Hydrogen Peroxide Determination by Redox Titration

Transcription

1 Hydrogen Peroxide Deterination by Redox Titration Background Redox titrations can be used for analytes that are oxidizable or reducible. A variety of applications are possible with this ethod, ranging fro the deterination of the SO 2 in wine to hydrogen peroxide content in disinfectant solutions. In anganoetric redox titrations the powerful oxidizing effect of potassiu peranganate is used to oxidize the analyte. Due to its strong color no indicator has to be used to detect the equivalence point visually. Reactions 5 Na 2 C 2 O H KnO 4 10 CO Na n H 2 O + 2 K + std. substance titrant reaction products g/ol g/ol 5 H 2 O H KnO 4 5 O n H 2 O + 2 K + analyte titrant reaction products g/ol g/ol Safety Always take the necessary safety precautions when working in the laboratory: work carefully; wear a lab coat, protective gloves and safety goggles. Hydrogen peroxide is corrosive and harful to your health. Potassiu peranganate is also harful to your health and sulphuric acid is corrosive. Tasks Use pure di-sodiu oxalate ( = g/ol, z = 2) to deterine the titer of the titrant KnO 4 c(1/5 KnO 4 ) = 0.1 ol/l. Prepare the saple solution by weighing g of di-sodiu oxalate accurately into a glass titration beaker on an analytical balance. Dilute the standard substance with 50 L of 5 % sulphuric acid solution and heat this solution in a water bath to around 70 C as the titration reaction is too slow at roo teperature. Titrate with a platinu ring electrode at this teperature until the equivalence point, which will be recognized by the autoated titrator, is reached. When perforing a anual titration, the equivalence point is reached as soon as the color of the saple solution turns peranently light pink in the presence of excess of KnO 4. Workshop 3 1 Powered by ETTLER TOLEDO

2 Calculate the titer and perfor this analysis at least three ties. Calculate the ean value, standard deviation (s) and relative standard deviation (srel) for this titer deterination. Deterine the hydrogen peroxide in the saple of disinfectant. Use the sae saple preparation and titration procedure as for the titer deterination but don't heat up the saple solution. Use a saple size of about 0.3 g. Deterine the hydrogen peroxide content (in %) at least three ties and calculate ean value, standard deviation (s) and relative standard deviation (srel). Waste disposal: Neutralize (ph 7) the aqueous solutions and dispose of it as special waste. Workshop 3 2 Powered by ETTLER TOLEDO

3 Hydrogen Peroxide Deterination by Redox Titration Equipent anual titration: - 1x Analytical balance - 1x anual burette (10 L) - 6x Titration beakers (glass beakers, e.g. 100 L) - 1x agnetic stirrer - 3x agnetic stirrer bars - 1x Heatable water bath Autoatic titration: - 1x Analytical balance - 1x ettler-toledo Easy Ox or Easy Pro titrator with 10 L burette and tubing - 1x EG40-BNC platinu ring sensor - 6x Titration beakers - 3x agnetic stirrer bars - 1x Heatable water bath Cheicals The quantities below were roughly estiated for 5 titer deterinations and 5 acetic acid deterinations. - 1 L deionized water (ainly for anual titration and rinsing) L potassiu peranganate solution c = 0.02 ol/l, c(1/5 KnO 4 ) = 0.1 ol/l (3.16 g solid potassiu peranganate in 1 L solution) L of 5 % sulphuric acid solution (50 g of sulphuric acid in 1 L solution) g di-sodiu oxalate of high purity (titration standard) - 2 g of disinfectant solution (diluted hydrogen peroxide solution with a H 2 O 2 content of about 3 %, available in pharacies) as saple Preparation - Prepare the titrant and sulphuric acid solution. - Rinse the burette of the autoatic titrator with titrant at least twice to dispel any air bubbles trapped in the burette and tubing. Coents - This ethod ay be slightly adapted depending on the disinfectant used and its hydrogen peroxide content. Teacher Inforation 3 Powered by ETTLER TOLEDO

4 Solution Calculation: t = VEQ c C 10 p z t: Titer of the titrant (no unit) : Weight of standard substance used for the deterination (in g, here: Na 2 C 2 O 4 ) VEQ: Titrant consuption at the equivalence point (in L) c: Noinal (equivalence) concentration of the titrant (in ol/l, here: KnO 4 c(1/5 KnO 4 ) = 0.1 ol/l) C: Constant (in g/ol, see equation above) : olar ass of the standard substance (in g/ol, here: Na 2 C 2 O 4, = g/ol) 10: Factor for g to g and % conversion (in g/(g %)) p: purity of the standard substance (in %) z: equivalent nuber (no unit, here: 2) Expected result: The titer should be around 1 for a fresh standard solution. Calculation: R = VEQ c t C 10 z R: Result, content (in %, here: acetic acid content) VEQ: Titrant consuption at the equivalence point (in L) c: Noinal (equivalence) concentration of the titrant (in ol/l, here: KnO 4 c(1/5 KnO 4 ) = 0.1 ol/l) t: Titer of the titrant, as deterined before (no unit) C: Constant (in g %/ol, see equation above) : Saple weight (in g) : olar ass of the analyte (in g/ol, here: hydrogen peroxide, = g/ol) 10: Factor for g to g and % conversion (in g/(g %)) z: equivalence nuber (no unit, here: 2) Expected result: Depending on the saple the hydrogen peroxide content should be around 3 %. Teacher Inforation 4 Powered by ETTLER TOLEDO

5 Exaple Di-sodiu oxalate with a purity of 99.5 % was used to perfor three titer deterinations. In the following table the saple size (), titration consuption (VEQ) and the calculated titer (t) are shown: Nr. VEQ t g L g L g L The calculation of the the first saple is shown below: g 10 p z = ol g 10 g = g % 99.5 % 2 ol t = VEQ c g L 0.1 ol L = g ol The ean value, standard deviation (s) and relative standard deviation (srel) were calculated fro the results of the three titer deterinations: ean: s: srel: 0.21 % For the hydrogen peroxide content deterination three saple solutions were prepared and titrated. The saple size (), the titrant consuption (VEQ) and the calculated hydrogen peroxide (R) contents for these three easureents are listed in the following table: Nr. VEQ R g L % g L % g L % The calculation for the first easureent is shown in detail: 10 z = g ol g % 10 g = g % 2 ol R = VEQ c t C = ol L g % L ol = % Teacher Inforation 5 Powered by ETTLER TOLEDO

6 As for the titer deterination, the ean, s and srel was calculated: ean: % s: % srel: 0.33 % Teacher Inforation 6 Powered by ETTLER TOLEDO