CHEM1003 Chemistry Review: Acids, Bases, Equilibrium, Stoichiometry, and Intermolecular Forces

Flashcards covering chemical equilibrium, stoichiometry, solution concentration, acid-base chemistry, buffers, collision theory, and intermolecular forces based on CHEM1003 workshop materials.

What is the hydronium ion concentration $[H_3O^+]$ in a hydrochloric acid solution with a pH of $3.10$?

$$7.9 \times 10^{-4}\,\text{M}$$

Among boric acid ($Ka = 7.3 \times 10^{-10}$), acetic acid ($pKa = 4.75$), lactic acid ($Ka = 8.4 \times 10^{-4}$), and phenol ($pKa = 9.89$), which is the weakest acid?

Phenol is the weakest acid because it has the highest $pKa$ value ($9.89$).

Why is an acetic acid/acetate pair ($CH_3COOH/CH_3COO^-$) optimal for preparing a buffer solution at pH $4.8$?

Because the $pKa$ of acetic acid is $4.75$, which is closest to the target pH of $4.8$. Buffer capacity is highest when pH is close to $pKa$.

What is the pH of a $0.0035\,\text{M}$ $Ba(OH)_2$ aqueous solution?

pH = $11.85$. Since $Ba(OH)_2$ dissociates to give $[OH^-] = 2 \times 0.0035\,\text{M} = 0.007\,\text{M}$, $pOH = -\log(0.007) = 2.15$, making pH = $14 - 2.15 = 11.85$.

What is the molarity of a solution prepared by dissolving $25.0\,\text{g}$ of glucose ($C_6H_{12}O_6$) in water to a total volume of $500.0\,\text{mL}$?

$0.278\,\text{M}$. Moles of glucose = $\frac{25.0\,\text{g}}{180.16\,\text{g\,mol}^{-1}} = 0.139\,\text{mol}$, and molarity = $\frac{0.139\,\text{mol}}{0.5000\,\text{L}} = 0.278\,\text{M}$.

What volume of a $0.750\,\text{M}$ $HCl$ solution is required to prepare $250.0\,\text{mL}$ of $0.150\,\text{M}$ $HCl$?

$50.0\,\text{mL}$. Using $c_1 V_1 = c_2 V_2$, $V_1 = \frac{0.150\,\text{M} \times 250.0\,\text{mL}}{0.750\,\text{M}} = 50.0\,\text{mL}$.

What is the final concentration of $NaOH$ when $150.0\,\text{mL}$ of $0.200\,\text{M}$ $NaOH$ is mixed with $300.0\,\text{mL}$ of $0.150\,\text{M}$ $NaOH$?

$0.167\,\text{M}$. Total moles = $0.0300\,\text{mol} + 0.0450\,\text{mol} = 0.0750\,\text{mol}$ in a total volume of $0.4500\,\text{L}$.

What is the net ionic equation for the neutralization reaction between nitric acid ($HNO_3$) and potassium hydroxide ($KOH$)?

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

Which factor is NOT a requirement for an effective collision between reactant molecules?

The colliding molecules having different masses. The necessary factors are molecular collision, proper orientation, and sufficient energy to overcome the activation energy ($E_a$).

How does increasing temperature affect the equilibrium position of the exothermic reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) + \text{Heat}$?

It shifts the equilibrium position to the left (towards reactants), decreasing the amount of $NH_3$ at equilibrium.

What is the equilibrium constant expression $Kc$ for the reaction $P_4(s) + 6Cl_2(g) \rightleftharpoons 4PCl_3(l)$?

$Kc = \frac{1}{[Cl_2]^6}$, because pure solids ($P_4$) and pure liquids ($PCl_3$) are omitted from equilibrium expressions.

For the reaction $2NOCl(g) \rightleftharpoons 2NO(g) + Cl_2(g)$ ($Kc = 1.6 \times 10^{-5}$), in which direction will the reaction proceed if initial concentrations are $[NOCl] = 0.0120\,\text{M}$, $[NO] = 0.0050\,\text{M}$, and $[Cl_2] = 0.0030\,\text{M}$?

The reaction will proceed from right to left (towards reactants) to reach equilibrium.

If the equilibrium constant $Kc$ for $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$ is $64$ at $700\,\text{K}$, what is $Kc$ for the reverse reaction at the same temperature?

$0.0156$. The equilibrium constant for a reverse reaction is the reciprocal of the forward equilibrium constant ($Kc(\text{reverse}) = \frac{1}{64} \approx 0.0156$).

In the reaction $A \rightarrow B$, if the concentration of $A$ decreases from $0.500\,\text{M}$ to $0.300\,\text{M}$ in $20\,\text{minutes}$, what is the average reaction rate in $\text{M\,min}^{-1}$?

$0.0100\,\text{M\,min}^{-1}$. Calculated as $\text{Rate} = -\frac{\Delta [A]}{\Delta t} = -\frac{0.300\,\text{M} - 0.500\,\text{M}}{20\,\text{min}} = 0.0100\,\text{M\,min}^{-1}$.

For the balanced combustion of hexane $2C_6H_{14}(g) + 19O_2(g) \rightarrow 12CO_2(g) + 14H_2O(l)$, if the rate of hexane consumption is $1.20\,\text{mol\,L}^{-1}\,\text{s}^{-1}$, what is the rate of $O_2$ consumption?

$11.40\,\text{mol\,L}^{-1}\,\text{s}^{-1}$. Calculated as $1.20 \times \frac{19}{2} = 11.40\,\text{mol\,L}^{-1}\,\text{s}^{-1}$.

When $18.0\,\text{g}$ of $AgNO_3$ reacts with $22.4\,\text{g}$ of $FeCl_3$, what mass of $AgCl$ is formed and which reagent is limiting?

$AgNO_3$ is the limiting reagent, producing $15.2\,\text{g}$ of $AgCl$.

In the rocket fuel reaction $2N_2H_4(l) + N_2O_4(l) \rightarrow 3N_2(g) + 4H_2O(g)$, how many grams of $N_2$ gas are produced from $100\,\text{g}$ of $N_2H_4$ and $200\,\text{g}$ of $N_2O_4$?

$131\,\text{g}$ of $N_2$. Hydrazine ($N_2H_4$) is the limiting reagent ($3.12\,\text{mol}$), producing $4.68\,\text{mol}$ or $131\,\text{g}$ of $N_2$.

How does adding $NaOH$ affect the concentration of dichromate ions in the equilibrium $2CrO_4^{2-}(aq) + 2H^+(aq) \rightleftharpoons Cr_2O_7^{2-}(aq) + H_2O(l)$?

The concentration of dichromate ions ($Cr_2O_7^{2-}$) decreases. Hydroxide consumes $H^+$ ions, causing the equilibrium to shift to the left.

Which of the compounds $SF_4$, $CO_2$, $CH_3CH_2OH$, $HF$, $ICl_5$, and $XeF_4$ exhibit ONLY London dispersion forces?

$CO_2$ and $XeF_4$ exhibit only London dispersion forces because both are nonpolar molecules.

What are the dominant intermolecular forces in solid $CF_3(CF_2CF_2)_nCF_3$, solid $CO_2$, and solid $NaI$?

Solid $CF_3(CF_2CF_2)_nCF_3$ and solid $CO_2$ exhibit London dispersion forces; solid $NaI$ exhibits ionic forces.

Rank the compounds $CH_4$, $H_2S$, $H_2O$, and $MgO$ from lowest to highest melting point.

$CH_4 < H_2S < H_2O < MgO$ (London dispersion < dipole-dipole < hydrogen bonding < ionic forces).

Why does ethanoic acid exhibit stronger hydrogen bonding than propanol?

Ethanoic acid is a carboxylic acid, which allows for more extensive hydrogen bonding possibilities than an alcohol like propanol of similar size.

What type of intermolecular forces must be overcome when liquid hexane ($CH_3CH_2CH_2CH_2CH_2CH_3$) vaporizes?

London dispersion forces only, because hexane is nonpolar and covalent bonds within molecules remain intact during phase change.

What is the balanced equation for the reaction $NH_3(g) + O_2(g) \rightarrow NO(g) + H_2O(l)$?

$$4NH_3(g) + 5O_2(g) \rightarrow 4NO(g) + 6H_2O(l)$$

For a reaction with reactant enthalpy $201\,\text{kJ\,mol}^{-1}$, product enthalpy $259\,\text{kJ\,mol}^{-1}$, and activation energy $84\,\text{kJ\,mol}^{-1}$, what is the overall enthalpy change $\Delta H$ and energy level profile?

$\Delta H = +58\,\text{kJ\,mol}^{-1}$ ($259 - 201 = +58\,\text{kJ\,mol}^{-1}$), indicating an endothermic reaction.