Find the exact concentration of an acid solution

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The task set is to find the exact concentration of an acid solution.  It is believed to have a concentration of between 0.05 and 0.15 mol dmˉ³.

Introduction:

Acids dissolve in water with dissociation and the formation of hydrogen ions.  They are classed as strong or weak depending on the extent to which this dissociation occurs.  Bases are substances that liberate hydroxide ions in water.  They too are classed as weak or strong.

The strength of an acid will depend upon its tendency to donate protons.  Similarly, the strength of a base will depend upon its tendency to accept protons: the stronger this tendency, the stronger the acid or base.  An acid with a strong tendency to lose a proton (a “strong acid”) will have a conjugate base with a weak tendency to accept a proton (a “weak base”).  An acid with a weak tendency to lose a proton (a “weak acid”) will have a conjugate base with a strong tendency to accept a proton (a “strong base”).

Titration is ‘a technique used for finding the volume of one solution chemically equivalent to a given volume of another, usually by adding the first solution slowly until equivalence is reached.  This can be detected by the addition of a small amount of an indicator material.’   -   The Cambridge Encyclopaedia

It is this technique that will assist in finding the exact concentration of the acid in this experiment.

Apparatus:                ∙   burette

                           clamp stand

                           pipette

                           conical flask

                           volumetric flask

                           white tile

                           weighing bottle

                           balance

                           funnel

                           distilled water

                           methyl orange indicator

                           sulphuric acid

                           solid anhydrous sodium carbonate

Quantities:

The sulphuric acid supplied is believed to have a concentration of between 0.05 and 0.15 mol dmˉ³, so I plan to make up a sodium carbonate solution with a concentration of 0.1 mol dmˉ³ as this is the mid point.

I believe that 25cm³ of sulphuric acid and 10 drops of indicator will be adequate to gain satisfactory results.  

‘Acids and alkalis are classified as ‘strong’ or ‘weak’ depending on the extent to which they form ions when dissolved in water.’  From the information sheet on the use of indicators in acid/alkali titrations I can see that sulphuric acid is a ‘strong’ acid and sodium carbonate is a ‘weak’ alkali.  The sheet also states which indicator is suitable for titrations between different strength acids and alkalis:

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‘For a titration between a strong acid and a weak alkali, methyl orange is used as the indicator.

For a titration between a weak acid and a strong alkali, phenolphthalein is used as the indicator.

For a titration between a strong acid and a strong alkali, either methyl orange or phenolphthalein can be used as the indicator, although methyl orange is usually chosen.

For a titration between a weak acid and a weak alkali, no indicator is suitable, and a pH meter, conductivity meter or temperature probe has to be used.’

As this titration is between a strong ...

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