Question

Sample Spectra overla بیا ن م Absorbance (AU) ن ه ن و ن 200 500 Wavelength (nm Exp 6 Question 7 Read over your lab book "prelab" for this experiment paying particular attention to where it discusses UV absorption. There is also attached an additional chapter on using UV absorbance as an analytical tool. Look at the attached dibenzalacetone UV spectrum. Determine the absorbance max (A) from y-axis vs wavelength (x-axis). The concentration used was 25mg dibenzalacetone/SOmletoh of which Sml was taken and then dissolved in 10 ml ethanol in order to arrive at the correct molarity range. You can now calculate the absorption coefficiente from the equation; Nd molarity of solution l-cell length 1cm hint: convert mg to grams to moles, mi to liters for molarity conversion Based upon your findings, does the calculated t make sense for any particular isomer? Justify your conclusions

Answer 1

As you can see in the question itself that absorbance maximum is 3.6 and length of the cuvette is 1 cm .

(equation 1) we know absorbance and length we can find concentration from given information.

A= ech

CULCULATE CONCENTRATION

25mg in 50 ml etoh.

moles of dibenzalacetone = mass given/ molar mass of dibenzalacetone(molar mass = 234.29g/mol)

mole= .025/234.29=.000107 mol(rounded off)

concentration = moles/ volume (liter)

concentration= .000107/.05= .00214M

now it is given that .5ml was taken in 10 ml of ethanol

so apply M1V1=M2V2   (M1= .00214M,V1= .5ml,V2=10.5ml)

M2= .00214*.5/10.5= .0001019M= .000102M(rounded off)

now use equation 1

A= ech

=3.6/1*0.000102

$\varepsilon$=35294.12cm-1 M-1

Sample Spectra overlaid -- - - -- - -- - -- - -- - - Absorbance (AU) 300 400 500 Wavelength Gamed