Practice Test 12 - High School Chemistry

20 questions. Answer them in any order, then submit to see your score and every explanation.

Propane combusts according to the balanced equation $\mathrm{C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O}$ . What is the mole ratio of $\mathrm{CO_2}$ produced to $\mathrm{C_3H_8}$ consumed?
Element X has electron configuration $[Ne]3s^1$ and element Y has electron configuration $[Ne]3s^2\,3p^5$ . The first ionization energy of Y is higher than that of X. Which explanation best accounts for this difference using electron configuration ideas?
A single concentration-versus-time curve for reactant $D$ is shown. The curve is steeply decreasing at early times and is nearly horizontal at late times. At which part of the graph is the reaction rate closest to zero? Axes: y = concentration of $[D]$ (arbitrary units), x = time (s).
A student heats sugar in a dry test tube and observes it turns brown. Another student argues it is only a physical change (like melting). Your teacher asks you to design an investigation to determine whether heating sugar produces a chemical change. Which design best uses measurable evidence to answer the question safely?
A class tested two materials for disposable gloves to handle a dilute bleach solution (sodium hypochlorite). Material A (thin vinyl) showed no visible damage after 20 minutes but tore easily during use. Material B (nitrile) did not tear but became slightly stiff and showed faint discoloration after 20 minutes. The task requires 15-minute handling with good dexterity and low failure risk. Which refinement best balances the evidence from both tests?
A spacecraft uses a radioisotope battery (powered by radioactive decay, a nuclear process) and can operate for decades. A phone uses a lithium-ion battery (a chemical process) and typically lasts about a day between charges. Which explanation best connects these examples to energy scale?
Hydrogen chloride forms by $\text{H}_2 + \text{Cl}_2 \rightarrow 2\text{HCl}.$ If $5.0\ \text{mol}$ of $\text{H}_2$ and $2.0\ \text{mol}$ of $\text{Cl}_2$ are mixed, which reactant will be completely consumed first?
A student claims: "Increasing the concentration of hydrochloric acid (HCl) increases the reaction rate with magnesium." The student measures the time for a 2.0 cm strip of magnesium ribbon to completely stop bubbling in HCl at 25°C. Evidence (three trials each): - 0.50 M HCl: 78 s, 81 s, 79 s - 1.00 M HCl: 41 s, 39 s, 40 s - 1.50 M HCl: 28 s, 30 s, 29 s - The magnesium ribbon looked shiny before each trial. Do the data support the claim?
A disposable hand warmer contains iron powder that reacts with oxygen when exposed to air. After shaking it, the temperature increases from 20°C to 45°C over several minutes without any external heating. What does this indicate about the reaction?
Two processes are described: - Process X: atoms rearrange electrons to break and form chemical bonds (combustion, batteries, metabolism). - Process Y: the nucleus changes (fission in power plants, fusion in the Sun, radioactive decay). Which comparison is most accurate about the typical energy scale per event for Process X vs Process Y?
A student repeated the same titration endpoint measurement three times using the same solutions and procedure. The student recorded the volume of NaOH needed to reach the phenolphthalein endpoint. Which conclusion about data collection quality is best supported by the results?
A student reacts 2.0 g of calcium carbonate (CaCO $_3$ ) with the same volume and concentration of acid at the same temperature. Only the form of CaCO $_3$ changes. Condition 1: large chips → fizzing lasts ~120 s Condition 2: small chips → fizzing lasts ~40 s Condition 3: powder → fizzing lasts ~10 s Which statement best explains why the powder reacts fastest?
A community garden wants labels for plant pots that will last all season. The labels will be outdoors in sun and rain, and they may be splashed with fertilizer solution and occasional pesticide spray. The writing must remain readable and the label should not break down into harmful chemicals in the soil. Which set of chemical properties best fits this application?
A school lab designed a container for storing dilute hydrochloric acid (0.5 M). Their initial container used a steel screw cap with a rubber gasket on a glass bottle because it sealed tightly. After 3 months: - The steel cap showed rust and pitting on the inside surface. - The rubber gasket became brittle and cracked. - The glass bottle itself remained unchanged. Which refinement best targets the chemical compatibility problems shown?
A single-step reaction energy diagram has reactants at 50 kJ, a peak at 120 kJ, and products at 30 kJ (energy on y-axis, reaction progress on x-axis). Which vertical difference represents the activation energy $E_a$ ?
Water forms by: $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ If $8.0\,\text{mol}$ of $\text{H}_2$ reacts with $3.0\,\text{mol}$ of $\text{O}_2$ , which statement is correct?
A student reacts magnesium ribbon with hydrochloric acid in a beaker: $\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$ At 22°C, 1.0 M HCl, and the same length of magnesium ribbon, the bubbling of $\text{H}_2$ gas is moderate. The student proposes warming the acid to 35°C while keeping the acid concentration and magnesium ribbon the same. How will the reaction rate change, and why (collision theory)?
Magnesium (Mg) has electron configuration $[Ne]3s^2$ and chlorine (Cl) has electron configuration $[Ne]3s^2\,3p^5$ . Both are in period 3, and chlorine has a smaller atomic radius than magnesium. Which explanation best connects their electron configurations to this size difference?
A student heats a sample of calcium carbonate strongly. The reaction (thermal decomposition) only continues while the burner is on and stops when heating is removed. Which classification best fits this reaction based on the need for continuous energy input?
A town is considering building a nuclear fission power plant to replace an aging coal plant. Supporters note that nuclear plants generate large amounts of electricity reliably and produce very low greenhouse gas emissions during operation. Opponents worry about the possibility of a serious accident releasing radiation, the challenge of storing high-level radioactive waste for thousands of years, and the need for strong security to prevent misuse of nuclear materials. Which statement best shows a balanced evaluation of this proposal?

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