Results from three separate single endpoint titrations are used to calculate the results. The mixture of H2SO4, HF, and NH4F/HF contains H+ from H2SO4, HF, and NH4F/HF, SO42- from H2SO4, and F- from HF and NH4F/HF. Analysis of total H+ («total acids») by NaOH titration, F- by titrating with Al(NO3)3 («total fluoride») and SO42- by titrating with BaCl2 provides the information required to determine the composition of the mixture.

Sulfate is precipitated by reaction with an acidified barium chromate solution. The excess barium chromate is precipitated by basification with ammonia solution. Residual soluble chromate equivalent to the sulfate content of the sample is titrated with a solution of standard ferrous ion to a thermometrically determined endpoint.

Sulfate is precipitated as barium sulfate by reaction with an acidified barium chromate solution. The excess barium chromate is precipitated by basification with ammonia solution. Residual soluble chromate, equivalent to the sulfate content of the sample, is titrated with a solution of standard ferrous ion to a thermometrically determined endpoint.

Samples of shredded, grated, or sliced cheese are dispersed with a high-speed disintegrator in a solution of trichloroacetic acid, which denatures protein and assists in the liberation of all sodium from the matrix. Toluene is added in a second step of the dispersion process to assist in the solubilization of fat. Ammonium fluoride solution is then added, and the sodium titrated with a titrant comprising 0.5 mol/L Al(NO3)3 and 1.1 mol/L KNO3 to an exothermic endpoint.Na+ + 2K+ + Al3+ + 6F- ↔ NaK2AlF6 ↓In this determination, ammonium fluoride (NH4F) has been found to give sharper endpoints than ammonium bifluoride (NH4F ∙HF). In addition to this application note, you can find more information on thermometric sodium determination in foods in our application video available on YouTube:https://youtu.be/lnCp9jBxoEs

Two separate titration sequences are required to analyze the mixture:- titration of the HF content with Al(NO3)3 (the «elpasolite» reaction)- titration of the H2SO4 with BaCl2 followed by titration with NaOH to determine the «total acids» contentThe HF, H2SO4, and «total acids» contents are converted to a HNO3 equivalent, with the HNO3 content found by subtracting the HF and H2SO4 from the «total acids» content.

A direct thermometric titration (TET) with 2 mol/L NaOH is used to determine the HF, NH4F, and maleic acid (C4H4O4) contents of acid cleaning solutions. Three endpoints (EPs) are obtained, which may be assigned as follows:EP1: C4H4O4 (pKa1 = 1.9), HF (pKa = 3.17)EP2: C4H4O4 (pKa2 = 6.07)EP2: NH4F (pKa = 8.2)The HF content is determined by subtracting the difference (EP2-EP1) from EP1.

This Application Note supplements AN-H-003 with the treatment of the standard addition of sulfate as sulfuric acid. This technique may be contemplated when either sulfate levels are too low for a satisfactory direct titration, or when the sample matrix hinders endpoint detection, leading to poor precision and accuracy.

This Application Note describes the determination of the free and total hydroxide and aluminum oxide content in Bayer process and other aluminate liquors. The method is not subject to interference by carbonate ions. An aliquot of sodium aluminate liquor is titrated with potassium hydrogen carbonate solution to yield the free hydroxide ion content of the liquor.

The presence of the hydrated ion [Fe(H2O)6]3+ can interfere with the determination of «free acid» due to the low pKa value (~2.2) of this ion. Ions of metals such as Fe, Cu, and Al can be masked effectively with fluoride, and permit the determination of the acid content by thermometric alkalimetric titration with good accuracy and precision.

This Application Note deals with the determination of ferric ion in acidic and copper-free solutions using thermometric titration. The ferric ion is reduced by iodide. The released iodine reacts exothermically when titrated with thiosulfate solution. The endpoint is determined through temperature plotting by the temperature sensor Thermoprobe.