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Lecture 7

CHM120H5 Lecture 7: Experiment 1.docx

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Thottackad Radhakrishnan

Experiment 1 Determination of the Product of a Redox Reaction: Reaction of Bromate and Hydroxylammonium ions Griselda Jonuzaj 1000580445 Section: 122 TA: Daniel Bouchard Date Performed: Thursday, January 16, 2014 Date Submitted: Wednesday, January 22, 2014 Introduction Titration is a key method of chemistry that can be used in many different ways to help uncover unknown amounts of products. One way titration is used is to determine the presence of Vitamin C in juices. This helps to establish the nutrition values that certain juices have or lack. The process includes using iodine and iodate solution in a redox titration with a starch indicator 1 acting as the endpoint of the titration . Purpose The goal of this lab was to identify the unknown product of the reaction and complete the redox reaction equation. (1) BrO3 + NH3OH + Br +? This goal was accomplished by using a known excess amount of bromate and a known amount of Hydroxylammonium. Hydroxylammonium acted as the limiting reagent while the Bromate reacted with potassium iodide solution. - - + - - (2) BrO + 3I + 6H O 3 Br + 3I +39H O 2 The rest of the Iodine was titrated with thiosulphate until an endpoint was reached as indicated by the starch indicator. Knowing the amount of bromate initially and the excess, the reacted bromate could then be calculated. (3) I3+ 2S O 2 32- 3I + S O4 62- Finally, to find the unknown product, the electrons transferred could be calculated by the moles of the reactants and the oxidation states. Experimental Method 2 Refer to the lab manual for standardized procedure . Deviations included using precise concentrations of the following reactants, 0.0200 M of NH OHCL, 0.0200M of KBrO 3 3 and 0.1000 M of Na S2 2. 3ew techniques that were used included a specific type of titration called iodometric titration. This technique uses iodine ions to indicate the endpoint of the titration. In this case, the appearance of the iodine in our solution (as observed in Erlenmeyer flask by the yellow color) indicated the end of the titration. Results NH O3Cl Volume: 10mL (0.0200 ±0.0002M) KBrO 3 Flask 1: (burette readings) (0.0200±0.0002M) Initial: 11.21mL; final: 31.15mL Flask 2: Initial: 10.25mL; final: 30.15mL Flask 3: Initial: 31.74mL; final: 51.64mL Na 2 2 3 Flask 1: (burette readings) (0.1000±0.0005M) Initial: 10.71mL; final 24.54mL Flask 2: Initial: 20.52mL; final: 34.75mL Flask 3: Initial: 34.75; final: 50.46 Table 1. Data Collected Table 2. Calculating the average amount of KBrO reacte3. Trials Calculations 1 (a) Given: Volume KBrO = 0301994L Concentration KBrO = 030200M n= C x V n= (0.0200M) (0.01994L) -4 n= 3.99 x 10 mol of KBrO initi3lly (b) Given: Volume Na S 2 2 0301383L Concentration Na S 2 2 031000M n= C x V n= (0.1000M) (0.01383L) n= 1.383 x 10 mol of Na S O 2 2t 3eacted. It is important to know the amount of Sodium thiosulfate in the reaction because from it, the amount of excess amount of KBrO can be dete3mined. From the balanced equations, the moles of Sodium thiosulfate can be divided by 6 because it 3 takes 1 BrO to produce 3 Iodine’s, and 3 Iodine’s produces 6 Sulfates. 1.383 x 10 /6= 2.3 x 10 mol of excess KBrO 3 In order to find the amount of KBrO that actually reacted, the excess amount must 3 be subtracted from the total amount that was present initially. ∴ 3.99 x 10 – 2.3 x 10 = 1.69 x 10 mol KBrO that reacted. 3 -4 2 Total amount of reacted KBrO = 1.61 x310 mol. 3 Total amount of reacted KBrO = 1.36 x310 mol. -4 Average The average of KBrO that r3acted throughout the 3 trials was: (1.69 x 10 + 1.61 x 10 + 1.36 x 10 )/3 -4 = 1.55 x 10 mol of reacted KBrO 3 2) - (a) To find oxidation state of Bromine in the compound BrO , let x be the 3xidation state of Br; x+ (-6) = -1 x= +5, this is the oxidation state of Br. In order to get a -1 charge of Br in the reactants side, each Bromine atom in BrO must ga3n a total of 6 electrons. (b) Moles of electrons transferred is the average amount in mol of BrO found in questi3n 1 multiplied by 6 because that is how many electrons must be transferred by each Bromine atom. The purpose of this step is to find how many moles of electron
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