Question

I found difficulty to differentiate the blank titration and back titration problems/Questions. Can anyone give me the problems/questions of these two titrations..?? (and please give the explanation between these titrations, so i can understand). Thank you so much :)

Answer 1

A blank titration is done without the analyte present to check for possible sources of error in the "blank" solution. For example, de-ionized water is slightly acidic and may affect the results of an acid base titration (if you want a highly accurate concentration). So you would do a blank titration to find the concentration of H3O+ in the water by titrating standard basic solution and use it to correct the concentration of your analyte.  

A back titration is used when it is difficult to find an endpoint in a normal titration (for example, if the analyte is not very soluble in water). You react the analyte with an excess of titrant and then titrtate the excess titrant. Subtraction of the moles of excess titrant from the original amount you used gives the moles of titrant reacted with the analyte. From that you can figure out moles of analyte. In a back-titration, excess amount of the standard titrant is added to the analyte. Then some amount of the standard titrant will react with the analyte and the excess of it can be determined by a back-titration. For example, the amount of phosphate in a sample can be determined by this method. When excess amount of silver nitrate is added to a phosphate sample, both will react to give silver phosphate solid. Then the excess of silver nitrate is titrated with potassium thiocyanate. Therefore, the total amount of added silver nitrate is equal to the amount of phosphate ion and the amount of thiocyanate used for the back-titration.