GRE Subject Test: Chemistry : GRE Subject Test: Chemistry

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

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Example Questions

Example Question #12 : Analyzing Solids

Calculate the molar solubility of  with  in a solution containing  .

Possible Answers:

Correct answer:

Explanation:

The equation for the dissolution of  in water is below: 

The  for the above equation is:

Due to the solubility of  in water, taking into account the concentration of  from  and  can be set to:

The  concentration will be double the concentration of the  coming from :

Using an ICE table to process the data:

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Plugging these variables into the  equation gives:

Therefore, the  equation can be approximated to:

Therefore, the solubility of   in water is .

Example Question #13 : Analyzing Solids

 has a  equal to . What would be the numerical expression used to determine the molar solubility (S) of ?

Possible Answers:

Correct answer:

Explanation:

The equation for the dissolution of  in water is below: 

The Ksp expression for the above chemical equation is: 

Rearranging this equation to solve for solubility (S) gives:

Plugging the value for Ksp into the equation gives:

Example Question #321 : Gre Subject Test: Chemistry

For the titration of  with  solution of , the end point occurs upon addition of  of the  solution. Determine the initial concentration of chloride that was present in the original solution.

Possible Answers:

Correct answer:

Explanation:

The equivalence point is when enough titrant has been added so that the number of moles of titrant equals the number of moles of analyte. We must first determine the number of moles of silver ions at the equivalence point.

At the equivalence point the following occurs in solution:

The number of moles of silver ions at equivalence point is calculated as follows:

Plugging these values into the equation gives:

Example Question #21 : Solubility And Ions

How many moles of fluoride ions are present in  of a completely saturated solution of lead (II) fluoride?

Possible Answers:

Correct answer:

Explanation:

Recall that the solubility product constant is given by the equation below, for a reaction in the following format.

Using our balanced reaction, we can find the solubility product equation for the dissociation of lead (II) fluoride.

For each molecule of lead (II) fluoride that dissolves, it produces one lead ion and two fluoride ions. We can conclude that the concentration of fluoride ions in solution will be twice the concentration of lead ions.

Use these variables in the solubility product equation, along with the given value from the question.

Now we can solve for the value of .

Remember that this value is equal to the concentration of lead ions in solution and half the concentration of fluoride ions in solution.

Example Question #51 : Analytical Chemistry

Calculate the molar solubility of  which has a .

Possible Answers:

Correct answer:

Explanation:

The equation for the dissolution of  in water is: 

The  for the above equation is:

Due to the solubility of  in water, the concentration of  can be set to:

Therefore the concentration of  should be double that of :

Plugging these variables into the  equation gives:

Now, we can solve for the x-variable by setting this value equal to the given .

Therefore, the solubility of  in water is .

Example Question #321 : Gre Subject Test: Chemistry

Determining the molecular ion peak (parent peak) in mass spectroscopy allows you to determine what characteristic of a mystery molecule?

Possible Answers:

Nuclear charge

Molecular weight

Functional groups

Molecular charge

Correct answer:

Molecular weight

Explanation:

The molecular ion peak is determined using mass spectrometry. The parent peak is formed when a mystery molecule does not fragment, and simply loses an electron. This means that the mass to charge ratio of this peak will allow us to determine the molecular weight of the compound.

Example Question #321 : Gre Subject Test: Chemistry

Which of the following statements is true concerning infrared spectroscopy?

Possible Answers:

An IR spectrometer shines infrared light on a compound and records the positions where the light is blocked by the compound. This results in the spectrum's peaks.

Functional groups can be identified by looking in the fingerprint region of the spectrum.

When the infrared light frequency matches the frequency of bond vibration in a molecule, a peak is recorded on the spectrum. 

IR spectroscopy is useful in determining the size and shape of a compound's carbon skeleton.

Correct answer:

When the infrared light frequency matches the frequency of bond vibration in a molecule, a peak is recorded on the spectrum. 

Explanation:

IR spectroscopy allows you to identify what functional groups are present in a compound. The IR spectrum is created by recording the frequencies at which a polar bond's vibration frequency is equal to the infrared light's frequency.

The fingerprint region is separate from the function group region, and generally corresponds to carbon-carbon or carbon-hydrogen interactions. While the spectrum can show what groups are present in a compound, it cannot be used to find the position of these groups or provide a carbon skeleton.

Example Question #1471 : Mcat Biological Sciences

Which of the following statements is true concerning infrared (IR) spectroscopy?

Possible Answers:

The fingerprint region is most easily used to determine the functional groups in the molecule

IR spectroscopy is used to determine the frequency of vibrations between atoms

IR spectroscopy is used to determine the shape of the carbon backbone

IR spectroscopy can be used to easily determine molecular mass

Correct answer:

IR spectroscopy is used to determine the frequency of vibrations between atoms

Explanation:

IR spectroscopy is most commonly used to determine the functional groups found in the molecule being observed. This is done by observing the vibration frequencies between atoms in the molecule. It does not easily reveal the size or shape of the molecule's carbon skeleton. Although the fingerprint region is unique for every molecule, it is very difficult to read when attempting to determine the molecule's functional groups. Most functional group peaks are observed in the functional group region adjacent to the fingerprint region.

Example Question #1472 : Mcat Biological Sciences

In IR spectroscopy, the vibration between atoms is caused by which of the following?

Possible Answers:

Dipole moments between atoms

The number of protons in a nucleus

The overall molecular weight of the molecule

The movement of electrons to higher energy levels

Correct answer:

Dipole moments between atoms

Explanation:

Infrared (IR) spectroscopy takes advantage of the electrical difference between atoms in a polar bond. These dipole moments, when exposed to infrared radiation, stretch and contract in what appears to be a vibrating motion between the atoms. The different vibrational frequencies in the molecule allow for the compound to be "read" using IR spectroscopy.

Example Question #1 : Laboratory Practices

Which of the following functional groups exhibits the highest frequency in an infrared (IR) spectrum?

Possible Answers:

Ketone

Alcohol

Ester

Nitrile

Aldehyde

Correct answer:

Alcohol

Explanation:

An alcohol (-ROH) exhibits a strong, broad absorbance peak at about 3500cm-1. A nitrile's (-RCN) characteristic absorbance peak is at about 2200cm-1. Carbonyl groups have strong, sharp peaks from 1700cm-1 to 1750cm-1, depending on the type of carbonyl group. For instance, an ester (-RCO2R'-) has an absorbance at about 1750cm-1, while a ketone (-ROR'-) has an absorbance at around 1710cm-1.

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