Question

PRE-LAB (5): EXPERIMENT #7, Redox and Spectrophotometric Determina 7, Redox and Spectrophotometric Determination of Manganese in order to analyze for manganese by photometry, Mn? in the sample is converted to deep purple MnO.. What reagent is used to bring about this oxidation 4420 2. (1) Write and balance the redox reaction for the oxidation of Mn(II) to Mn(VII). How many electrons are involved? 3. (1/2) Sometimes you get a brown precipitate during the oxidation step in this experiment. What is this precipitate? 4. (1) A 2.3x10^M standard solution of manganese prepared in this experiment had an absorbance of 0.514 at 530 nm. The unknown solution had an absorbance of 0.448 at the same wavelength. Calculate the concentration of the unknown in M. 5. (2) An unknown solid sample containing manganese was dissolved in acid and then taken through the steps of oxidation to permanganate. The resulting permanganate solution was diluted to 250 mL in a volumetric flask. This final diluted permanganate solution had an absorbance of 0.579 at 530 nm in a 1.00 cm cell. The molar absorptivity of permanganate at 530 nm is 2240 L/mole-cm. a) Calculate the Molarity of the diluted permanganate solution. b) Calculate the grams of Mn (At. Wt.=54.94) in the original solid sample.

Answer 1

Solutions 4 Reagent uned KIOy or I ou with H₂O medium- a Mn +2 +1 Our Mn. Our Balancing t. 10,- A All atom then of oxygen for this add Hoi i Ht add it for hydrogen .. (A Change, e' add for balancing charge to . Mutz 7440 - Ma Oybe. + 8H+ +56ão 2. Iowa Rohe Multiply eq Bxs Io: +420 and eq 0 x 2 and addi 2 Mnth + 5 104 + 3H₂O 2Mnou tha +6H+ are involved. Total 5X2 = 10 e leefrom Scanned with CamScanner

3 some times we get brown precipitate When Mn to lag to Mn +2 (ay) pale pink on brown solution, color - solution pru(1,01]*+20+ [Muc Hay can +26H Mno - 4 2H₂O itget dark brown ve on standing after few minuten - solution. 4.] Concentration = 2.3*10-4M - Absorbance = 0.514. at 530nm. Ao beery low A=kc Kin same for same wavelength. k= 0.514 - 2234.78261 M 2 - 2.3x10-4 concentration for 0.448 absorbance. CEA 0.448aa' TA 4 uge = 2 810-4M 2234.78261 Cs Scanner with Scanner

15 A = Ece t=2240 Ymole-com At Absorbance = unitbess made Et molar absorbity = 4 mod-cam e length = 1.00 cm la 99 0.579 = 2240 x 2X e i c = 0.579 -2:58 5X10-4 M २५५० b Molarity = Molen = 2.585x10-4M 1000 Mole = 2.585x10-4x250 More = 6:4625 x 10-5 more. Givenmates - 6,4625x105 do Moleculex mass Ma18 = 6.46 25X10 -5x54.94 (mass = 3.55810-3 gram [ Moros = 8.55 mg Please like the answer and give ux peting Scanned with CamScanner