This is the practical section of Chemistry. This topic is very fundamental for anyone who would love to study Chemistry as a discipline in a tertiary institution. Volumetric analysis involves measuring the volume of solutions of reactants in chemical reactions, however, weighing is involved, if a reactant is a solid.
Many types of chemical reactions involve volumetric analysis however, only those in respect of neutralization, precipitation, displacement, and redox reactions would be covered on this page. You might be wondering what the aim of Volumetric analysis is and we would love to tell you that the aim is to quantitatively determine the amounts of the reactants used in a chemical reaction, and hence establish the stoichiometry (mole ratio) in order to obtain a balanced equation for the reaction.
Types Of Solutions & Preparation Methods
An aqueous solution is obtained when a solid, liquid, or gas forms a homogeneous mixture with water. Examples of some solutions are outlined below:
Standard Solution: A standard solution is a solution of known concentration. Its concentration can be expressed in grams per dm3(mass concentration) or in moles per dm3(molar concentration). The mathematical relationship between mass concentration and molar concentration of a solution of a chemical substance is Mass concentration = molar concentration * molar mass. A standard solution is prepared by the use of a p[primary standard.
A primary standard is a substance that can be obtained in a high state of purity. It is anhydrous, non-deliquescent, non-hygroscopic, and soluble in water. Examples of primary standards include Anhydrous sodium trioxocarbonate, benzenecarboxylic(bezoic acid), potassium hydrogenphthalate, and ethanedioc acid dihydrate.
Standard solutions can be prepared via the following ways:
- Weighing Method
- Dilution Method: Dilution method is used in obtaining a solution of low concentration from a solution of high concentration. When a known volume (V1) of a standard solution of concentration C1(initial) is diluted with water, its volume increases to V2(final), while its concentration decreases to C2(final). However, the amount n, of the solute before and after dilution remains constant.
Before dilution: Amount, n1 = C1(moldm-3) * V1(dm3)
n1 = C1 * V1
After dilution: Amount, n2 = C2(moldm-3) * V2(dm3)
n2 = C2 * V2
n1 =n2 = C1 V1 = C2 V2
Acid-Base Titrations
Neutralization is the reaction between an acid and a base to produce salt and water only. It is essentially the reaction between H+ from the acid, and OH– from the base, to form water.
H+(aq) + OH–(aq) → H2O(l)
Titration is used to determine the average volume of the acid required to neutralize completely a known volume of the base. In an acid-base titration, the solution of the acid is gradually added into the solution of a base, in the presence of a suitable indicator, until the reaction is complete as signaled by a sudden change in the color of the indicator. This is the endpoint, neutralization point, or equivalence point of the reaction.
At the endpoint, the amounts, in moles of the acid, used and the base taken, are exactly in the same ratio as that required in the balanced equation of the reaction. This is the fundamental basis of all titrations. That is:
The relevant variables in acid-base titrations are:
Ca = Concentration of acid, in moldm-3
Va = Volume of acid used, in cm3(or dm3)
Cb = Concentration of base, in moldm-3
Va = Volume of base used, in cm3(or dm3)
na = Amount of the acid: its coefficient in the balanced equation reaction
na = Amount of the base: its coefficient in the balanced equation reaction
Since both the acid and base are the reactants in the same reaction, then:
Acid Base Titration Apparatus
During acid-base titrations there are some apparatuses are used that are very important. The two most important pieces of apparatus used are burette and pipette. Others are a conical flask, retort stamp with clamp, filter funnel, and white tile.
Acid-Base Indicators
Indicators are mixtures of weak organic acids and bases that change colour depending on the hydrogen ion concentrations, PH, of the solutions. They are used in acid-base titrations to detect the endpoints of the reactions or to test for the acidity or alkalinity of a solution.
| Indicator | In Alkali | In Acid | At Endpoint |
| Litmus Solution | Blue | Red | Purple |
| Methyl Orange | Yellow | Pink | Orange |
| Methyl Red | Yellow | Pink | Red |
| Phenolphthalein | Pink | Colourless | Colourless |
A solution of an acid of unknown concentration can be standardized ie. its concentration determined, by the use of a standard solution of a base, and vice versa.