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Calculation vs Approximation
There are calculations that in many instances are not particularly difficult and which can be attributed to the approximations that are able to be carried out. By using a scientific calculator pH calculations can be processed, but your calculator must be capable of dealing with exponential numbers, logs and inverse logs. In addition, it must have a key facility that changes the sign of the number entered!
In some instances, although not known to what degree, it is debatable as to how good these approximations are, or how reliable the pH value is that has been calculated by using them. Prior to a pH calculator, the lack of a reasonable method utilizing pH calculations, as in the case of acid with similar "Ka" values, gave rise to frustration. This was to transmit itself and stimulate the origination of the first pH calculator!
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For over twenty years, pH calculators were used for the solution of pH related questions from various text books and very often, assisted in discovering errors! This was generally in relation to analytical practice, or for preparation in respect of pH questions for examinations. They were also utilized as helpful tools in electrochemical research. In lectures relating to analytical chemistry, pH calculators were used for the preparation of acid/base titration curves.
With regard to Acids, Bases and pH; there are several means in defining them. However, pH refers only to hydrogen ion concentration and this only has meaning when applied to water based (aqueous) solutions. It must be remembered that when using pH calculations that model of calculator is different in some way.
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The Litmus Test
The Universal Indicator, generally known as a “Litmus Test", together with Hydrion papers, are combinations of different indicators. Several smooth colour changes are produced in respect of a wide range of pH values.The first Litmus was probably used by the Spanish Alchemist, Arnaldus de Villa Nova in about 1300AD. In the sixteenth century and particularly in the Netherlands, the blue dye was extracted from particular lichens.
Wet Litmus paper can be utilised in the testing of water soluble gases; whereby the gas dissolves in the water and the solution from this, gives the paper a blue colour. However, the primary function of Litmus, is the ability to test if a solution is acidic or alkaline? Colour changes to Litmus paper can also be caused by Chlorine gas, which turns a blue litmus paper to white. This particular action is not reversible and in this circumstance, the Litmus is not performing as an indicator.
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Due to the nature of chemistry, any aspect will include the knowledge of pH calculations. In a varied and technical subject like chemistry, any student is advised to research the topic thoroughly and the distance learning facilities available. Costs will naturally depend upon the nature and content of the course selected. In “General Chemistry Online"; there is a well organized and large amount of materials, notes and guides available for students and teachers of introductory college chemistry.
Also to be found there are skills checklists, online self-grading examinations and a question and answer column. It makes for a well designed, comprehensive, interactive guide and web resource.
Oxford University, offer an award winning Virtual Chemistry Laboratory, which was designed and built by Oxford students. It is an ideal online learning media resource for chemistry.
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References and Image Credits