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Chapter 18: Q33P (page 459)

What is the difference between luminescence and Chemi-luminescence?

Short Answer

Expert verified

Chemi-luminescence is a type of luminescence that occurs during chemical reactions in some substances.

Luminescence is the emission of electromagnetic radiation (mostly light, but also ultraviolet and infrared radiation) which is not excited by a thermal process and elevated temperature of the substance but is due to receiving energy in some other form.

Step by step solution

01

Chemi-luminescence:

Chemiluminescence is the release of light from a chemical reaction.

02

Luminescence:

Luminosity is the sudden release of light by a substance not produced by heat; Or "cold light". It is therefore a form of cold body radiation.

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Most popular questions from this chapter

In formaldehyde, the transition n鈫�蟺*(T1)occurs at 397 nm,and the n鈫�蟺*(S1)transition comes at 355 nm. What is the difference in energy (kJ/mol) between the S1andT1states? This difference is due to the different electron spins in the two states.

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 鈥揳 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 10.0渭Lof7.50脳10鈭�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?

Vapor at a pressure of 30.3渭迟bar from the solid compound pyrazine had a transmittance of 24.4% at a wavelength of 266nm in

a 3.00 - cm cell at 298K

Pyrazine

(a) Convert transmittance to absorbance.

(b) Convert pressure to concentration (mol/L) with the ideal gas law (Problem 1-18).

(c) Find the molar absorptivity of gaseous pyrazine at 266nm.

Gold nanoparticles (Figure 17-31) can be titrated with the oxidizing agent TCNQ in the presence of excess ofBr2-to oxidize Au(0)"toAuBr2-in deaerated toluene. Gold atoms in the interior of the particle are Au(0) . Gold atoms bound to C12H25S- (dodecanethiol) ligands on the surface of the particle are Au(I) and are not titrated.

The table gives the absorbance at $856 0.700 mL of 1.00脳10-4MTCNQ+0.05M(C8H17)4N+Br-in toluene is titrated with gold nanoparticles (1.43 g/Lin toluene) from a microsyringe with a Teflon-coated needle. Absorbance in the table has already been corrected for dilution.

(a) Make a graph of absorbance versus volume of titrant and estimate the equivalence point. Calculate the Au(0) in 1.00 g of nanoparticles.

(b) From other analyses of similarly prepared nanoparticles, it is estimated that 25 % of the mass of the particle is dodecanethiol ligand. Calculate mmol of localid="1667559229564" C12H25Sin 1.00 g of nanoparticles.

(c) The Au(I) content of 1.00 g of nanoparticles should be 1.00 mass of Au(0) - mass of C12H25S. Calculate the micromoles of Au(I) in 1.00 g of nanoparticles and the mole ratio Au(I) :. In principle, this ratio should be 1: 1. The difference is most likely because C12H25Swas not measured for this specific nanoparticle preparation.

What is the difference between a fluorescence excitation spectrum and a fluorescence emission spectrum? Which one resembles an absorption spectrum?
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