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Chapter 18: Q18P (page 457)

A compound with molecular mass 292.16g/molwas dissolved in a 5 - mLvolumetric flask. A1.00 - mLaliquot was withdrawn, placed in a 10 - mLvolumetric flask, and diluted to the mark. The absorbance atwas in 0.427 i acuvet. The molar absorptivity at 340nm isε340=6130M-1cm-1

(a) Calculate the concentration of compound in the cuvet.

(b) What was the concentration of compound in the 5 - mL flask?

(c) How many milligrams of compound were used to make the 5 - mLsolution?

Short Answer

Expert verified

a) The concentration of compound in the cuvetc=6.97.10-5M

b) The concentration of compound in the 5 - mL flaskc=6.97.10-4Mc

c) The milligrams of compound used to make the 5 - mL solution m = 1.02mg

Step by step solution

01

Define concentration

The concentration of a substance is the quantity of solute presentin a given quantity ofsolution. Concentrations are usually expressed in terms of molarity, defined as the number of moles of solute in 1 L of solution.

02

Concentration of compound

Diluted 10 times

c=6.97.10-4M

03

Concentration in Milligrams

n=3.48.10-6molMassm=n.M=3.48.10-6mol.292.16g/molm=1.02mg

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Most popular questions from this chapter

18-6. Box 3-1 showed a single-beam spectrophotometric ozone monitor. The emission spectrum of the mercury vapor lamp is shown in Box 18-2.

  1. What is the light source?
  2. What is the detector?
  3. What is the monochromator?
  4. What are the components of the optical pathlength, b?
  5. How does this instrument measure O3?

What is the purpose of neocuproine in the serum iron analysis?

Nitrite ionNO-2, is a preservative for bacon and other foods, but it is potentially carcinogenic. A spectrophotometric determination ofNO-2makes use of the following reactions

Here is an abbreviated procedure for the

determination:

1. To 50.0ml of unknown solution containing nitrite is added 1.00mL of sulfanilic acid solution.

2. After 10min , 2.00mL of 1 –a minonaphthalene solution and 1.00 mL of buffer are added.

3. After 15 min, the absorbance is read at 520 nm in a 5.00-cm cell.

The following solutions were analyzed:

A. 50.0 mL of food extract known to contain no nitrite (that is, a negligible amount); final absorbance =0.153.

B. 50.0mL of food extract suspected of containing nitrite; final absorbance \(=0.622\).

C. Same as B, but with 10.0μLof7.50×10−3MNaNO2added to the 50.0-mL sample; final absorbance =0.967.

(a) Calculate the molar absorptivity, of the colored product. Remember that a \(5.00\)-cm cell was used.

(b) How many micrograms ofNO-2were present in 50.0mL of food extract?

18-26. A 2.00mL solution of apotransferrin was titrated as illustrated in Figure 18-11. It required 163L of 1.43 mM ferric nitrilotriacetate to reach the end point.

(a) Why does the slope of the absorbance versus volume graph change abruptly at the equivalence point?

(b) How many moles of Fe(III) (= ferric nitrilotriacetate) were required to reach the end point?

(c) Each apotransferrin molecule binds two ferric ions. Find the molar concentration of apotransferrin in the 2.00mL solution.

Preparing standards for a calibration curve.

(a) How much ferrous ethylene diammonium sulfate(FeH3NCH2CH2NH3SO42⋅4H2O,FM382.15)should be dissolved in a 500mL volumetric flask with1MH2SO4to obtain a stock solution with~500μgFe/mL2?

(b) When making stock solution (a), you actually weighed out 1.627 g of reagent. What is the Fe concentration in role="math" localid="1668357579931" 500μgFe/mL2?

(c) How would you prepare 500 mL of standard containing 1,2,3,4, and5μgFe/mL2in0.1MH2SO4infrom stock solution (b) using any Class A pipets from Table 2-4 with only 500 -mL volumetric flasks?

(d) To reduce the generation of chemical waste, describe how you could prepare 50 mL of standard containing, andinfrom stock solution (b) by serial dilution using any Class A pipets from Table 2-3 with only 50mL volumetric flasks?
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