GRE Subject Test: Chemistry : Acid-Base Chemistry

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

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Example Questions

Example Question #91 : Gre Subject Test: Chemistry

Considering the Ka for  is , what is the Kb for ?

Possible Answers:

Correct answer:

Explanation:

The equilibrium governing the dissolution of  in water is:

 is the conjugate acid of . In other words,  is the conjugate base of .

Using the relationship, , we can calculate the Kb.

Rearrange the equation and solve:

 

Example Question #11 : Acid Base Chemistry

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Based on the equilibrium shown, what does  act as? 

Possible Answers:

A cation

An acid

A base

A catalyst

A radical

Correct answer:

A base

Explanation:

A base is a substance that can accept a proton. The conjugate base of an acid is formed when the acid donates a proton. In this case,  is the conjugate base to the acid . This is because  donates a hydrogen ion to the organic molecule to form , the conjugate base.

Example Question #1 : Acid Base Reactions

Which of the following is the weakest acid?

Possible Answers:

Correct answer:

Explanation:

 (hydrofluoric acid) is the weakest acid. Fluoride ion is the most electronegative ion. Among the other halogens, its atomic radius is smaller, and therefore bonds more strongly with hydrogen and therefore does not completely dissociate in solution as compared to , , and . Perchloric acid is a strong acid and dissociates completely in solution.

Example Question #12 : Acid Base Chemistry

What is the type of reaction given?

Possible Answers:

Neutralization Reaction

Redox Reaction

Sublimation Reaction

Synthesis Reaction

Catalytic reaction

Correct answer:

Neutralization Reaction

Explanation:

The reaction given is called a neutralization reaction because the acid and base components react to counterbalance each other making them chemically neutral. This type of reaction occurs between an acid and base to form a water and a salt. A neutralization reaction between a strong acid and a strong base react to form a neutral solution of pH 7.

Example Question #11 : Acid Base Reactions

Based on the above balanced equation for a neutralization reaction, what is the concentration of a  solution if  of   is needed to neutralize a  solution of ?

Possible Answers:

Correct answer:

Explanation:

We need to convert milliliters to liters:

We need to determine the moles of  using dimensional analysis the concentration as a conversion factor:

Based on the chemical equation given:

We can used the relationship of moles of  and moles of  as a conversion factor to determine the moles of :

Concentration in molarity can be calculated using the following formula:

Let's convert liters of  to the mL:

Therefore, the concentration of  is:

Example Question #12 : Acid Base Reactions

Based on the above balanced equation for a neutralization reaction, how many moles of  is formed if  of   is needed to neutralize a solution of ?

Possible Answers:

Correct answer:

Explanation:

We need to convert milliliters of  to liters:

We need to determine the moles of  using dimensional analysis and the concentration as a conversion factor:

 Based on the chemical equation given:

We can use the relationship of moles of  and moles of  as a conversion factor to determine the moles of :

Example Question #11 : Acid Base Chemistry

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If 4.2 moles of  is reacted with 3.5 moles of , how many grams of  is produced?

Possible Answers:

Correct answer:

Explanation:

 is the limiting reactant because based on the equation,  and react in a 1:1 mole ratio. However, there is 0.5 moles more of  than  therefore the amount of  produced is limited by the amount of present in the reaction. Based on the equation for every 1 mole of  reacted, 1 mole of  was produced:

Therefore,

Example Question #101 : General Chemistry

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Determine the acid dissociation constant for a  monoprotic acid  dissolved in the  in which a pH meter for read pH  for the solution.

Possible Answers:

Correct answer:

Explanation:

The acid dissociation constant expression for this reaction is:

Due to the dissociation of :

Using the following equation, we can calculate the  concentration:

Plug the values obtained in to the acid dissociation constant expression:

Example Question #17 : Acid Base Chemistry

Which of the following pH values is an acceptable equivalence point for a weak base being titrated by a strong acid?

Possible Answers:

Correct answer:

Explanation:

The equivalence point is the point during a titration when there are equal equivalents of acid and base in the solution. Since a strong acid will have more effect on the pH than the same amount of a weak base, we predict that the solution's pH will be acidic at the equivalence point. 5.2 and 1.3 are both acidic, but 1.3 is remarkably acidic considering that there is an equal amount of base in the solution. As a result, 5.2 is a more appropriate answer.

The equivalence point for a strong acid and strong base will be 7.0. When one of the compounds is weak, however, it will dissociate less than its strong counterpart. In our case, the base will dissociate less than the acid. The acid, thus, contributes more to the pH character of the solution.

Example Question #1 : Titration Curves

A weak acid is slowly titrated with a strong base. Where on the titration curve would the solution be the most well-buffered?

Possible Answers:

The equivalence point

When no base has been added

When the amount of base added equals the amount of acid in the solution.

The half equivalence point

Correct answer:

The half equivalence point

Explanation:

At the half equivalence point, the concentration of acid in the solution is equal to the concentration of the conjugate base in solution. At this point, the graph shows a line that is near horizontal. This means that base or acid could be added and the pH of the solution would change very slowly.

Remember that pH is on the y-axis of the titration curve; thus a near-horizontal line will signify a region where pH is most stable. At the half equivalence point, pH = pKa.

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