GRE Subject Test: Chemistry : IR Spectroscopy

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

Example Question #11 : Ir Spectroscopy

What is the absorbance of an IR peak with a \(\displaystyle 17\%\) transmittance?

Possible Answers:

\(\displaystyle 1.22\)

\(\displaystyle 0.77\)

\(\displaystyle 0.25\)

\(\displaystyle 0.25\)

Correct answer:

\(\displaystyle 0.77\)

Explanation:

\(\displaystyle \%T=\frac{I}{I_{o}}\times100=17\%\)

Therefore,\(\displaystyle T=\frac{I}{I_{o}}=0.17\)

Using the equation that relates absorbance to transmittance, we can convert 0.17 transmittance to absorbance:

\(\displaystyle A=-log(T)=-log(0.17)=0.77\)

Therefore the absorbance for this peak is 0.77.

Example Question #12 : Ir Spectroscopy

What is the absorbance of an IR peak with a \(\displaystyle 36\%\) transmittance?

Possible Answers:

\(\displaystyle 0.44\)

\(\displaystyle 0.85\)

\(\displaystyle 0.53\)

\(\displaystyle 0.12\)

Correct answer:

\(\displaystyle 0.44\)

Explanation:

\(\displaystyle \%T=\frac{I}{I_{o}}\times100=36\%\)

Therefore,\(\displaystyle T=\frac{I}{I_{o}}=0.36\)

Using the equation that relates absorbance to transmittance, we can convert 0.36 transmittance to absorbance:

\(\displaystyle A=-log(T)=-log(0.36)=0.44\)

Therefore the absorbance for this peak is 0.44.

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