There are several characteristics that are seen in all titration curves of a weak acid with a strong base. These characteristics are stated below. The image of a titration curve of a weak acid with a strong base is seen below.
All of the characteristics described above can be seen within it. When solving a titration problem with a weak acid and a strong base there are certain values that you want to attain.
These include the initial pH, the pH after adding a small amount of base, the pH at the half-neutralization, the pH at the equivalence point, and finally the pH after adding excess base. This data will give sufficient information about the titration. Below is an example of this process. Find the pH at each of the following points in the titration of 25 mL of 0. The question gives us the concentration of the HF. However, this only gives us the millimoles. To get the concentration we must divide by the total volume.
Since an acid and its conjugate base are in equilibrium we can attempt to use the Henderson-hasselbalch equation. However, for this to work the reaction must follow certain rules.
The ratio of the conjugate base and weak acid must be between 0. Also, both the ratio of the conjugate base and k a value and the ratio of the acid and k a value must exceed This is between 0. These both exceed one hundred. Therefore, we continue by using the Henderson-hasselbalch equation.
The millimoles of OH - added in To find the concentrations we must divide by the total volume. After the equivalence point it is like the end of the ethanoic acid - NaOH curve. Notice that there isn't any steep bit on this graph. Instead, there is just what is known as a "point of inflexion". That lack of a steep bit means that it is difficult to do a titration of a weak acid against a weak base.
Note: Because you almost never do titrations with this combination, there is no real point in giving the graph where they are added the other way round. It isn't difficult to work out what it might look like if you are interested - take the beginning of the sodium hydroxide added to ethanoic acid curve, and the end of the ammonia added to hydrochloric acid one.
The reason that it is difficult to do these titrations is discussed on the page about indicators. The way you normally carry out a titration involves adding the acid to the alkali.
Here are reduced versions of the graphs described above so that you can see them all together. The overall equation for the reaction between sodium carbonate solution and dilute hydrochloric acid is:. If you had the two solutions of the same concentration, you would have to use twice the volume of hydrochloric acid to reach the equivalence point - because of the 1 : 2 ratio in the equation. Suppose you start with 25 cm 3 of sodium carbonate solution, and that both solutions have the same concentration of 1 mol dm That means that you would expect the steep drop in the titration curve to come after you had added 50 cm 3 of acid.
The graph is more complicated than you might think - and curious things happen during the titration. You expect carbonates to produce carbon dioxide when you add acids to them, but in the early stages of this titration, no carbon dioxide is given off at all. Then - as soon as you get past the half-way point in the titration - lots of carbon dioxide is suddenly released.
The graph is showing two end points - one at a pH of 8. The reaction is obviously happening in two distinct parts. In the first part, complete at A in the diagram, the sodium carbonate is reacting with the acid to produce sodium hydrogencarbonate:.
In the second part, the sodium hydrogencarbonate produced goes on to react with more acid - giving off lots of CO 2. It is possible to pick up both of these end points by careful choice of indicator. That is explained on the separate page on indicators. Ethanedioic acid was previously known as oxalic acid. It is a diprotic acid , which means that it can give away 2 protons hydrogen ions to a base.
Something which can only give away one like HCl is known as a monoprotic acid. The reaction with sodium hydroxide takes place in two stages because one of the hydrogens is easier to remove than the other. The two successive reactions are:. If you run sodium hydroxide solution into ethanedioic acid solution, the pH curve shows the end points for both of these reactions. The curve is for the reaction between sodium hydroxide and ethanedioic acid solutions of equal concentrations. If this is the first set of questions you have done, please read the introductory page before you start.
The equivalence point of a titration Sorting out some confusing terms When you carry out a simple acid-base titration, you use an indicator to tell you when you have the acid and alkali mixed in exactly the right proportions to "neutralise" each other.
But that isn't necessarily true of all the salts you might get formed. To summarise: The term "neutral point" is best avoided. Simple pH curves All the following titration curves are based on both acid and alkali having a concentration of 1 mol dm Titration curves for strong acid v strong base We'll take hydrochloric acid and sodium hydroxide as typical of a strong acid and a strong base.
At this point we have all we need to calculated the charge. This suggests a bisecting root finder as a path to a solution and that works very well. Many are going to shift the waters charge balance. Sign up to join this community.
The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Shouldn't the pH at the equivalence point always be 7? Ask Question. Asked 7 years, 9 months ago. Active 3 years, 9 months ago. Viewed 63k times. My question: If I add 1 mole of ethanoic acid to 1 mole of sodium hydroxide, I should get a neutral solution and the pH should be 7.
Improve this question. Eliza Eliza 2, 8 8 gold badges 27 27 silver badges 42 42 bronze badges. Acetate is the conjugated base of a weak acid and is therefore strong enough to significantly alter the pH: that's why the final pH is 9. The former would be the same as referring to the mass as " number of kilograms". Add a comment. Active Oldest Votes. Improve this answer.
Also, in the case of strong acid and weak base, will a weak conjugated acid form? Show 2 more comments.
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