25.8 mg benzene 250 mL solution 256 nm 0.266 molar absorptivity

25.8 mg benzene 250 mL solution 256 nm 0.266 molar absorptivity

 

 

25.8 mg of benzene (C6H6, MW 78.11 g/mol) is dissolved in enough to make 250 mL of solution. The benzene absorbs at a wavelength of 256 nm, while the solvent (hexane) has negligible absorbance. The absorbance of the solution at 256 nm is 0.266 A.U. The path length of the sample cell is 1.00 cm. What is the molar absorptivity coefficient (ε) of benzene at 256 nm in units of M^-1 cm^-1?

 

 

A 250 mL solution dissolved with 25.8 mg of benzene (C6H6) has an absorption at 256 nm of 0.266 in a 1.0 cm cell. What is the molar absorptivity?

 

 

 

C6H6의 몰질량 = 78.11 g/mol 이므로,

25.8 mg 벤젠의 몰수를 계산하면,

(25.8 mg) (1 g / 1000 mg) (1 mol / 78.11 g)

= (25.8) (1 / 1000) (1 / 78.11)

= 0.0003303 mol

 

 

 

벤젠 용액의 몰농도

= 용질 mol수 / 용액 L수

= 0.0003303 mol / (250/1000 L)

= 0.00132 M

 

 

 

A = ε • C • L

> A = 흡광도

> ε = 몰흡광계수

> C = 몰농도(M)

> L = 시료 용기의 길이(cm)

( 참고 https://ywpop.tistory.com/12905 )

 

 

 

ε = A / (C • L)

= 0.266 / (0.00132 M × 1.00 cm)

= 201.5 /M•cm

 

 

 

답: 202 M^-1 cm^-1

 

 

 

 

[참고]

몰농도 = (25.8) (1 / 1000) (1 / 78.11) / (250/1000)

= 0.0013212 M

 

ε = 0.266 / (0.0013212 × 1.00)

= 201.33 /M•cm

 

 

 

 

[키워드] 벤젠의 흡광도 기준, 벤젠의 몰 흡광 계수 기준, 벤젠의 몰흡광계수 기준