Stoichiometry practice questions

Question 1

A student heats a sample of pure titanium metal, $\text{Ti}$, in a crucible with excess oxygen until the metal is completely converted to titanium oxide. The student records the mass measurements in the table below.

| Measurement | Mass (g) |
|---|---|
| Mass of empty crucible and lid | 15.00 |
| Mass of crucible, lid, and $\text{Ti}$ sample | 17.40 |
| Mass of crucible, lid, and titanium oxide | 19.00 |

Based on the data in the table, what is the empirical formula of the titanium oxide?

Accepted Answer

$\text{TiO}_2$

Answer

$\text{TiO}$

Answer

$\text{Ti}_2\text{O}$

Answer

$\text{Ti}_2\text{O}_3$

Question 2

A student performs a gravimetric analysis experiment to determine the mass percent of $\text{Cl}$ in an unknown soluble salt mixture. The student dissolves a $0.500 \text{ g}$ sample of the mixture in distilled water and adds an excess of $\text{AgNO}_3\text{(aq)}$ to precipitate $\text{AgCl(s)}$. The precipitate is collected by filtration and weighed. Which of the following experimental errors would cause the calculated mass percent of $\text{Cl}$ in the mixture to be higher than the actual mass percent?

Accepted Answer

Failing to completely dry the $\text{AgCl(s)}$ precipitate before measuring its final mass

Answer

Adding an insufficient volume of $\text{AgNO}_3\text{(aq)}$, leaving some $\text{Cl}^-\text{(aq)}$ unreacted in solution

Answer

Spilling a small portion of the solution containing the dissolved salt mixture before adding $\text{AgNO}_3\text{(aq)}$

Answer

Rinsing the $\text{AgCl(s)}$ precipitate with distilled water while it is on the filter paper prior to drying

Question 3

The decomposition of ozone, $\text{O}_3\text{(g)}$, is proposed to occur through the following two-step mechanism:

Step 1: $\text{O}_3\text{(g)} \rightleftharpoons \text{O}_2\text{(g)} + \text{O(g)}$
Step 2: $\text{O}_3\text{(g)} + \text{O(g)} \rightarrow 2\,\text{O}_2\text{(g)}$

Which of the following represents the overall balanced chemical equation for the reaction?

Accepted Answer

$2\,\text{O}_3\text{(g)} \rightarrow 3\,\text{O}_2\text{(g)}$

Answer

$2\,\text{O}_3\text{(g)} + \text{O(g)} \rightarrow 3\,\text{O}_2\text{(g)} + \text{O(g)}$

Answer

$\text{O}_3\text{(g)} + \text{O(g)} \rightarrow 2\,\text{O}_2\text{(g)}$

Answer

$\text{O}_3\text{(g)} \rightarrow \text{O}_2\text{(g)} + \text{O(g)}$

Question 4

A student titrates a $20.00 \text{ mL}$ sample of an $\text{HCl(aq)}$ solution of unknown concentration with a standardized $0.100 \text{ M NaOH(aq)}$ solution using phenolphthalein as an indicator. The student records the buret readings for three trials in the table below.

| Trial | Volume of $\text{HCl(aq)}$ ($\text{mL}$) | Initial buret reading ($\text{mL}$) | Final buret reading ($\text{mL}$) |
|-------|-------------------------------------------|--------------------------------------|------------------------------------|
| 1     | 20.00                                     | 0.50                                 | 10.50                              |
| 2     | 20.00                                     | 10.50                                | 20.50                              |
| 3     | 20.00                                     | 20.50                                | 30.50                              |

Based on the titration data, what is the molar concentration of the $\text{HCl(aq)}$ solution?

Accepted Answer

$0.0500 \text{ M}$

Answer

$0.100 \text{ M}$

Answer

$0.200 \text{ M}$

Answer

$0.400 \text{ M}$

Question 5

A student performs an experiment by adding solid sodium hydrogen carbonate, $\text{NaHCO}_3(s)$, to an aqueous solution of acetic acid, $\text{CH}_3\text{COOH}(aq)$. The student observes rapid formation of gas bubbles, and the temperature of the mixture decreases. Which of the following correctly classifies this process and identifies the primary particulate-level interactions involved?

Accepted Answer

| Classification | Primary Particulate-Level Interactions ||---|---|| Chemical change | Intramolecular chemical bonds broken and formed |

Answer

| Classification | Primary Particulate-Level Interactions ||---|---|| Physical change | Intermolecular forces overcome |

Answer

| Classification | Primary Particulate-Level Interactions ||---|---|| Physical change | Intramolecular chemical bonds broken and formed |

Answer

| Classification | Primary Particulate-Level Interactions ||---|---|| Chemical change | Intermolecular forces overcome |

Question 6

A student observes the particulate representations below, representing a pure substance $X$ undergoing a physical change in a sealed, rigid container of constant volume. Which of the following correctly compares the particle density and translational mobility of substance $X$ in Box $2$ relative to Box $1$?

Accepted Answer

In Box $2$, the particle density is lower and the translational mobility of the particles is greater than in Box $1$.

Answer

In Box $2$, the particle density is higher and the translational mobility of the particles is greater than in Box $1$.

Answer

In Box $2$, the particle density is lower and the translational mobility of the particles is smaller than in Box $1$.

Answer

In Box $2$, the particle density is higher and the translational mobility of the particles is smaller than in Box $1$.

Question 7

A 1.50 g sample of a pure organic compound containing only carbon, hydrogen, and oxygen is completely burned in excess oxygen gas. All of the carbon in the compound is converted to $\text{CO}_2\text{(g)}$ and all of the hydrogen is converted to $\text{H}_2\text{O(g)}$. The masses of the products collected are shown in the table below.

| Product | Mass (g) |
|---|---|
| $\text{CO}_2\text{(g)}$ | 2.20 |
| $\text{H}_2\text{O(g)}$ | 0.90 |

Based on these data, what is the empirical formula of the compound?

Accepted Answer

$\text{CH}_2\text{O}$

Answer

$\text{C}_2\text{H}_4\text{O}$

Answer

$\text{CH}_4\text{O}$

Answer

$\text{C}_2\text{H}_2\text{O}_3$

Question 8

A student investigates the gas-phase decomposition of dinitrogen pentoxide at a constant temperature in a rigid container, as represented by the balanced equation below:

$2\text{N}_2\text{O}_5\text{(g)} \rightarrow 4\text{NO}_2\text{(g)} + \text{O}_2\text{(g)}$

At a particular instant during the reaction, the student measures the rate of concentration change for each species. Which of the following correctly ranks the absolute rates of concentration change, $\left|\dfrac{\Delta[\text{X}]}{\Delta t}\right|$, for the three gases at this instant, from greatest to least?

Accepted Answer

$\left|\dfrac{\Delta[\text{NO}_2]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{N}_2\text{O}_5]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{O}_2]}{\Delta t}\right|$

Answer

$\left|\dfrac{\Delta[\text{O}_2]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{N}_2\text{O}_5]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{NO}_2]}{\Delta t}\right|$

Answer

$\left|\dfrac{\Delta[\text{NO}_2]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{O}_2]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{N}_2\text{O}_5]}{\Delta t}\right|$

Answer

$\left|\dfrac{\Delta[\text{N}_2\text{O}_5]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{NO}_2]}{\Delta t}\right| > \left|\dfrac{\Delta[\text{O}_2]}{\Delta t}\right|$

Question 9

A student mixes $100.0 \text{ mL}$ of $0.200 \text{ M } \text{Pb(NO}_3)_2\text{(aq)}$ with $100.0 \text{ mL}$ of $0.300 \text{ M } \text{KI(aq)}$, resulting in the formation of a yellow precipitate according to the balanced net ionic equation below.

$$\text{Pb}^{2+}\text{(aq)} + 2\,\text{I}^-\text{(aq)} \rightarrow \text{PbI}_2\text{(s)}$$

Assuming the reaction goes to completion, how many moles of the excess reactant remain unreacted?

Accepted Answer

$0.0050 \text{ mol}$

Answer

$0.0100 \text{ mol}$

Answer

$0.0150 \text{ mol}$

Answer

$0.0200 \text{ mol}$

Question 10

The particulate diagrams above represent the contents of a rigid, closed container before and after a reaction between $\text{CO(g)}$ and $\text{O}_2\text{(g)}$ occurs to produce $\text{CO}_2\text{(g)}$. Based on the diagrams, which of the following statements correctly identifies the limiting reactant and provides the correct justification?

Accepted Answer

$\text{CO(g)}$ is the limiting reactant because all 6 molecules of $\text{CO(g)}$ are completely consumed to form 6 molecules of $\text{CO}_2\text{(g)}$, leaving 1 unreacted molecule of $\text{O}_2\text{(g)}$.

Answer

$\text{O}_2\text{(g)}$ is the limiting reactant because it has a smaller stoichiometric coefficient than $\text{CO(g)}$ in the balanced chemical equation $2\,\text{CO(g)} + \text{O}_2\text{(g)} \rightarrow 2\,\text{CO}_2\text{(g)}$.

Answer

$\text{CO(g)}$ is the limiting reactant because it reacts with $\text{O}_2\text{(g)}$ in a 1:1 mole ratio, consuming 4 molecules of $\text{CO(g)}$ and 4 molecules of $\text{O}_2\text{(g)}$.

Answer

$\text{O}_2\text{(g)}$ is the limiting reactant because there are fewer molecules of $\text{O}_2\text{(g)}$ (4 molecules) than $\text{CO(g)}$ (6 molecules) in the initial mixture.

Question 11

A student combines $100.0 \, \text{mL}$ of $0.10 \, \text{M} \, \text{Pb(NO}_3\text{)}_2(\text{aq})$ with $100.0 \, \text{mL}$ of $0.10 \, \text{M} \, \text{KI}(\text{aq})$ at $25^\circ\text{C}$, causing a yellow precipitate of $\text{PbI}_2(\text{s})$ to form. Which of the following predictions correctly ranks the molar concentrations of the ions remaining in the solution from highest to lowest after the reaction goes to completion?

Accepted Answer

$[\text{NO}_3^-] > [\text{K}^+] > [\text{Pb}^{2+}] > [\text{I}^-]$

Answer

$[\text{NO}_3^-] > [\text{K}^+] = [\text{Pb}^{2+}] > [\text{I}^-]$

Answer

$[\text{NO}_3^-] > [\text{Pb}^{2+}] > [\text{K}^+] > [\text{I}^-]$

Answer

$[\text{K}^+] > [\text{NO}_3^-] > [\text{Pb}^{2+}] > [\text{I}^-]$

Question 12

A student conducts a reaction to synthesize ammonia gas according to the balanced equation below.

$$\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightarrow 2\text{NH}_3\text{(g)}$$

The student combines $56 \text{ g}$ of $\text{N}_2\text{(g)}$ and $9.0 \text{ g}$ of $\text{H}_2\text{(g)}$ in a closed reaction vessel and allows the reaction to proceed to completion. Assuming a 100% yield, what is the theoretical yield of $\text{NH}_3\text{(g)}$ produced?

Accepted Answer

$51 \text{ g}$

Answer

$26 \text{ g}$

Answer

$34 \text{ g}$

Answer

$68 \text{ g}$

Question 13

A student heats a pure limestone sample in a model kiln. The CaCO decomposition occurs according to the equation

$\text{CaCO}_3\text{(s)} \rightarrow \text{CaO(s)} + \text{CO}_2\text{(g)}$

The student completely decomposes $25.0\text{ g}$ of $\text{CaCO}_3$. The molar mass of $\text{CaCO}_3$ is $100.\text{ g/mol}$, and one mole of gas occupies $22.4\text{ L}$ at standard temperature and pressure. What volume of $\text{CO}_2\text{(g)}$ is produced at standard temperature and pressure?

Accepted Answer

$5.60\text{ L}$

Answer

$0.0112\text{ L}$

Answer

$0.560\text{ L}$

Answer

$2.80\text{ L}$

Question 14

A student adds a piece of solid zinc to an aqueous solution of hydrochloric acid, as represented by the balanced equation below:

$$\text{Zn}(s) + 2\text{HCl}(aq) \rightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)$$

Which of the following best predicts and justifies the sign of the standard entropy change, $\Delta S^\circ$, for this reaction?

Accepted Answer

$\Delta S^\circ > 0$, because a gas is produced from solid and aqueous reactants, leading to a net increase in matter dispersal.

Answer

$\Delta S^\circ > 0$, because the reaction is exothermic and transfers heat energy to the surroundings.

Answer

$\Delta S^\circ < 0$, because the total number of moles of products is less than the total number of moles of reactants.

Answer

$\Delta S^\circ < 0$, because the formation of aqueous zinc ions restricts the motion of surrounding water molecules.

Question 15

Two metal blocks, $\text{Block X}$ and $\text{Block Y}$, are brought into contact inside an insulated container. The initial particulate state of the two blocks is shown in the diagram, where the length of each arrow represents the relative speed of a particle. Which of the following best describes the system after thermal equilibrium is reached?

Accepted Answer

Energy has transferred as heat from $\text{Block X}$ to $\text{Block Y}$, and the average kinetic energy of the particles in $\text{Block X}$ is equal to the average kinetic energy of the particles in $\text{Block Y}$.

Answer

Energy has transferred as heat from $\text{Block Y}$ to $\text{Block X}$, and the average kinetic energy of the particles in $\text{Block X}$ remains greater than that of $\text{Block Y}$.

Answer

Energy has transferred as heat from $\text{Block X}$ to $\text{Block Y}$, and all molecular motion in both blocks has ceased.

Answer

Energy has transferred as heat from $\text{Block X}$ to $\text{Block Y}$ until all particles in $\text{Block X}$ have lower kinetic energy than all particles in $\text{Block Y}$.

Question 16

The synthesis of ammonia is represented by the following balanced equation:

$\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightarrow 2\text{NH}_3\text{(g)}$

Which of the following best predicts the sign of the standard entropy change, $\Delta S^\circ$, for the reaction and provides the correct justification?

Accepted Answer

$\Delta S^\circ < 0$, because the reaction results in a net decrease in the number of moles of gas.

Answer

$\Delta S^\circ < 0$, because energy is released as new chemical bonds form in the products.

Answer

$\Delta S^\circ > 0$, because two different element species combine to form a compound with greater structural complexity.

Answer

$\Delta S^\circ > 0$, because the total mass and total number of atoms are conserved during the reaction.

Question 17

A student mixes aqueous sodium carbonate, $\text{Na}_2\text{CO}_3\text{(aq)}$, with excess aqueous hydrochloric acid, $\text{HCl(aq)}$, and observes vigorous bubbling due to the evolution of a gas. Which of the following is the correct balanced chemical equation for the overall reaction?

Accepted Answer

$\text{Na}_2\text{CO}_3\text{(aq)} + 2\text{HCl(aq)} \rightarrow 2\text{NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$

Answer

$\text{Na}_2\text{CO}_3\text{(aq)} + \text{HCl(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$

Answer

$\text{Na}_2\text{CO}_3\text{(aq)} + 2\text{HCl(aq)} \rightarrow 2\text{NaCl(aq)} + \text{H}_2\text{CO}_3\text{(aq)}$

Answer

$\text{Na}_2\text{CO}_3\text{(aq)} + 2\text{HCl(aq)} \rightarrow 2\text{NaCl(aq)} + \text{H}_2\text{(g)} + \text{CO}_3\text{(g)}$

Question 18

A student prepares an aqueous solution of a weak monoprotic acid, $\text{HA(aq)}$. The particulate diagram below represents a sample of the solution after chemical equilibrium is established. Water molecules are omitted for clarity.

Based on the representation, what is the percent ionization of $\text{HA}$ in this solution?

Accepted Answer

$20\%$

Answer

$25\%$

Answer

$80\%$

Answer

$100\%$

Stoichiometry Multiple Choice Questions & Quizzes

Where This Topic Shows Up

Find More Questions On Related Topics

Practice Questions

Quizzes