Module 5: Reactions in Aqueous Solutions

Practice flashcards covering definitions of solutions, electrolyte classifications, molarity calculations, dilutions, and solution stoichiometry from Module 5.

What is a solution, and what are its two essential components?

A solution is a homogeneous mixture of two or more pure substances consisting of a solvent (the substance present in the greatest amount) and one or more solutes (the substances dissolved in the solvent).

What is an aqueous solution, and how does the process of solvation occur?

An aqueous solution is a solution where water acts as the solvent; all substances dissolve by solvation, in which solvent particles surround solute particles.

According to the common types of solutions, what are the solute and solvent phases of club soda and brass?

Club soda is a liquid solution with a gas solute ($CO_2$) and a liquid solvent ($H_2O$). Brass is a solid solution with a solid solute and a solid solvent (copper and zinc alloys).

Why is water effective at dissolving both ionic compounds and polar substances?

Water has an uneven distribution of electrons that creates a partial negative charge (\text{\delta}^{-}) on the oxygen atom and a partial positive charge (\text{\delta}^{+}) on each hydrogen atom, enabling it to form electrostatic interactions with ions and polar molecules.

How does the dissolution of an ionic compound in water differ from that of a molecular compound such as sugar?

When an ionic compound dissolves, it dissociates into separate, independent ions ($\text{cations and anions}$). When a molecular compound dissolves, the molecules disperse into the solvent but remain intact as neutral molecules without dissociating.

What distinguishes an electrolyte solution from a nonelectrolyte solution in terms of conductivity?

An electrolyte solution contains dissolved ions that allow it to conduct electrical current, whereas a nonelectrolyte solution contains dissolved neutral molecules without ions and cannot conduct electricity.

Based on the electrolytic properties shown in the diagram, how do strong electrolytes, weak electrolytes, and nonelectrolytes behave at the molecular level?

Strong electrolytes dissolve completely as ions and conduct current well; weak electrolytes dissolve mostly as intact molecules with only a small fraction dissociating into ions, conducting current poorly; nonelectrolytes dissolve only as intact molecules without forming ions and do not conduct current.

Which seven acids are classified as strong acids that completely ionize in aqueous solution?

The seven strong acids are $HCl$, $HBr$, $HI$, $HClO_3$, $HClO_4$, $HNO_3$, and $H_2SO_4$.

What are the eight strong bases that completely dissociate into hydroxide ions in water?

The eight strong bases are $LiOH$, $NaOH$, $KOH$, $RbOH$, $CsOH$, $Ca(OH)_2$, $Sr(OH)_2$, and $Ba(OH)_2$.

Why is the ionization of weak acids and weak bases represented with equilibrium arrows ($\rightleftharpoons$)?

Because weak acids and bases only partially ionize in water, reaching a state of dynamic equilibrium where the rate of the forward ionization reaction equals the rate of the reverse reaction and the concentrations of species no longer change.

If 1 molecule/formula unit of each of $MgCl_2(s)$, $HNO_3(l)$, and $CH_3OH(l)$ is dissolved in water, how many ions will each form?

$MgCl_2(s)$ forms 3 ions ($Mg^{2+}$ and $2\,Cl^-$); $HNO_3(l)$ forms 2 ions ($H^+$ and $NO_3^-$); $CH_3OH(l)$ forms 0 ions because it is a molecular compound that dissolves without dissociating.

What is molarity ($M$), and what formula is used to calculate it?

Molarity is the concentration of a solution expressed as moles of solute per liter of solution: $M = \frac{\text{moles of solute (n)}}{\text{volume of solution in liters (V)}}$.

What steps are required to prepare a $1.00\,M\,NaCl$ solution using a volumetric flask as shown?

First, weigh out and add $1.00\,mol$ ($58.44\,g$) of $NaCl$ to the flask. Next, add water until the solid is dissolved, then continue adding water until reaching the $1\text{-liter mark}$. Finally, mix the solution thoroughly.

What volume (in $mL$) of a $0.40\,M\,NaOH$ solution is needed to obtain $0.020\,moles$ of $NaOH$?

$50.\,mL$, calculated using $V = \frac{n}{M} = \frac{0.020\,mol\,NaOH}{0.40\,M\,NaOH} = 0.050\,L = 50.\,mL$.

How many moles of solute are required to make $4.0\,L$ of a $1.5\,M$ solution?

$6.0\,mol$, calculated using $n = M \times V = (1.5\,mol/L)(4.0\,L) = 6.0\,mol$.

What is the molarity of a solution containing $25.5\,g$ of $KBr$ (molar mass = $119.00\,g/mol$) dissolved in enough water to make $1.75\,L$ of solution?

$0.122\,M$, calculated by dividing moles of $KBr$ ($25.5\,g / 119.00\,g/mol = 0.2143\,mol$) by $1.75\,L$.

What is the dilution equation, and why does $M_1 V_1 = M_2 V_2$ hold true?

The dilution equation is $M_1 V_1 = M_2 V_2$ (or $M_{con}V_{con} = M_{dil}V_{dil}$); the two sides are equal because dilution only adds solvent, meaning the total number of moles of solute ($M \times V$) remains unchanged.

To what volume should you dilute $0.020\,L$ of a $10.0\,M\,NaOH$ stock solution to obtain a $2.00\,M\,NaOH$ solution?

$0.100\,L$, calculated using $V_2 = \frac{M_1 V_1}{M_2} = \frac{(10.0\,mol/L)(0.020\,L)}{2.00\,mol/L} = 0.100\,L$.

How can $1.0\,L$ of $0.300\,M\,HCl$ be prepared from a $12\,M\,HCl$ stock solution?

Combine $25\,mL$ of $12\,M\,HCl$ with $975\,mL$ of water, calculated using $V_1 = \frac{M_2 V_2}{M_1} = \frac{(0.300\,M)(1.0\,L)}{12\,M} = 0.025\,L = 25\,mL$.

What general pathway is used in solution stoichiometry to determine the volume of Reactant B needed to react with a known volume of Reactant A as depicted in the diagram?

Convert the volume of reactant A to moles of A using the molarity of A; convert moles of A to moles of B using the stoichiometric mole ratio from the balanced equation; convert moles of B to volume of B using the molarity of B.

What is the molarity of an $H_2SO_4$ solution if $15.0\,mL$ of $0.200\,M\,NaOH$ is required to neutralize $20.0\,mL$ of the acid?

$0.075\,M$, calculated from $H_2SO_4 + 2 NaOH \rightarrow Na_2SO_4 + 2 H_2O$ where moles $NaOH = (0.0150\,L)(0.200\,M) = 0.00300\,mol$, yielding $0.00150\,mol\,H_2SO_4$, and $M = \frac{0.00150\,mol}{0.0200\,L} = 0.075\,M$.

What is the total concentration of phosphate ions in a $2.1\,M$ aqueous solution of magnesium phosphate ($Mg_3(PO_4)_2$)?

$4.2\,M$, because each formula unit of $Mg_3(PO_4)_2$ dissociates to yield 2 phosphate ions ($PO_4^{3-}$), making the ion concentration $2 \times 2.1\,M = 4.2\,M$.

When mixing $20.0\,mL$ of $0.400\,M\,Pb(NO_3)_2$ and $60.0\,mL$ of $0.200\,M\,NaI$, which reactant is limiting and what theoretical yield of $PbI_2$ precipitate forms?

$NaI$ is the limiting reactant because it produces only $0.00600\,mol$ of $PbI_2$ (compared to $0.00800\,mol$ from $Pb(NO_3)_2$), resulting in a theoretical yield of $2.77\,g\,PbI_2$ ($0.00600\,mol \times 461.00\,g/mol$).