Search: titrimetric

The sodium hydroxide bound as aluminate and titrated in the p-value determination is calculated by subsequent determination of the aluminum and deducted, as it is no longer available for purification.

The aluminum determination itself is based on the reaction between aluminum hydroxide and sodium fluoride, in which sodium hydroxide is released and thus serves as a measure for calculating the aluminum.

Carbonates interfering with the titration are precipitated with Ba²⁺ ions.

The aliquot of an extract of malt is added to a buffered starch solution and allowed to stand for exactly 30 min at 20 °C. Then, the maltose – formed primarily from the starch through the action of the β-amylase – is measured using iodine and is determined according to the following chemical reaction:

The analysis involves a reaction with N,N-diethyl-1,4-phenylenediamine (DPD), which forms a compound possessing a red color at a pH of 6.2–6.5. The solution is titrated with an ammonium iron(II) sulfate standard solution until the red color disappears. Total chlorine is measured through the addition of potassium iodide, of which a known amount in excess of that required is added to the solution in advance.

The analysis involves a reaction with N,N-diethyl-1,4-phenylenediamine (DPD), which forms a compound possessing a red color at a pH of 6.2–6.5. In this reaction, chlorine dioxide is reduced to a single chlorite ion. The solution is titrated with an ammonium iron(II) sulfate solution until the red color disappears. The chlorine dioxide concentration in the water sample is calculated on the basis of the quantity of ammonium iron(II) sulfate solution consumed in the titration. The formation of the red color due to the addition of DPD can take place in the presence of other compounds other than chlorine dioxide. The oxidation reaction can be brought about by any oxidizing agent and is dependent upon the redox potential and the concentration of the solution.

Determination of the quicklime (CaO) or sodium hydroxide (NaOH) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding equivalent concentration (normality) up to the color change of phenolphthalein (pH 8.2).

Quicklime

Sodium hydroxide

If the alkaline solution is likely to be strongly influenced by carbonic acid or if the cleaning solutions are used over a longer period of time ('batch cleaning'), the degree of carbonation must be taken into account to determine the exact concentration or pH value, as the resulting soda has a greatly reduced cleaning effect, but simulates an excessively high concentration of the active cleaning agent.

Determine the sodium hydroxide (NaOH) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding normality up to the color change of phenolphthalein (pH 8.2).

   NaOH + HCl           →         NaCl      +   H₂O             colorless against phenolphthalein

2 NaOH + H₂SO₄      →         Na₂SO₄ + 2 H₂O

Determination of the soda ash (Na₂CO₃) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding normality up to the color change from methyl orange (pH 4.3).

   Na₂CO₃  + HCl        →       NaHCO₃  + NaCl

   NaHCO₃  + HCl        →      NaCl      + H₂O + CO₂    yellowish brown against methyl orange

2 Na₂CO₃   + H₂SO₄   →   2 NaHCO₃ + Na₂SO₄

2 NaHCO₃  + H₂SO₄    →  2 Na₂SO₄ + H₂O + 2 CO₂