Practice Test 4 - High School Chemistry

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

Students ask: How does the surface area of calcium carbonate affect the rate of reaction with hydrochloric acid? They prepare three samples of calcium carbonate: powder, small chips, and large chunks. For each trial, they measure 5.00 g of the calcium carbonate sample and add it to 50.0 mL of 1.0 M HCl in an identical flask at room temperature (about 22°C). Immediately after adding the solid, they start a timer and count the number of gas bubbles produced in the first 30 seconds. Which list best describes controlled variables that should be kept the same across trials for a fair test?
Oxygen has atomic number 8. What is the electron configuration of the oxide ion, O²⁻?
Consider the balanced equation: $\mathrm{2H_2 + O_2 \rightarrow 2H_2O}$ If $5.0\ \text{mol}$ of $\mathrm{H_2}$ react completely, how many moles of $\mathrm{H_2O}$ form?
Magnesium (Mg) is in group 2 and has 2 valence electrons (electron configuration ends in 3s²). Magnesium commonly forms Mg²⁺ in ionic compounds such as MgCl₂. Why does magnesium form a 2+ ion?
Some foods are irradiated to kill bacteria and parasites and to extend shelf life without adding chemical preservatives. The process uses controlled radiation sources and is regulated. A concern is that facilities must prevent worker exposure and securely manage radioactive sources. Which statement best reflects a balanced understanding of this technology?
A manufacturer redesigned a household drain cleaner bottle. The original cap was made of aluminum, but some customers reported the cap becoming difficult to open after repeated use. The product contains sodium hydroxide (a strong base). The new design uses a polypropylene (PP) cap. In a 3-month shelf test, aluminum caps showed surface dulling and occasional sticking, while PP caps showed no visible change. Which justification best supports the switch to PP?
A reaction between two dissolved reactants is carried out in a beaker at $20^\circ\text{C}$ . The student wants the reaction to go faster but is only allowed to change one condition. The reactants are already fully dissolved, and no solid is present. Which single change would most reliably increase the reaction rate based on collision theory?
Two product curves, X and Y, are shown on a concentration-versus-time graph. Curve X rises steeply at first and reaches a plateau sooner than Curve Y, which rises more gradually. Which statement is best supported by the graph?
Two reactions are listed below: Reaction A: $\Delta H = -200\ \text{kJ}$ Reaction B: $\Delta H = +200\ \text{kJ}$ Which statement correctly compares the energy changes involved?
Use the periodic trend for first ionization energy. Arrange these period 2 elements in order of decreasing first ionization energy: - Li (group 1) - N (group 15) - Ne (group 18)
Which product nucleus forms in the beta decay $^{14}_{6}\text{C} \rightarrow \text{(product)} + ^{0}_{-1}\text{e}?$
A hospital is expanding its cancer center and plans to add radiation therapy for tumors. Doctors explain that carefully targeted radiation can kill cancer cells and save lives, but it also exposes nearby healthy tissue to radiation, which can cause side effects and slightly increase the risk of later health problems. Which choice best balances the benefits and risks of using radiation therapy?
A student adds 1.00 g of magnesium ribbon to 25 mL of clear vinegar (aqueous acetic acid) in a beaker. The beaker is left uncovered on the lab bench for 10 minutes. Observations and measurements: - Immediately after adding Mg: many small bubbles form on the metal surface. - After 10 minutes: most of the Mg ribbon is gone; a small piece remains. - Temperature changes from 22.0°C to 28.5°C. - The liquid remains colorless and clear (no cloudiness). - When a burning splint is held near the mouth of the beaker, a brief "pop" sound is heard. Did a chemical reaction occur? Choose the justification that best supports your conclusion using claim-evidence-reasoning (CER).
A student argues: "If you burn enough gasoline, you can match the energy from a nuclear power plant, so chemical reactions must release the same energy per atom as nuclear reactions." Which response best addresses the mistake?
Sodium has electron configuration [Ne]3s1 and chlorine has electron configuration [Ne]3s2 3p5. Both are in period 3. Chlorine has a smaller atomic radius than sodium. Which electron-configuration-based explanation best accounts for this trend?
A company is choosing a material for reusable water bottles. Requirements: (1) must be non-toxic and not add taste/odor, (2) should survive drops, (3) should tolerate hot water washing (not boiling), and (4) moderate cost (not luxury). Which option best balances the trade-offs? Materials: - Stainless steel: very durable; doesn't shatter; generally inert with water; but higher cost and opaque. - Polycarbonate plastic: light and cheap; tough; but can scratch and may retain odors; some versions have safety concerns depending on additives. - Glass: very inert and no taste; but breaks when dropped and is heavier.
Calcium carbonate decomposes as $\mathrm{CaCO_3 \rightarrow CaO + CO_2}.$ Which mole ratio statement is correct for $\mathrm{CaCO_3}$ to $\mathrm{CO_2}$ ?
In a sealed container, 10 g of carbon reacts completely with 30 g of oxygen to form carbon dioxide: $\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)$ After the reaction, what should be the total mass of gases and solids in the container?
Two curves on the same concentration-versus-time graph show the reactant $[A]$ being consumed under two conditions. Curve 1 drops more steeply at the beginning and levels off sooner than Curve 2. Which statement best compares the reaction rates?
A student mixed aqueous solutions of sodium carbonate (Na $_2$ CO $_3$ ) and calcium chloride (CaCl $_2$ ) to form a precipitate. In each condition, $10.0\,\text{mL}$ of $0.50\,\text{M}$ Na $_2$ CO $_3$ was mixed with $10.0\,\text{mL}$ of CaCl $_2$ at different concentrations. After 5 minutes, the mixture was filtered and the mass of dry precipitate collected was measured. What pattern do the data show?

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