JOMO KENYATTA UNIVERSITY
AGRICULTURE AND TECHNOLOGY
DEPT: CIVIL ENGINEERING
UNIT: CHEMISTRY 1 (SCH 2109)
Determination of Concentration of Hydrochloric Acid in a Given Solution
by ARAKA BRAMWEL MBOGO
STANDARDIZATION and DETERMINATION OF THE CONCENTRATION OF HYDROCHLORIC ACID PRESENT IN A GIVEN SOLUTION
To be able to standardize Sodium Hydroxide (NaOH) solution using a standard solution of Oxalic acid. To be able to prepare standard solutions.
To determine the strength of a given solution of Hydrochloric acid (HCl) To analyze errors that occur during standardization experiments.
A standard solution can be defined as a solution that contains a precisely known concentration of a substance. Concentration refers to the abundance of a substance in its mixture or solution. Standard solutions are used to determine the concentration of other substances with which they react in known ratios/proportions. Standardization, therefore, refers the process in which the value of a potential standard is fixed by a measurement made with respect to a standard whose value is known; or simply the act of accurately determining the concentration of a substance by titrating it with a solution of accurately known concentration (standard solution). Standardization, therefore, basically involves titration, especially acid-base titration. Common reagents used for standardization of acids include:
Pure sodium carbonate
Pure borax (sodium metaborate)
Pure calcium carbonate (Iceland spar)
Common reagents used for standardization of alkalis comprise of solid crystalline acids like:
Good standardizing reagents should have the following characteristics:
They should have a high degree of purity
They should be stable and unaffected by the atmosphere, i.e they should not be efflorescent or deliquescent, for easy weighing. They should have a relative molecular mass such that a solution of about 0.01M to 0.5M can be prepared easily.
A standard solution of NaOH cannot be made by direct weighing. This is because NaOH is hygroscopic and will therefore absorb moisture from the air. Therefore, a standard solution of some stable acid (e.g Oxalic acid) has to be prepared to standardize the given Sodium Hydroxide solution. This can then be used to determine the unknown concentration of the Hydrochloric acid solution.
In the experiment, two titrations were therefore performed:
Titration A: Standardization of Sodium Hydroxide solution using standard solution of Oxalic acid. Titration B: Determination of the concentration of Hydrochloric acid solution using the standardized Sodium Hydroxide solution.
The terms used in titration are therefore used here too.
in titration A, the analyte was the Sodium Hydroxide solution; and the titrant was the Oxalic acid.
In titration B, the analyte was the Hydrochloric acid solution; while the titrant was the Sodium hydroxide solution.
Precaution: Oxalic acid is very poisonous.
Oxalic acid (Ethanedioic acid)
Sodium hydroxide solution
Hydrochloric acid solution (of unknown strength)
Titration A: Standardization of NaOH Solution
A standard solution of Oxalic was made by measuring 0.63g of Oxalic acid and adding it to distilled water in a volumetric flask. The mixture is shaken till the crystals dissolve and the solution is made up to 250ml. 25ml of this standard solution is pipetted into a conical flask and two to three drops of the indicator are added to it. The contents of the flask are then titrated against the NaOH solution from the burette till a permanent light pink colour is obtained. The titrations were repeated till concordant results were obtained and then recorded.
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