AP Chemistry : pH and POH of Strong Acids and Bases

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #71 : Acid Base Reactions

Which of the following salts, when added to water, will result in a basic solution?

Possible Answers:

Potassium chloride

Ammonium bromide

Sodium chloride

Sodium fluoride

Correct answer:

Sodium fluoride

Explanation:

A salt will dissociate completely in an aqueous solution, forming its respective ions. Knowing this, we can make predictions on how the ions will affect the pH of the solution, given their strengths as conjugate acids and bases. Fluoride ions are the conjugate base of hydrofluoric acid, which is a weak acid. As a result, fluoride ions will attach to protons in solution and decrease the proton concentration of the solution. This will make the solution more basic.

Chloride and bromide ions are conjugate bases of strong acids. Since these strong acids would dissociate completely in water, these ions will not associate with hydrogen ions in solution and will not affect the solution pH.

Example Question #72 : Acid Base Reactions

Consider the following chemical reaction.

What phenomena is this responsible for?

Possible Answers:

When an acid and a base are mixed, a violent reaction occurs

Acid rain

The violent reaction between baking soda and vinegar

None of the available answers

Dry ice

Correct answer:

Acid rain

Explanation:

The above reaction describes the reaction that occurs when carbon dioxide dissolves in water and reacts to form carbonic acid, which is responsible for acid rain.

The phenomenon seen by dry ice is simply the sublimation of carbon dioxide. Acids and bases do not usually react in a violent fashion. The reaction between baking soda (sodium bicarbonate) and vinegar (acetic acid) is given below. The production of carbon dioxide gas is responsible for the bubbles seen in this reaction.

Example Question #72 : Acid Base Reactions

Which of the following is a pairing between an acid and its conjugate base?

Possible Answers:

PO4, PO3

H3O+, H20

H2CO3, CO2

H2O, COOH

Correct answer:

H3O+, H20

Explanation:

The conjugate base of an acid is the same formula, minus one proton. The only option that fits this description is the one that includes the hydronium ion (H3O+) and water (H2O).

Example Question #73 : Acid Base Reactions

Under which classification(s) of acid does  fall?

Possible Answers:

All of these

Arrhenius acid

Lewis acid

Brønsted-Lowry acid

Strong acid

Correct answer:

All of these

Explanation:

Every Lewis acid is also a Brønsted-Lowry acid, and every Brønsted-Lowry acid is an Arrhenius acid; thus, H2SO4 is all three, since it is an Arrhenius acid: (it dissolves in water to produce a proton). Sulfuric acid is also considered a strong acid, as it full dissociates in water.

Example Question #81 : Acid Base Reactions

In the following reaction, which is the conjugate acid? 

HCO3– + HCl → H2CO3 + Cl–

Possible Answers:

HCl

H2CO3

Cl–

HCO3–

Correct answer:

H2CO3

Explanation:

Conjugate acid has one more H+ than the compound with which it is being compared. Thus, H2CO3 is the conjugate acid of HCO3–.

Example Question #82 : Acid Base Reactions

Which of the following is not true of a neutralization reaction?

Possible Answers:

It is a specific double-displacement reaction.

There is a reaction between salt and water.

There is a reaction between acid and base.

It has 2 reactants and 2 products.

Correct answer:

There is a reaction between salt and water.

Explanation:

The PRODUCTS of a neutralization reactions are salt and water, not the reactants. The rest of the options all correctly pertain to neutralization reactions.

Example Question #83 : Acid Base Reactions

Which of the following chemical groups is expected to be found in a base?

Possible Answers:

Bicarbonate

Chloride

Hydrogen

Hydroxide

Carboxyl

Correct answer:

Hydroxide

Explanation:

Bases can be defined as species that quench hydrogen ions from a solution. A hydroxide ion and a hydrogen ion combine to form water in solution. Recall that basis solutions range in pH from about 7 to 14.

Example Question #84 : Acid Base Reactions

Which of the following groups is expected to be present in an acid?

Possible Answers:

Hydroxide

Chloride

Bicarbonate

Hydrogen

Carboxyl

Correct answer:

Hydrogen

Explanation:

Acids can be defined as species that donate hydrogen ions to solutions. If there is a hydrogen group on a molecule, it is possible that it may be donated to the solution, which will result in a decrease in pH. 

Example Question #85 : Acid Base Reactions

Which compound can be both a Bronsted-Lowry acid and Bronsted-Lowry base?

Possible Answers:

Correct answer:

Explanation:

The Bronsted-Lowry definition of an acid is a substance that can donate a hydrogen ion and forms its conjugate base; a Bronsted-Lowry base accepts a hydrogen ion and forms its conjugate acid. Thus we are looking for a substance that can either donate or accept a hydrogen ion (amphoteric). Bisulfite may give up a proton to become , a Bronsted-Lowry base. It acts as an acid as , which can donate up to two hydrogens.

Example Question #86 : Acid Base Reactions

Which of the following is a Lewis acid, but not a Bronsted-Lowry acid?

Possible Answers:

Correct answer:

Explanation:

For this question, we'll need to understand the different definitions of an acid in order to answer it. There are three definitions of acids that are important to know.

1. Arrhenius acids

These are compounds that, when added to water, increase the concentration of  ions present in solution.

2. Bronsted-Lowry acids

These are any acid that can release , even while not in water.

3. Lewis acids

This is the most general definition of acids. It is any compound that can accept a lone electron pair.

Lewis acids are the most general kind of acids, meaning that any acid that is Bronsted-Lowry or Arrhenius will also be a Lewis acid. However, the reverse is not true. Not all Lewis acids will fall under the category of Bronsted-Lowry or Arrhenius.

The correct answer in this question is aluminum chloride. We can see that, based on aluminum's position in the periodic table, it has three valence electrons in its outer shell. Each of these electrons is tied up in a shared bond with a chloride. This means that the aluminum in aluminum chloride has six valence electrons. However, since aluminum has a maximum capacity of eight valence electrons, it has room for two more. This vacancy allows the aluminum component of aluminum chloride to accept an electron pair from any sort of electron donor. Thus, aluminum chloride qualifies as a Lewis acid. However, aluminum chloride has no way of producing . Consequently, it is neither a Bronsted-Lowry acid nor is it an Arrhenius acid.

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