Show all work 11. (12 points) Neutral red is an acid/base indicator, which is a
ID: 589008 • Letter: S
Question
Show all work 11. (12 points) Neutral red is an acid/base indicator, which is a wine-red color when pro- . It has a pKa -6.7. The tonated and an orange-ycllow color when deprotonated protonated form of neutral red abosorbs at 620 nm. The deprotonated for does not (a) (3 points) You make a 0.500 mM solution of neutral red at a pH of 7.4. This (b) (6 points) You are given a 0.500 mM sample of neutral red at an unknown pH. The (c) (3 points) What will be the absorbance of a 0.500 mM sample of neutral red at phH absorb at this wavelength. solution has an absorbance of 0.291. Calculate the molar absorptivity of neutral red at the wavelength (assume a 1 cm cuvette). absorbance of the solution is 0.421. Calculate the pH of the solution. 6.7Explanation / Answer
a)
A = e*l*C
A = absorbance of sample
e is the molar absorptivity , the typical units are 1/M-cm
l size of cuvette, typically reported in cm
c is the molar concentration, in mol per ltier or M
0.291 = e*1*(0.5*10^-3)
e = 0.291 /(10^-7.4)
e = 7309589.51
b)
get:
A = e*l*C
C = A/(e*l)
C = (0.421)/(7309589.51*1)
C = 5.7595*10^-8
[H+] = C= 5.7595*10^-8
pH = -log(5.7595*10^-8) = 7.2396
c)
pH = 6.7
[H+] = 10^-pH = 10^-6.7
A = e*l*C
A = (7309589.51)(1)(10^-6.7) =
A = 1.458