An acid is a solution which has a high concentration of hydrogen positive ions (H+) while an alkali (base) is a solution with high levels of hydroxide ions (OH-), when combined the result is H2O (water) and a salt. The acidity of acids and alkali solutions can be determined and the strength measured on a 0-14 scale, measured through pH indicators. When opposite pH solutions combine, a neutral pH of 7 forms with the production of salt and water. The pH scale is a reciprocal of a logarithmic scale for measuring the concentration of H+ ions in each mole per litre, such that pH 7 (neutral) is written as 10-7mol L-1. Hence every integer increase on a pH scale the amount of H+ ions per litre decreases by a factor of ten, becoming more alkali.
A pH indicator is a weak acid or alkali, when placed in water the molecules disassociate slightly and form ions. A universal indicator is a mixture of many indicators providing different colours for each level of pH. This allows a more accurate indication of the solution PH then that which only provides two different colours, for instant Phenolphthalein. Some wavelengths of visible light can be absorbed by double and single bounds from the Phenolphthalein indicator, giving the solution a colour. Due to the large concentration of H+ ions in an acidic solution, when the universal indicator is introduced the molecules attach to the H+ resulting in an abundance of single bonds absorbing the same wavelength and producing a defined colour. However, when introduced into an alkali solution the distinct lack of H+ ions result in the more double bonds forming, changing the wavelength of light that is absorbed so that the solution appears another colour.
Used in analytical chemistry, the method of titration is employed to determine the concentration or amount of a substance through its reaction with another substance of know concentration and volume. In this process the known reagent, the titrant, is accurately measured and carefully dripped into a flask containing the other reagent of opposite concentration. A PH indicator is put into the second reagent, so that as the titrant is added and a chemical stoichiometric reaction occurs, the point of equilibrium (PH 7) can be determined with ease. From the known concentration of the titrant and the volume required to equalise the unknow reagent, a stoichiometric calculation can be implemented to discover the missing variable of the second reagent’s concentration.
The purpose of this investigation is to utilize a stoichiometric relationship between sodium carbonate, Na2CO3, and hydrochloric acid, HCl, to ultimately determine the concentration of an unknown solution of HCl.
If an amount of hydrochloric acid is titrated into an aqueous solution of sodium carbonate, then a natural solution will form that will allow us to determine the concentration of hydrochloric acid because of the stochiometric relationship between the two...