What is the Boehm Back Titration end point?

[Upasna Rai]

Since I used a pH meter to determine the end point, I need to know if this technique is correct:

For the basic solutions, I first titrated with HCl to a pH of 2 and then back titrated with NaOH to a pH of 7. Whereas if I am to use the same procedure for the acidic (HCl) solution must I titrate it with NaOH to a pH of 12 and then back titrate with HCl to a pH of 7?

Please help!

 

[symbolipoint]

The essential idea is that the HCl Titrant undoes what the NaOH titrant does. You intentionally quickly add too much of one titrant, and undo that using the other titrant. You still must measure how much of both titrants (each titrant) that you used. The idea is to be able to complete the titration faster.

NOTE: Unsure if this post should be deleted or not. I found very little about Boehm method of titration in a websearch, but the back-titration is part of the method, as I infer. Initial excess titrant is part of a sample treatment process.

 

[epenguin]

Titrated what?

 

[Upasna Rai]

Could you explain how the chemistry works. From the point that the carbon is made to react with the base to the point that it is titrated with a base to determine acidic functional groups?

 

[Upasna Rai]

The four Reactant (R) solutions used to carry out Boehm Titrations were 0.05 M solutions of Sodium Hydroxide (NaOHR), Sodium Carbonate (Na2CO3R), Sodium Bicarbonate (NaHCO3R) and Hydrochloric Acid (HClR). Of the four, Sodium Hydroxide and Hydrochloric Acid were also used as Titrant (T) solutions, denoted by (NaOHT) and (HClT) respectively. Prepared solutions were subjected to Nitrogen (N2) gas purging for two hours.

Each batch of carbon sample preparation and testing was divided into 2 parts. While one was acidic (HClR) used to test for basic oxygen functional groups using direct titration, the other was basic (NaOHR, Na2CO3R and NaHCO3R) used to test for acidic oxygen functional groups using back titration. Each carbon sample was run in duplicates along with its corresponding blank (no carbon) sample.

The carbon sample contents were 25 mL of Reactant (R) solution and 0.5 g of dried carbon. Once prepared and sealed, the carbon samples were subjected to rotation for 72 hours. The samples were then filtered using a 45 μm Whatman filter paper and 20 mL of filtrate was retained for titrations.

Once prepared and sealed, the acidic samples were purged with N2 gas and directly titrated against NaOHT to a pH of around 7 and the volume of NaOHT was noted. The basic samples were first purged with N2 gas and titrated against HClT till the pH reached around 2 and then back titrated with NaOHT to a pH of around 7.

 

[PrasadPore]

@Upasna Rai:0 Can you please help me with the formula for finding the amount of Carboxylic, Lactonic, Phenolic and Surface Acidic Groups; if we consider the neutralization assumptions?