The Acid Base Titration

Acid Base Titration is a frequent procedure in the laboratory of volumetric analysis. Useful to determine the concentration of an unknown solution which is under study. The chemical units of concentration “Normality” are used.

What is the degree Acid Base?

In chemistry, the term "degree" is sometimes used to describe the strength or concentration of an acid or a base. However, this usage is not very common or standardized, and it can be ambiguous.

The most common way to describe the strength of an acid or a base is to use its pH value, which is a measure of the concentration of hydrogen ions (H+) or hydroxide ions (OH-) in a solution. A lower pH value indicates a stronger acid, while a higher pH value indicates a stronger base.

Another way to describe the strength of an acid or a base is to use its dissociation constant, which is a measure of how readily the acid or base donates or accepts protons. The dissociation constant is usually represented by the symbol Ka for acids and Kb for bases.

In summary, while the term "degree" can be used to describe the strength or concentration of an acid or a base, it is not a standardized or widely used term in chemistry. pH and dissociation constants are more commonly used to describe the acidity or basicity of a solution.

It is a widely used volumetric and quantitative analysis procedure. In which a solution of known concentration called a titrant. It is added to a solution of unknown concentration called an analyte. From a burette until reaching the equivalence point or end of the degree. It is aimed at determining the unknown density of an acidic solution.

Neutralized by a known base or the other way around. The name volumetric analysis refers to the measurement of the volume of solution employed. It allows to know the degree purity of some substances. It is necessary to use an indicator, a potentiometer, a pH-meter so that a color change, sudden change of potential is observed.

The pH difference when the equivalence point is reached. In this type of method it is preferable to perform the pH measurement while the reaction is proceeding due to the transfer of hydronium ions [ H+] between the acid and the base.   An indicator is like a dye sensitive to pH changes.

They are weak organic acids or bases and their turn is located one pka unit above and one pH unit below

Types of Acid Base titration

Four types of titration are known, acid–base, redox, precipitation, complex formation. Acid-base neutralization Its basis is the neutralization reaction between the ions [H3O+] Y [ OH-], reaching the PH value = 7. When more solution is added it can be acidic or basic. By the pH values given in the reaction a curve can be given.

Redox assessment. In this type of titration, the test solution is allowed to react with a solution that oxidizes or reduces. Electrons are transferred or gain electrons.  The procedure is to add volumetric solution until the test substance reacts. The product is achieved only if the saturation point of the test solution is not passed.

Then it is necessary to know the saturation point. To have the security in the value of measures. This value is located by means of potentiometric indicators. Precipitation reactions combine highly soluble substances with substances that are not well diluted. The result is obtained when the chemical reaction is completed.

The lowering of the substance that was diluted with difficulty is visible. They need long times for because the conditions the rate, quantification and determination of the equivalence point inhibit the precipitation reaction useful. The formation of Complexes is based on the fact that it forms soluble complexes. These are everyday reactions.

Common but do not meet the requirements for use in analytical chemistry. Because they are very unstable. Currently the chelating agents, the di-sodium salt of ethylene-di-amino-tetracetic acid is used as a reagent.(EDTA), who presents one of the greatest developments in analytical chemistry. Almost all metals can be found there.

Titrations Acid Base curve

They are representations of the pH as a function of the amount of solution assessed, added to the analyzed solution. Very useful to determine exactly the equivalence point and to decide which indicator to use so that the final point is clearly appreciated. It is the realization of a graph that is made with the data obtained from the titration.

Between the PH values and the volume values in (ml). The change in the PH values can be observed and then, to the inflection point of the curve. Its volume indicates the amount of titrating substance spent for the analyte to react. They are useful to accurately determine the equivalence point and to decide which indicator you will use to observe more clearly.

The way to behave in the titration of an HCL solution of unknown concentration. Titrated with a 0.1 M solution of NAOH. It is observed that at the ends of the curve the pH variation is smooth. The amount of NAOH added. In the vicinity of the endpoint it is noted that for small amounts of solution titrated.

Indicators of acid base titrations

It is he who gives color to the solution when it reaches the final point, due to the modification of the pH. The turn coincides with the equivalence point. They are usually some acidic and others weak basic. They are classified in auto indicator (analyte-titrant) as the KMnO4. Colored, they are intense, widely used and a few drops are introduced directly into the solution.

It is clearly observed. Fluorescent, it is less change in dissolution. Absorption, the color is observed when they are adsorbed or desorbed by the colloids in the problem solution.Indicators of adsorption. They are substances that change color when adsorbed or desorbed. By the colloids that are formed within the dissolution problem.

As a result of the reaction between the analyte and the titrating substance.  The following are known: Cresol Red, yellow, turn between 0.2 – 1.8. Thymol blue, yellow, turn between 1.8 – 2.8. Congo red, red, turn between 3.0 – 5.2. Methyl orange, yellow- orange, turns between 3.1 – 4.4. Bromocresol blue, green, turning between 3.8 – 5.4.

Bromocresol green, greenish blue, turn between 3.8 – 5.4. Methyl red, yellow, turn between 4.2 - 6.2. Litmus, blue, turning between 5.0 – 8.0. Bomocresol purple, purple, turn between 5,2 - 6,8. Bromothymol blue, blue, turn between 6.0 - 7.6. Neutral red, yellow, turn between 6.8 – 8.4. Cresol red, 2°-, purple, turn between 7.1 - 8.8. Thymol blue 2°, blue, turn between 8.0 - 9.6.

Phenolphthalein, magenta, turn between 8.2 – 10.0.Thymolphthalein, yellow, turn between 9.3 – 10.5. Indigo carmine, yellow, turn between 11.6 – 14.0.

Acid base titrations laboratory practice

The titration process requires the standardization of solutions before being evaluated, that is, the measurement of their concentration experimentally for this, the practice for HCL with NAOH will be addressed. We will start with the practice for acid (HCL), titrant. A solution of the acid (37%, density 1.18 g/ml) is prepared in a volumetric flask.

With water to complete one liter. Who will be valued with Na2CO3, add phenolphthalein and methyl orange. The turn is made when the CO3- is transformed into [HCO3-]. The titrated solution will be introduced into a burette with adequate capacity to add dropwise to the titrated NaOH solution.

Taking into account that the amount of the known compound should be weighed, dissolve in distilled water up to one liter in the volumetric flask.  For standardization of a NaOH solution. Weigh 4 gr and dissolve in distilled water in a volumetric flask up to one liter. Introduce into a burette by applying it little by little to a solution of potassium acid oxalate with phenolphthalein.

Until the equivalence point is reached where the pH to select the indicator for acid-base titration (HCL - NaOH).

1. Preparation of a standard sodium hydroxide (NaOH) solution: To prepare a standard NaOH solution, a known mass of NaOH is dissolved in a specific volume of water to create a solution with a known concentration. The solution is then standardized by titrating it with a known concentration of a standard acid solution, such as hydrochloric acid (HCl), until the endpoint is reached. The concentration of the NaOH solution can then be calculated from the volume and concentration of the HCl solution used.
2. Determination of the acidity of a sample of vinegar: To determine the acidity of a sample of vinegar, a known volume of the vinegar is titrated with a standardized solution of NaOH. An indicator, such as phenolphthalein, is used to signal the endpoint of the titration, which occurs when all of the acetic acid in the vinegar has reacted with the NaOH. The concentration of the acetic acid in the vinegar can then be calculated from the volume and concentration of the NaOH solution used.
3. Determination of the alkalinity of a sample of water: To determine the alkalinity of a sample of water, a known volume of the water is titrated with a standardized solution of HCl until the endpoint is reached. An indicator, such as bromothymol blue, is used to signal the endpoint, which occurs when all of the carbonate and bicarbonate ions in the water have reacted with the HCl. The alkalinity of the water can then be calculated from the volume and concentration of the HCl solution used.
4. Determination of the amount of calcium carbonate in a sample of limestone: To determine the amount of calcium carbonate in a sample of limestone, the sample is first dissolved in a known volume of HCl. The resulting solution is then titrated with a standardized solution of NaOH until the endpoint is reached. The amount of calcium carbonate in the limestone can then be calculated from the volume and concentration of the NaOH solution used.
5. Determination of the buffering capacity of a buffer solution: To determine the buffering capacity of a buffer solution, a known volume of the buffer solution is titrated with a standardized solution of HCl or NaOH while the pH of the solution is monitored. The buffering capacity of the solution can then be determined from the volume and concentration of the acid or base solution required to change the pH of the solution by a specific amount.

Application of Acid Base titrations

Acid-base titration is a widely used analytical technique in chemistry. It involves the gradual addition of a standard solution of a strong acid or base to an unknown solution of an acid or base until the reaction is complete, which is indicated by a change in the pH of the solution. The amount of acid or base in the unknown solution can be calculated from the volume and concentration of the standard solution used.

Here are some common applications of acid-base titrations:

1. Determination of the concentration of an acid or base: Acid-base titration is a common method used to determine the concentration of an acid or a base in a solution. This is important in many fields such as food science, pharmaceuticals, and environmental monitoring.
2. Quality control in the manufacturing of pharmaceuticals and other products: Acid-base titration can be used to monitor the purity and concentration of various chemicals used in the production of pharmaceuticals, cosmetics, and other products.
3. Analysis of water quality: Acid-base titration can be used to analyze the quality of water, including the levels of acidity and alkalinity. This is important in environmental monitoring and for ensuring that water is safe for human consumption.
4. Determination of the equivalence point of an acid-base reaction: The equivalence point is the point at which the number of moles of acid is equal to the number of moles of base in a solution. Acid-base titration can be used to determine the equivalence point of a reaction, which is useful in the study of chemical reactions and in the design of chemical processes.
5. Study of acid-base reactions: Acid-base titration is a common technique used in the laboratory to study the behavior of acids and bases in solution. This is important for understanding the chemistry of many natural and synthetic systems.