Chapter 4: Chemical Reactions in Aqueous Solutions

Flashcards covering chemical reactions in aqueous solutions, molarity, dilutions, electrolytes, stoichiometry, precipitation rules, net ionic equations, titrations, and balancing redox reactions.

How are solute and solvent defined when forming a homogeneous solution?

The component of the solution that changes state is called the solute, while the component that keeps its state is called the solvent. If both components start in the same state, the major component is the solvent.

What is an aqueous solution?

An aqueous solution is a solution in which water acts as the solvent.

What is molarity ($M$) and what is its formula?

Molarity is the solution concentration expressed as moles of solute per $1\,\text{liter}$ of solution. Its formula is: $\text{molarity, } M = \frac{\text{amount of solute (in moles)}}{\text{amount of solution (in L)}}$

What are the laboratory steps required to prepare $1.00\,\text{L}$ of a $1.00\,M\,\text{NaCl}$ solution as shown in this diagram?

Weigh out and add $1.00\,\text{mol}$ of $\text{NaCl}$ ($58.44\,\text{g}$) into a flask, add water until the solid is dissolved, and then add additional water until the $1\text{-liter}$ mark is reached and mix.

What is the molarity of a solution made by dissolving $25.5\,\text{g}$ of $\text{KBr}$ ($1\,\text{mol KBr} = 119.00\,\text{g}$) in $1.75\,\text{L}$ of solution?

$$0.122\,M$$

What is the dilution formula, and why does the amount of solute remain constant during dilution?

The dilution formula is $M_1 V_1 = M_2 V_2$. It holds because adding more solvent increases the total volume of solution without changing the amount of solute ($\text{moles solute in solution 1} = \text{moles solute in solution 2}$).

To what volume should you dilute $0.200\,\text{L}$ of $15.0\,M\,\text{NaOH}$ to make a $3.00\,M\,\text{NaOH}$ solution?

$$1.00\,\text{L}$$

What volume of $0.150\,M\,\text{KCl}$ is required to completely react with $0.150\,\text{L}$ of $0.175\,M\,\text{Pb(NO}_3\text{)}_2$ in the reaction $2\,\text{KCl}(aq) + \text{Pb(NO}_3\text{)}_2(aq) \rightarrow \text{PbCl}_2(s) + 2\,\text{KNO}_3(aq)$?

$$0.350\,\text{L}$$

Based on the conductivity testing apparatus pictured, how do electrolytes and nonelectrolytes differ when dissolved in water?

Electrolytes dissolve in water to form solutions that conduct electricity (lighting the bulb), whereas nonelectrolytes dissolve in water to form solutions that do not conduct electricity.

How do ionic compounds and molecular compounds differ when they dissolve in water?

Ionic compounds dissociate into ions when dissolved, so the compound itself no longer exists in solution. Molecular compounds do not dissociate when they dissolve, so the compound molecules themselves exist in solution.

How do strong electrolytes and weak electrolytes differ in dissociation and electrical conductivity?

Strong electrolytes (such as ionic compounds and strong acids) dissolve completely as ions and conduct electricity well. Weak electrolytes (such as weak acids) dissolve mostly as molecules and only partially as ions, conducting electricity poorly.

What examples are given for weak acids, weak bases, and nonelectrolytes?

Weak acid: acetic acid ($\text{HC}_2\text{H}_3\text{O}_2$); Weak base: $\text{NH}_3$; Nonelectrolytes: ethanol ($\text{C}_2\text{H}_5\text{OH}$) and sucrose ($\text{C}_{12}\text{H}_{22}\text{O}_{11}$).

If $6.37\,\text{g}$ of $\text{Al(NO}_3\text{)}_3$ (molar mass = $213.0\,\text{g\,mol}^{-1}$) is dissolved in water to make $250\,\text{mL}$ of solution, what are the concentrations of $\text{Al}^{3+}$ and $\text{NO}_3^-$ ions?

$[\text{Al}^{3+}] = 0.120\,M$ and $[\text{NO}_3^-] = 0.360\,M$ (while the molarity of intact $\text{Al(NO}_3\text{)}_3$ molecule is $0\,M$).

What are the three main types of chemical reactions in aqueous solution?

Precipitation reactions, acid-base reactions, and reduction-oxidation (redox) reactions.

What is a precipitation reaction and what is a precipitate, as shown in this reaction between $\text{KI}(aq)$ and $\text{Pb(NO}_3\text{)}_2(aq)$?

A precipitation reaction is a reaction between aqueous solutions of ionic compounds that produces an insoluble ionic compound in water. The insoluble product is called a precipitate (here, solid $\text{PbI}_2$).

Why is there no reaction when mixing $\text{KI}(aq)$ and $\text{NaCl}(aq)$?

Because both potential ionic products ($\text{KCl}$ and $\text{NaI}$) are soluble in water, no precipitate forms and all ions remain present in solution.

Which ions form compounds that are generally soluble in water with no exceptions according to solubility rules?

Compounds containing $\text{Li}^+$, $\text{Na}^+$, $\text{K}^+$, $\text{NH}_4^+$, $\text{NO}_3^-$, $\text{C}_2\text{H}_3\text{O}_2^-$, and $\text{F}^-$.

According to solubility rules, what are the insoluble exceptions for compounds containing halides ($\text{Cl}^-$, $\text{Br}^-$, $\text{I}^-$) and sulfates/carbonates ($\text{SO}_4^{2-}$, $\text{CO}_3^{2-}$)?

For halides ($\text{Cl}^-$, $\text{Br}^-$, $\text{I}^-$), exceptions are $\text{Ag}^+$, $\text{Hg}_2^{2+}$, and $\text{Pb}^{2+}$. For $\text{SO}_4^{2-}$ and $\text{CO}_3^{2-}$, exceptions are $\text{Ag}^+$, $\text{Ca}^{2+}$, $\text{Sr}^{2+}$, $\text{Ba}^{2+}$, and $\text{Pb}^{2+}$.

How do molecular equations, complete ionic equations, and net ionic equations differ?

Molecular equations write reactants and products as neutral formula units. Complete ionic equations write all dissolved strong electrolytes as separated ions. Net ionic equations remove spectator ions (ions appearing on both sides) to show only species participating in the reaction.

What is the net ionic equation for all acid-base neutralization reactions forming a soluble salt?

$$\text{H}^+(aq) + \text{OH}^-(aq) \rightarrow \text{H}_2\text{O}(l)$$

Define titrant, analyte, equivalence point, and indicator in an acid-base titration visual.

Titrant is the solution of known concentration; analyte is the solution of unknown concentration; equivalence point is when $\text{H}^+$ and $\text{OH}^-$ are in their stoichiometric ratio and completely reacted; indicator is a dye whose color changes based on solution acidity or basicity.

A $10.0\,\text{mL}$ sample of $0.20\,M\,\text{HBr}$ solution is titrated with $0.10\,M\,\text{NaOH}$. What volume of $\text{NaOH}$ is required to reach the equivalence point?

$$20.0\,\text{mL}$$

How are oxidation and reduction defined in terms of oxygen transfer and electron transfer?

In oxygen transfer, oxidation is adding oxygen to an element/compound and reduction is removing oxygen (reducing ore to metal). In electron transfer, oxidation is the loss of electrons and reduction is the gain of electrons.

According to Table 4.2, what are the general rules for assigning oxidation states to elements, monatomic ions, fluorine, oxygen, and hydrogen?

An atom in a free element is $0$; a monatomic ion equals its charge; Fluorine is $-1$ in its compounds; Oxygen is usually $-2$ (except in peroxides containing $\text{O}_2^{2-}$ where it is $-1$); Hydrogen is $+1$ in covalent compounds.

What is a combustion reaction, and what is the sequence for balancing it?

A combustion reaction is a subclass of redox reactions in which $\text{O}_2(g)$ is a reactant, releasing energy. To balance: 1. Balance carbon, 2. Balance hydrogen, 3. Balance oxygen (if an odd number of oxygen atoms is needed as a coefficient, multiply the entire equation by $2$).

What are the balanced equations for the combustion of $\text{C}_3\text{H}_7\text{OH}(l)$ and $\text{CH}_3\text{NH}_2(g)$?

$2\,\text{C}_3\text{H}_7\text{OH}(l) + 9\,\text{O}_2(g) \rightarrow 6\,\text{CO}_2(g) + 8\,\text{H}_2\text{O}(g)$ and $4\,\text{CH}_3\text{NH}_2(g) + 13\,\text{O}_2(g) \rightarrow 4\,\text{CO}_2(g) + 10\,\text{H}_2\text{O}(g) + 4\,\text{NO}_2(g)$

What is the balanced net redox reaction for $\text{Cr}_2\text{O}_7^{2-}(aq) + \text{SO}_3^{2-}(aq) \rightarrow \text{Cr}^{3+}(aq) + \text{SO}_4^{2-}(aq)$ in acidic solution?

$$\text{Cr}_2\text{O}_7^{2-}(aq) + 3\,\text{SO}_3^{2-}(aq) + 8\,\text{H}^+(aq) \rightarrow 2\,\text{Cr}^{3+}(aq) + 3\,\text{SO}_4^{2-}(aq) + 4\,\text{H}_2\text{O}(l)$$

What steps are added to the half-reaction method when balancing a redox reaction in basic solution?

1. Balance as in acid. 2. Add $\text{OH}^-$ equal to $\text{H}^+$ ions to both sides. 3. Form water by combining $\text{H}^+$ and $\text{OH}^-$. 4. Check elements and charges for balance.