Quantitative Chemistry –Titration
Determination of the Molarity of an Unknown Solution through Acid-Base Titration Technique
The aim of this investigation was to determine the precise molarity of two (NaOH(aq)) sodium hydroxide solutions produced at the beginning of the experiment through the acid-base titration technique. 1.2 Theoretical Background
Titration is a method commonly used in laboratory investigations to carry out chemical analysis. The most frequent chemical analysis performed through titration is when determining the exact concentration of a solution of unknown molarity. This technique is usually used in redox and acid-base reactions. Redox reaction is when reduction – lost of oxygen – of one of the substances present in a reaction occurs and subsequently oxidation – gain of oxygen – of the second substance in the same reaction takes place. On the other hand, acid-base reaction is when a solution of known molarity2 and volume present in a conical flask is titrated against a solution of unknown molarity in a burette until neutralization is reached. As I have shown in eq.1, in this investigation it was an acid reacting with a base, hence, an acid-base titration. eq.1 – Hydrochloric Acid + Sodium hydroxide Sodium Chloride + water HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) In this investigation the latter reaction was carried out, having hydrochloric acid (HCl(aq)) as the analyte in the conical flask and sodium hydroxide (NaOH(aq)) as the titrant in the burette. The analyte was also designated as the standard solution of the experiment, since it has known values of volume and concentration, the figures that allowed the molarity of the titrant to be calculated. In an acid-base titration, the titrant in the burette is gradually added to the analyte in the conical flask until neutralisation happens, thus, the reaction reaches completion. When neutralisation happens the substances present at the end point are stoichiometrically equivalent, in other words, the value of moles of NaOH(aq) present at the end of the reaction is equivalent to the value of moles of HCl(aq) in the same solution as shown on eq.2 below. eq.2 – HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) 1 : 1
The end point of a titration reaction can be obtained through two major methods. Firstly is by using a pH meter which works by introducing electrodes to the flask containing the standard solution. Once in the conical flask, these electrodes would measure the H+ ions present in the conical flask since they change as the titrant in added, until neutralisation happens, as a result, determining the pH of the solution. Knowing that neutralization happens when the pH of the solution is equal to 7, consequently, at the end point the pH meter will read 7. The second method would be using a colour indicator this could be paper or in liquid form. In an acid-base titration it would be convenient to use an indicator in liquid. For instance, phenolphthalein is a recurrent indicator in this type of reaction which is colourless in an acidic solution and turns pink when in a basic solution. This indicator works by adding a few drops into the conical flask containing the acidic analyte and titrate the basic titrant drop-wise until colour of the solution formed in the conical flask changes to pink. All things considered, the colour indicator was used in this experiment since it is the most accessible method to measure the end point of an acid-base titration. The purpose of this investigation was to determine the unknown molarity of NaOH(aq) from acid-base titration. The preparation of NaOH(aq) was done by the students performing this investigation. The students were allocated mass of NaOH(s) that was diluted in water and...
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