3. An indicator is a dye whose spectrum changes with pH. Consider the following data for the absorption spectrum of an indicator (pK = 4) in its ionized and nonionized form. InH* + In + H* Molar absorptivity, ɛ (M1.cm-1) InH (nm) In 400 10,000 15,000 8,000 420 2,000 8,000 12,000 3,000 440 460 480

0 The acid-base indicator HIn undergoes the following reaction in dilute aqueous solution:HIn color1 m H1 1 In2color2The following absorbance data were obtained for a 5.00 3 1024M solution of HIn in 0.1 M NaOH and0.1 M HCl. Measurements were made at wavelengths of 485 nm and 625 nm with 1.00-cm cells.0.1 M NaOH A485 5 0.075 A625 5 0.9040.1 M HCl A485 5 0.487 A625 5 0.181In the NaOH solution, essentially all of the indicator is present as In2; in the acidic solution, it is essentiallyall in the form of HIn.(a) Calculate molar absorptivities for In2 and HIn at 485 and 625 nm.(b) Calculate the acid dissociation constant for the indicator if a pH 5.00 buffer containing a small amountof the indicator exhibits an absorbance of 0.567 at 485 nm and 0.395 at 625 nm (1.00-cm cells).(c) What is the pH of a solution containing a small amount of the indicator that exhibits an absorbance of0.492 at 485 nm and 0.245 at 635 nm (1.00-cm cells)?(d) A 25.00-mL aliquot of a solution of purified weak…

atWhat is [H30+] in a solution of 0.25 M CH3CO2H and 0.030 M NaCH3CO2? CH3CO,H(aq) + H,0(1) E H30*(aq) + CH3CO,¯(aq) Ka = = 1.8 × 10-5

An employer is interviewing 4 applicants for a job as a laboratory technician and askseach of them how to prepare a buffer solution with a pH close to 11.000.Use these ka’s to help you: Show your workPropionic Acid, CH3CH2COOH, ka = 1.34 x 10-5 Ethanamine, CH3CH2NH2, kb = 6.3 x 10-4 Jung says he would mix CH3CH2COOH & CH4CH3COOHDominique says she would mix CH3CH2 NH2 & CH3CH2COOHJoshua says he would mix CH3CH2COOH & CH3COONaKyla says she would mix CH3CH2NH2 & CH3CH2NH3BrWho would you hire based on their ability to make a buffer?_________________________

Questions 30-35 refer to the same weak acid/strong base (WA/SB) titration. Prior to the beginning of the titration, there were 0.0090 moles of hypobromous acid present in the flask. The Ką of hypobromous acid is 2.8 x 10-9. (Q30) A 30.00 mL solution of 0.300 M hypobromous acid (HBRO) is being titrated with a solution that is 0.600 M in lithium hydroxide (LIOH). What is the initial solution pH (i.e., when 0.00 mL of titrant have been added)?

Subject- chemistry

Consider the following infermation about sulfurous acid, a diprotic acid (11,S0,L LSO3=HSO, +1I* pK=1.81 HSO, S0,+H pK2-691 The titration curve for sodism sulfite, Na SO, with standard HCl is shown below PH VI V2 ml, HO added What are the major species present al point 3? O No

Consider the spectrophotometric pH measurement of seawater with the indicator thymol blue illustrated at the opening of this chapter. The blue form of the indicator In22 on page 202 has maximum absorbance at a wavelength of 596 nm (nanometers). The yellow form HIn2 has maximum absorbance at 435 nm. Measurements of absorbance at the two wavelengths allows us to find the ratio [In22]/[HIn2]. How would you use this measurement to find the pH?

-Buffer Preparation-

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