Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 19: Q6P (page 485)

Spectroscopic data for the indicators thymol blue (TB),semithymol blue (STB), and methylthymol blue (MTB) are shown in the table. A solution ofTB,STB,MTB in a1.000-cm cuvet had absorbances of 0.412at455nm,0.350 at485nm, and 0.632 at545nm. Modify the spreadsheet in Figure 19-4 to handle three simultaneous equations and find[TB],[STB]and[MTB]in the mixture.

Short Answer

Expert verified

TheTB,STB,MTBinthemixtureare,TB=1.22·10-5MSTB=9.30·10-6MMTB=1.32·10-5M

Step by step solution

01

Modify a spreadsheet and use a formula to find the values:

Make a spreadsheet,

Hence, highlight the cells G4,G5 and G6.

Use the formula in the cells,

=MMULT(MINVERSE(B4:D6);E4:E6)

Thus, the values of TB,STB,MTBare,

TB=1.22·10-5MSTB=9.30·10-6MMTB=1.32·10-5M

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

This problem can be worked with Equations 19-6 on a calculator or with the spreadsheet in Figure 19-4. Transferrin is the iron-transport protein found in blood. It has a molecular mass of 81 000 and carries twoFe3+ions. Desferrioxamine B is a chelator used to treat patients with iron overload (see the opening of Chapter 12). It has a molecular mass of about 650 and can bind oneFe3+Fe31. Desferrioxamine can take iron from many sites within the body and is excreted (with its iron) through the kidneys. Molar absorptivities of these compounds (saturated with iron) at two wavelengths are given in the table. Both compounds are colorless (no visible absorption) in the absence of iron.


(a) A solution of transferrin exhibits an absorbance of 0.463 at 470 nm in a 1.000-cm cell. Calculate the concentration of transferrin in milligrams per milliliter and the concentration of bound iron in micrograms per milliliter.

(b) After adding desferrioxamine (which dilutes the sample), the absorbance at 470 nm was 0.424, and the absorbance at 428 nm was 0.401. Calculate the fraction of iron in transferrin and the fraction in desferrioxamine. Remember that transferrin binds two iron atoms and desferrioxamine binds only one.

Figure 19-6 is a Scatchard plot for the addition of 0-20nM antigen X to a fixed concentration of antibodyP=(Po=10nM)Prepare a Scatchard plot from the data in the table and find K for the reactionP+X⇌PX. The table gives measured concentrations of unbound X and the complex PX. It is recommended that the fraction of saturation should span the range ,-0.2-0.8. What is the range of the fraction of saturation for the data?

Chemical equilibrium and analysis of a mixture. (Warning! This is a long problem.) A remote optical sensor for CO2in the ocean was designed to operate without the need for calibration.33


The sensor compartment is separated from seawater by a silicone membrane through which CO2, but not dissolved ions, can diffuse. Inside the sensor, CO2equilibrates with HCO3and CO32. For each

measurement, the sensor is flushed with fresh solution containingbromothymol blue indicator. All indicator is in the formnear neutral pH, so we can

write two mass balances:

[HIn−]+[ln2−]=FIn=50.0μMand[Na+]=FNα=50.0μM+42.0μM=92.0μM

has an absorbance maximum at 434 nm andhas a maximum at 620 nm. The sensor measures the absorbance ratio RA=A620/A434reproducibly without need for calibration. From this ratio, we can findin the seawater as outlined here:

(a).From Beer’s law for the mixture, write equations forin terms of the absorbance at 620 and 434 nmThen show that

[ln2−][Hln−]=RAε434HHn−−ε6,20Hln−ε620ln2−−RAε434ln2−=Rln (A)

(b) From the mass balance (1) and the acid dissociation constant

, show that

[Hln−]=F1nRln+1 (B)

[ln2−]=KlnFln[H+](Rln+1) (C)

(c) Show that H+=Kln/Rln (D)

(d) From the carbonic acid dissociation equilibria, show that

[HCO3−]=K1[CO(aq)]E[H+][CO32−]=K1K2[CO(aq)]F[H+]2

(e) Write the charge balance for the solution in the sensor compartment. Substitute in expressions B, C, E, and F forHln,In2-,[HCO3], and[CO32−]

(f) Suppose that the various constants have the following values:

ε4344HHn−=8.00×103M−1cm−1    K1=3.0×10−7ε6620Hn−=0    K2=3.3×10−11ε434ln2=1.90×103M−1cm−1    Kln=2.0×10−7ε620ln2−=1.70×104M−1cm−1    Kw=6.7×10−15

From the measured absorbance ratio=2.84, findin the seawater.

(g) Approximately what is the ionic strength inside the sensor compartment? Were we justified in neglecting activity coefficients in working this problem?

Iodine reacts with mesitylene to form a complex with an absorption maximum at 332 nm in CCl4 solution:

(b)Spectrophotometric data for this reaction are shown in the table.Because[mesitylene]tot>>[I2],we can say that [mesitylene]≈[mesitylene]tot. Prepare a graph ofA/([mesitylene][I2]tot)versusA/[I2]totand find the equilibrium constant and molar absorptivity of the complex.

The spreadsheet lists molar absorptivities of three dyes and the absorbance of a mixture of the dyes in a 1.000-cm cell. Use the least-squares procedure in Figure 19-3 to find the concentration of each dye in the mixture.
See all solutions

Recommended explanations on Chemistry Textbooks

Inorganic Chemistry

Read Explanation

Chemical Reactions

Read Explanation

Nuclear Chemistry

Read Explanation

Organic Chemistry

Read Explanation

Chemistry Branches

Read Explanation

Ionic and Molecular Compounds

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free