Properties, Theories, and Reactions of Acids and Bases in Chemistry

What are the properties of aqueous acidic solutions?

They have a sour taste, change indicators (blue litmus to red), react with metals to generate hydrogen, react with metal oxides and hydroxides to form salts and water, and conduct electricity.

What are the properties of aqueous basic solutions?

They have a bitter taste, slippery feel, change indicators (red litmus to blue), react with acids to form salts and water, and conduct electricity.

According to the Arrhenius Theory, what defines an acid?

An acid is a substance that contains hydrogen and produces H+ in aqueous solutions.

According to the Arrhenius Theory, what defines a base?

A base contains the hydroxyl (OH) group and produces hydroxide ions (OH-) in aqueous solutions.

What is a neutralization reaction?

It is the combination of H+ (or H3O+) with OH- to form H2O.

What are strong acids?

Strong acids ionize 100% in water, examples include HCl, HBr, HI, H2SO4, HNO3, HClO4, and HClO3.

What are strong bases?

Strong bases ionize 100% in water, examples include LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2.

What is the hydrated hydrogen ion commonly referred to as?

The hydronium ion (H3O+).

In the Brønsted-Lowry Theory, what is an acid?

An acid is defined as a proton donor (H+).

In the Brønsted-Lowry Theory, what is a base?

A base is defined as a proton acceptor.

What are conjugate acid-base pairs?

They are two species that differ by a proton.

Identify the acid and conjugate base in the reaction: HNO3 + H2O → H3O+ + NO3-

HNO3 is the acid; NO3- is the conjugate base.

Identify the base and conjugate acid in the reaction: HNO3 + H2O → H3O+ + NO3-

H2O is the base; H3O+ is the conjugate acid.

What is the major difference between Arrhenius and Brønsted-Lowry theories?

The reaction does not have to occur in an aqueous solution, and bases are not required to be hydroxides.

What is autoionization of water?

It is the reaction where one water molecule acts as a base and another as an acid.

What is an amphoteric species?

A species that can behave as either an acid or a base.

Give an example of an amphoteric species.

Hydroxides of elements with intermediate electronegativity, such as Zn(OH)2.

How does bond strength relate to the strength of binary acids?

Acid strength increases with decreasing H-X bond strength.

What is the trend in acid strength for hydrohalic binary acids?

HF << HCl < HBr < HI; the stronger the H─X bond, the weaker the acid.

What is the acid leveling effect?

It states that the strongest acid that can exist in water is H3O+; stronger acids react with water to produce H3O+.

What is the strongest base that can exist in water?

OH- (hydroxide ion).

What are ternary acids?

Hydroxides of nonmetals that produce H3O+ in water, consisting of H, O, and a nonmetal.

What is the significance of the H's in ternary acids?

The H's are attached to O atoms, even though the formulas are written as HClO4 or H3PO4.

What is the general formula for ternary acids?

Ternary acids are represented as HxY(=O)z, where H's are attached to O atoms.

How does acid strength vary for binary acids?

Acid strength increases with decreasing H-X bond strength.

What trend is observed in the strength of ternary acids?

Strong ternary acids have weaker H-O bonds than weak ternary acids.

What factors increase the strength of ternary acids?

An increasing number of O atoms on the central atom and an increasing oxidation state of the central atom.

How does the electronegativity of the Y atom affect oxyacid strength?

The more electronegative the Y atom, the stronger the oxyacid, as it weakens the H-O bond.

What is the relationship between oxidation number and oxyacid strength?

The larger the oxidation number of the central atom, the stronger the oxyacid.

How does the number of oxygens attached to Y affect oxyacid strength?

The more oxygens attached to Y, the stronger the oxyacid, as it further weakens and polarizes the H-O bond.

What is the trend in strength for Cl ternary acids?

HClO < HClO2 < HClO3 < HClO4, from weakest to strongest.

What are the four combinations of acid-base reactions in aqueous solutions?

1. Strong acids - strong bases, 2. Weak acids - strong bases, 3. Strong acids - weak bases, 4. Weak acids - weak bases.

What is formed when a strong acid reacts with a strong base?

Soluble salts are formed.

What is an example of a strong acid reacting with a strong base?

Hydrobromic acid (HBr) reacting with calcium hydroxide (Ca(OH)2).

What is an acidic salt?

An acidic salt is formed by the reaction of polyprotic acids with less than the stoichiometric amount of base.

What is a basic salt?

A basic salt is formed by the reaction of polyhydroxy bases with less than the stoichiometric amount of acid.

What defines a Lewis acid?

A Lewis acid is defined as an electron pair acceptor.

What defines a Lewis base?

A Lewis base is defined as an electron pair donor.

What is the significance of coordinate covalent bonds in Lewis theory?

Neutralization reactions are accompanied by coordinate covalent bond formation.

What is the reaction of ammonia and hydrobromic acid an example of?

It is an example of both a Lewis and Brønsted-Lowry acid-base reaction.

How are binary acids prepared?

By reacting the nonmetallic element with H2 in the presence of UV light.

How are ternary acids formed?

By reacting nonmetal oxides (acid anhydrides) with water.

What is the reaction of sulfuric acid and sodium hydroxide in a 1:1 ratio?

H2SO4(aq) + NaOH(aq) → NaHSO4(aq) + H2O(ℓ), forming an acidic salt.

What is the reaction of barium hydroxide and hydrochloric acid in a 1:1 ratio?

Ba(OH)2(aq) + HCl(aq) → Ba(OH)Cl(aq) + H2O(ℓ), forming a basic salt.

What is the role of acidic and basic salts in neutralization?

Both can neutralize acids and bases, but the resulting solutions are either acidic or basic.

What is the relationship between the number of O atoms and the oxidation state of the central atom in ternary acids?

Every additional O atom increases the oxidation state of the central atom by 2.

What is the molecular equation for nitrous acid reacting with sodium hydroxide?

HNO2(aq) + NaOH(aq) → NaNO2(aq) + H2O(ℓ).

Molarity

The concentration of a solution expressed as moles of solute per liter of solution.

Balanced reaction

A chemical equation in which the number of atoms for each element is the same on both sides of the equation.

Total volume of solution

The sum of the volumes of all components mixed together.

Sodium sulfate amount

The quantity of sodium sulfate produced in a reaction, measured in millimoles (mmol).

Concentration of resulting solution

The molarity of the solution after mixing reactants.

Potassium hydroxide amount

The quantity of potassium hydroxide present after a reaction, measured in millimoles (mmol).

Potassium sulfate amount

The quantity of potassium sulfate produced in a reaction, measured in millimoles (mmol).

Volume required for neutralization

The volume of a solution needed to completely react with another solution.

Titration

A method of determining the concentration of one solution by reacting it with a solution of known concentration.

Primary standard

A chemical compound which can be used to accurately determine the concentration of another solution.

Standard solution

A solution whose concentration has been determined using a primary standard.

Standardization

The process in which the concentration of a solution is determined by accurately measuring the volume of the solution required to react with a known amount of a primary standard.

Indicator

A substance that exists in different forms with different colors depending on the concentration of H+ in solution.

Equivalence point

The point at which stoichiometrically equivalent amounts of the acid and base have reacted.

End point

The point at which the indicator changes color and the titration is stopped.

Potassium hydrogen phthalate (KHP)

A very good primary standard with a molar mass of 204.2 g/mol.

Percent purity

The percentage of a sample that is pure substance, calculated from the mass of the pure substance and the total mass of the sample.

Oxidation

An increase in the oxidation number, corresponding to the loss of electrons.

Reduction

A decrease in the oxidation number.

Oxidation number

A value that represents the total number of electrons an atom either gains or loses to form a chemical bond.

Half-reaction

A representation of either the oxidation or reduction process in a redox reaction.

OILRIG

A mnemonic for remembering that Oxidation Is Loss and Reduction Is Gain of electrons.

Balancing Redox Reactions

The process of making sure that the number of atoms and the charge are the same on both sides of a chemical equation.

Stoichiometry coefficients

Numbers placed in front of compounds in a balanced chemical equation to indicate the ratio of reactants and products.

H2O

Water, used to balance oxygen in half-reactions.

H+

Hydrogen ion, used to balance hydrogen in acidic solutions.

OH-

Hydroxide ion, used to neutralize H+ in basic solutions.

Electrons (e-)

Negatively charged particles that are involved in oxidation and reduction processes.

Example 11-12

Tin (II) ions are oxidized to tin (IV) by bromine using the half-reaction method.

Example 11-13

Dichromate ions oxidize iron (II) ions to iron (III) ions and are reduced to chromium (III) ions in acidic solution.

Redox Titrations

Calculations performed to determine the concentration of a solution based on redox reactions.

0.200 M KMnO4

A potassium permanganate solution with a molarity of 0.200, used in redox titrations.

0.150 M HCl

A hydrochloric acid solution with a molarity of 0.150, used in redox titrations.

40.0 mL of iron (II) sulfate

A specific volume of iron (II) sulfate solution that is oxidized to iron (III) in a redox reaction.

20.0 mL of 0.100 M potassium dichromate

A potassium dichromate solution with a molarity of 0.100, used to oxidize iron (II) sulfate.

Concentration of iron (II) sulfate solution

The amount of solute present in a given volume of iron (II) sulfate solution.

Half-Reaction Method

A method for balancing aqueous redox equations in acidic solution.

Oxidation State

A measure of the degree of oxidation of an atom in a substance.

Step 1

Assign oxidation states to all atoms and identify the substances being oxidized and reduced.

Step 2

Separate the overall reaction into two half-reactions: one for oxidation and one for reduction.

Oxidation Half-Reaction

Fe2+(aq) → Fe3+(aq)

Reduction Half-Reaction

MnO4-(aq) → Mn2+(aq)

Step 3

Balance each half-reaction with respect to mass.

Balancing Mass

Balance all elements other than H and O, then balance O by adding H2O, and balance H by adding H+.

Step 4

Balance each half-reaction with respect to charge by adding electrons.

Charge Balance for Oxidation

Fe2+(aq) → Fe3+(aq) + 1 e-

Charge Balance for Reduction

5 e- + 8 H+(aq) + MnO4-(aq) → Mn2+(aq) + 4 H2O(l)

Step 5

Make the number of electrons in both half-reactions equal by multiplying one or both half-reactions.

Final Oxidation Half-Reaction

5 Fe2+(aq) → 5 Fe3+(aq) + 5 e-

Final Reduction Half-Reaction

5 e- + 8 H+(aq) + MnO4-(aq) → Mn2+(aq) + 4 H2O(l)

Step 6

Add the two half-reactions together, canceling electrons and other species as necessary.

Step 7

Verify that the reaction is balanced with respect to both mass and charge.

Practice Problem

Balance the redox reaction in acidic solution: Cu(s) + NO3-(aq) → Cu2+(aq) + NO2(g)