Chapter 2, Problem 6P

Treatment of ammonia with phenol in the presence of hypochlorite yields indophenol, a blue product that absrobs light at 625 nm, which çan be used for the spectrophotometric determination of ammonia. gan OCF OH + NH3 indophenol anion To determinè the ammonia concentration in a sample of lake water, three samples are prepared. In sample A, 10.0 mL of lake water is mixed with 5 mL of phenol solution and 2 mL of sodium hypochlorite solution, and diluted to 25.0 mL in a volumetric flask. In sample B, 10.0 mL of lake water is mixed with 5 mL of phenol solution, 2 mL of sodium hypochlorite solution, and 2.50 mL of a 5.50 x 10-4 M ammonia solution, and diluted to 25.0 mL. Sample C is a reagent blank. It contains 10.0 mL of distilled water, 5 mL of phenol solution, and 2 mL of sodium hypochlorite solution, diluted to 25.0 mL. The absorbance of the three samples is then measured at 625 nm in a 1.00 cm cuvette. The results are shown in the table. Sample Absorbance (625 nm) A 0.361 B 0.608 C…

WARIARTAM 2. 1.2589 g of a certain brand of milk powder required 25.89 mL of 0.01873M EDTA to titrate the calcium contained in the sample. (a) What is the percent calcium in the sample? (b) Would the true result be higher, lower, or not be affected if the milk powder sample has been slightly wet?

4. The molar absorptivities of the indicator weak acid HIn (K₁ = 1.42 x 105) and its conjugate base In at 570 were determined as ε(HIn) = 7120 and ɛ(In) = 961. The optical length b = 1.00 cm. (a) What is the absorbance of an unbuffered indicator solution having total indicator concentration 8.0 × 10%. (b) What is the absorbance of a buffered indicator solution having total indicator concentration 8.0 x 105 and pH = 6.5.