GRE Subject Test: Chemistry : Analytical Chemistry
Study concepts, example questions & explanations for GRE Subject Test: Chemistry
All GRE Subject Test: Chemistry Resources
Example Questions
Example Question #91 : Analytical Chemistry
Extraction is the process of removing compounds from a solution by taking advantage of varying solubilities. The process of extraction for a mixture of diethylamine, phenol, acetic acid, and ammonia involves three steps.
1. Add a strong acid and shake the solution. Let the aqueous layer drain off.
2. Add a weak base and shake the solution. Let the aqueous layer drain off.
3. Add a strong base and shake the solution. Let the aqueous layer drain off.
Which of the following compounds would be the last to enter the aqueous phase using this technique?
Acetic acid
Ammonia
Phenol
Water
Diethylamine
Phenol
Think about what will be reacting with each substance as it is introduced to the solution.
First, a strong acid is added. This will make all bases in the solution (ammonia and diethylamine) become protonated, allowing them to become soluble. They will transition to the aqueous phase and be removed.
Next, a weak base is added. Only carboxylic acids will be deprotonated by this addition, gaining a charge and transitioning to the aqueous phase. Acetic acid will be extracted.
Finally, a strong base will deprotonate the weak acids, such as phenol. As a result, phenol will be the last molecule to leave the solution.
Example Question #1 : Other Analytical Methods
Which of the following mixtures would not be adequately separated via distillation?
A solution of alcohols of different sizes
Racemic mixture
A solution containing three diastereomers
A solution of polar and nonpolar compounds
Racemic mixture
Distillation involves the separation of compounds by taking advantage of their different boiling points. Mixtures with similar boiling points would not be adequately separated using distillation.
A racemic mixture is a mixture of enantiomers, which have identical boiling points. As a result, distillation would not be effective for separating a racemic mixture.
Diastereomers will have differing physical properties and can be separated by boiling point. Larger alkane chains result in higher boiling points, allowing separation of different sized alcohols by distillation. Polar compounds will have greater intermolecular forces, generally leading to higher boiling points, and allowing them to be separated from nonpolar compounds.
Example Question #21 : Spectroscopy
Which formula gives the relationship between the energy (
There is a direct relationship between energy (
Example Question #22 : Spectroscopy
There are four laser pointers that give off different colors off light. The wavelengths corresponding to these colors are:
violet-
red-
green-
blue-
yellow-
Which laser pointer is expected to give off light with the highest energy?
Blue
Green
Violet
Red
Yellow
Violet
Violet waves have the most energy of the visible spectrum because of the relationship:
Where 
Therefore, there is an inverse relationship between wavelength and frequency. There is a direct relationship between energy and frequency governed by the equation
Where 
For the violet light:
If we complete this calculation for the other colors, our conceptual answer will be confirmed mathematically.
Example Question #21 : Spectroscopy
Which analytical method is used primarily to determine the functional groups present in a compound?
Nuclear magnetic resonance (NMR) spectroscopy
Infrared (IR) spectroscopy
More than one of these
Mass spectrometry
Ultraviolet-visible spectroscopy
Infrared (IR) spectroscopy
Infrared (IR) spectroscopy is used to determine the functional groups present in a molecule. It makes use of the IR region of the electromagnetic spectrum. When an analyte is exposed to IR radiation, different functional groups absorb radiation at their characteristic wavelengths causing vibrational and rotational excitation to bonds within the molecule. The frequencies absorbed correspond to the amount of energy required to increase the molecular vibration of the functional groups in a molecule and can be plotted on a graph for analysis. Mass spectroscopy is used primarily to determine the amount and types of chemicals present within a sample. Ultraviolet-visible spectroscopy is used to analyze highly conjugated compounds, biological molecules, and transition metals. NMR spectroscopy gives information about the electronic structure of a molecule.
Example Question #92 : Analytical Chemistry
In a UV-visible absorption spectroscopy experiment, the length of the cell or cuvette is 1cm. Given the calibration curve for a substance, what is the molar extinction coefficient for this compound?
The equation for Beer's law is:
Rearrange the equation:
Given that 
Certified Tutor
Certified Tutor
All GRE Subject Test: Chemistry Resources
