Chapter 9: Chemical Reactions in Aqueous Solutions

Flashcards covering general properties of aqueous solutions, electrolytes, precipitation, acid-base, and redox reactions, concentration, and chemical analysis calculations.

What is a solution?

A homogeneous mixture of two or more substances.

In a solution, what is the solvent?

The substance present in the largest amount (moles).

In a solution, what are the solutes?

The substances present in the solution other than the solvent.

What does it mean if a substance is soluble?

It means the substance dissolves in a particular solvent.

Unless otherwise noted, what does the term "solution" refer specifically to in Chapter 9?

An aqueous solution.

What is an electrolyte?

A substance that dissolves in water to yield a solution that conducts electricity.

What occurs during the process of dissociation?

An electrolyte breaks apart into its constituent ions.

What is ionization?

The process where a molecular compound forms ions when it dissolves.

What is a nonelectrolyte?

A substance that dissolves in water to yield a solution that does not conduct electricity.

How do sucrose molecules behave when dissolved in water?

The sucrose molecules remain intact upon dissolving.

What is a strong electrolyte?

An electrolyte that dissociates completely.

Which categories of substances are considered strong electrolytes?

Water soluble ionic compounds, strong acids, and strong bases.

What are the seven strong acids listed in Table 9.1?

$HCl$, $HBr$, $HI$, $HNO_3$, $HClO_3$, $HClO_4$, and $H_2SO_4$.

To what extent does the second ionization of sulfuric acid ($H_2SO_4$) occur?

It happens only to a very small extent.

What is a weak electrolyte?

A compound that produces ions upon dissolving but exists in solution predominantly as molecules that are not ionized.

What do weak electrolytes include?

Weak acids and weak bases.

What does the double arrow ($\rightleftharpoons$) denote in a chemical equation?

A reaction that occurs in both directions.

When is a reaction in a state of dynamic chemical equilibrium?

When both the forward and reverse reactions occur at the same rate.

How are sucrose and fructose classified regarding their electrolyte properties?

They are nonelectrolytes.

How are sodium citrate ($Na_3C_6H_5O_7$) and potassium citrate ($K_3C_6H_5O_7$) classified as electrolytes?

They are strong electrolytes.

How is ascorbic acid ($H_2C_6H_6O_6$) classified relative to its electrolyte properties?

It is a weak electrolyte (weak acid).

What are the only molecular compounds that are strong electrolytes?

The strong acids listed in Table 9.1.

What is a precipitate?

An insoluble product that separates from a solution.

What is a precipitation reaction?

A chemical reaction in which a precipitate forms.

Why is water an effective solvent for ionic compounds?

Because it is a polar molecule.

How are the partial charges distributed in a water molecule?

The oxygen atom is partially negative and the hydrogen atoms are partially positive.

What is hydration?

Occurs when water molecules remove individual ions from an ionic solid by surrounding them so the substance dissolves.

How is solubility defined?

The maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature.

What is a molecular equation?

An equation where compounds are represented by chemical formulas as though they exist in solution as molecules or formula units.

What are metathesis (or double replacement) reactions?

Reactions in which cations in two ionic compounds exchange anions.

What is an ionic equation?

An equation where compounds that exist completely or predominantly as ions in solution are represented as those ions.

What is a net ionic equation?

An equation that includes only the species that are actually involved in the reaction.

What are spectator ions?

Ions that appear on both sides of the equation and do not participate in the reaction.

What should be done if all reactants and products in a reaction are strong electrolytes?

Identify that all ions are spectator ions, meaning there is no net ionic equation and no reaction takes place.

What are the eight strong bases listed in Table 9.4?

$LiOH$, $NaOH$, $KOH$, $RbOH$, $CsOH$, $Ca(OH)_2$, $Sr(OH)_2$, and $Ba(OH)_2$.

Which groups' hydroxides constitute the strong bases?

The hydroxides of Group 1A and heavy Group 2A.

How is an Arrhenius acid defined?

A substance that ionizes in water to produce $H^+$.

How is an Arrhenius base defined?

A substance that dissociates in water to produce $OH^-$.

What is a Brønsted acid?

A proton donor.

What is a Brønsted base?

A proton acceptor.

In acid-base chemistry, what does a "proton" refer to?

A hydrogen atom that has lost its electron ($H^+$).

What ion is formed when Brønsted acids donate protons to water?

The hydronium ion ($H_3O^+$).

What is a monoprotic acid?

An acid that has one proton to donate.

What is a polyprotic acid?

An acid that has more than one acidic hydrogen atom.

What is a diprotic acid?

A polyprotic acid with two acidic hydrogen atoms, such as $H_2SO_4$.

What term describes bases that produce only one mole of hydroxide per mole of compound?

Monobasic.

What is a dibasic base?

A base that produces more than one hydroxide per mole of compound, such as $Ba(OH)_2$.

What is a neutralization reaction?

A reaction between an acid and a base.

What products are generally produced by a neutralization reaction?

Water and a salt.

What is the common net ionic equation for many acid-base reactions?

$$H^+(aq) + OH^-(aq) \rightarrow H_2O(l)$$

Why is milk of magnesia considered a suspension rather than a solution?

Because $Mg(OH)_2$ is insoluble in water; the undissolved solid remains suspended.

What is an oxidation-reduction (redox) reaction?

A chemical reaction in which electrons are transferred from one reactant to another.

What is oxidation?

The loss of electrons.

What is reduction?

The gain of electrons.

How is a redox reaction related to half-reactions?

A redox reaction is the sum of an oxidation half-reaction and a reduction half-reaction.

What is an oxidation number (or oxidation state)?

The charge an atom would have if electrons were transferred completely.

What is the oxidation number of an element in its elemental form?

$$0$$

In a neutral molecule, what must the sum of oxidation numbers equal?

$$0$$

In a polyatomic ion, what must the sum of oxidation numbers equal?

The charge on the ion.

What is the oxidation number of a monoatomic ion?

It is equal to the charge on the ion.

What is the oxidation number of fluorine in all its compounds?

$$-1$$

What are the standard oxidation numbers for Group 1 and Group 2 metals in compounds?

$+1$ for Group 1 and $+2$ for Group 2.

What is the common oxidation number of hydrogen in compounds?

$$+1$$

In which exception is the oxidation number of hydrogen $-1$?

When it is combined with a Group 1 or 2 metal to form a metal hydride (e.g., $LiH$ or $CaH_2$).

What is the common oxidation number for oxygen in compounds?

$$-2$$

What is the oxidation number of oxygen in peroxides like $H_2O_2$?

$$-1$$

What is the oxidation number of oxygen in the superoxide $KO_2$?

$$-1/2$$

What is the general oxidation number for Group 17 elements (other than fluorine) in compounds?

$$-1$$

What is the oxidation number of Manganese in $KMnO_4$?

$$+7$$

What is the oxidation number of Sulfur in $H_2SO_4$?

$$+6$$

What is the oxidation number of Carbon in the carbonate ion ($CO_3^{2-}$)?

$$+4$$

What is the oxidation number of Nitrogen in $N_2O_5$?

$$+5$$

What occurs in a displacement reaction?

An atom or an ion in a compound is replaced by an atom of another element.

What happens to a metal when it is oxidized by an aqueous solution?

It becomes an aqueous ion.

What is the activity series?

A list of metals (and hydrogen) arranged in order of decreasing ease of oxidation.

What are the metals at the top of the activity series commonly called?

Active metals.

What are the metals at the bottom of the activity series commonly called?

Noble metals.

What determines if an element in the activity series will be oxidized?

It will be oxidized by the ions of any element that appears below it in the series.

What two balances must be maintained in a redox reaction?

Mass balance and charge balance.

What must be balanced before adding two half-reactions?

The number of electrons.

What is a hydrogen displacement reaction?

A reaction in which hydrogen ion is reduced to hydrogen gas.

What is a combination reaction in the context of redox?

A reaction where elements combine, involving oxidation and reduction (e.g., $3H_2 + N_2 \rightarrow 2NH_3$).

What is a disproportionation reaction?

A reaction that occurs when one element undergoes both oxidation and reduction.

Why is combustion considered a redox process?

Because electrons are transferred, typically involving the oxidation of a fuel and reduction of oxygen.

How is Molarity ($M$) defined?

The number of moles of solute per liter of solution.

What is the equation to calculate moles from Molarity ($M$) and Volume ($L$)?

$$moles = M \times L$$

What is dilution?

The process of preparing a less concentrated solution from a more concentrated one.

What principle remains true during a dilution?

Moles of solute before dilution = moles of solute after dilution.

What is the mathematical equation for dilution?

$$M_1V_1 = M_2V_2$$

What is a serial dilution?

A series of dilutions used to prepare a number of increasingly dilute solutions.

What does the square bracket notation ($[X]$) represent?

Molar concentration.

How is pH defined?

The negative base-10 logarithm of the hydronium ion concentration (in $mol/L$).

What is the equation for pH?

$$pH = -\log[H_3O^+]$$

What is the pH of pure water at $25^{\circ}C$?

$$7.0$$

What is gravimetric analysis?

An analytical technique based on the measurement of mass.

What is a titration?

A volumetric technique that uses burets for the quantitative study of acid-base neutralization reactions.

What is the equivalence point in a titration?

The point in the titration where the acid has been neutralized.

What is an indicator?

A substance used to signal the equivalence point in a titration through a color change.

In a titration, what is the endpoint?

The point at which the indicator undergoes a color change.

What substance is frequently used to standardize $NaOH$ solutions?

The acid potassium hydrogen phthalate (KHP).