Instrumentation in Chemistry

For what purpose do scientists use Infrared Spectrophotometry?

• Identify organic compounds

• Identify inorganic compounds

• Determine concentration of an absorbing compound

• Separate & identify small quantities from mixtures

Answer explanation

This is the IR spec for ethanol

For what purpose do scientists use Ultraviolet and Visible light spectrophotometry?

• Identify organic compounds

• Identify inorganic compounds

• Determine concentration of an absorbing compound

• Separate & identify small quantities from mixtures

Answer explanation

As you can see, there's only one peak for this compound, so you'd use this chart to determine what wavelength to use in a Beer-Lambert study.

For what purpose do scientists use nuclear magnetic spectroscopy?

• Determine the fine structure of a compound containing hydrogen

• Determine fine structure of compounds that do not contain hydrogen

• Determine concentration of an absorbing compound

• Separate & identify small quantities from mixtures

Answer explanation

This is the proton magnetic resonance trace for ethanol. Note the formula CH₃CH₂OH shows 3 kinds of hydrogen.

For what purpose do scientists use paper chromatography?

• Determine molar mass of a compound

• Determine fine structure of organic compounds

• Separate chemicals in a mixture for identification purposes

• Separate chemicals in a mixture for further processing of each

Answer explanation

Once the chemicals have separated, you can cut out each chemical, dissolve in a liquid, and do other investigations on each.

 $Abs=4.301\left[conc\right]+.002$  Pictured is a Beer-Lambert calibration curve for chrysin in a compatible solvent. The best fit line has the equation shown above. What is the concentration of the compound if absorbance is 0.83?

Answer explanation

Solve equation for concentration. Subtract 0.002 from absorbance and divide by slope

When running a gas chromatography separation, what is the typical volume of mixture or liquid that is injected into the device?

• 1 milliliter

• 1 microliter

• 1 deciliter

• 1 picoliter

What is the most important criterion for choosing a carrier gas for a gas chromatography investigation?

• it must never be air

• it must be completely inert

• it must have the lowest possible molar mass

• it must not react with any of the chemicals or solvents being run through the device

Answer explanation

note on this diagram from "Dr. Ram" that there is a choice of carrier gases on the left.

In this IR spectrophotometer trace of acetone, you can clearly see the "peak" of absorbance around 1750 cm^-1, showing the typical carbonyl absorbance. Which of these molecules is acetone?

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Answer explanation

Carbonyl groups are found in ketones, aldehydes and carboxylic acids like acetic acid.

Can an investigator use gas chromatography to determine the approximate percentage of a compound in a mixture of two compounds?

• No

• Yes, if there is a difference in the rate at which the compounds move in the column

• Yes, if the compounds in the mixture react with each other

• Yes, but only if the two compounds are isomers of each other, and so have the same molar mass

What type of electromagnetic radiation is used in nuclear magnetic resonance spectrometry?

• UV-visible waves

• Infrared waves

• X-ray

• radio waves

Answer explanation

And the magnetic fields must be very strong. This is a device from Jeol company.