more slowly before the equivalence point is reached in titrations of weak acids and weak bases than in titrations of strong acids and strong bases. The pH at the midpoint, the point halfway on the titration curve to the equivalence point, is equal to the pKa of the weak acid or the pKb of the weak base. Thus titration methods can be used to determine both the concentration and the pKa or the pKb of a weak acid or a weak base.
Acid—base indicators are compounds that change color at a particular pH. They are typically weak acids or bases whose changes in color correspond to deprotonation or protonation of the indicator itself. Learning Objectives To calculate the pH at any point in an acid—base titration. If one species is in excess, calculate the amount that remains after the neutralization reaction. Determine the final volume of the solution. Calculate the concentration of the species in excess and convert this value to pH.
Solution A Because 0. Answer Titrations of Weak Acids and Bases In contrast to strong acids and bases, the shape of the titration curve for a weak acid or a weak base depends dramatically on the identity of the acid or the base and the corresponding Ka or Kb.
The corresponding curve for the titration of Given: volume and molarity of base and acid Asked for : pH Strategy: Write the balanced chemical equation for the reaction. Determine which species, if either, is present in excess. Tabulate the results showing initial numbers, changes, and final numbers of millimoles. Use a tabular format to obtain the concentrations of all the species present. Answer 9. Unlike strong acids or bases, the shape of the titration curve for a weak acid or base depends on the pKa or pKb of the weak acid or base being titrated.
The shapes of the two sets of curves are essentially identical, but one is flipped vertically in relation to the other. Titrations of Polyprotic Acids or Bases When a strong base is added to a solution of a polyprotic acid, the neutralization reaction occurs in stages. The curve for the titration of Given : volume and concentration of acid and base Asked for : pH Strategy : Calculate the initial millimoles of the acid and the base.
Use a tabular format to determine the amounts of all the species in solution. Calculate the concentrations of all the species in the final solution.
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