Practice Test 2 - High School Chemistry

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

A piece of paper is torn in half. Before, it is one sheet; after, it is two smaller pieces of paper. Which best describes the change?
A student adds a few drops of one clear solution to another clear solution in a cup. The mixture suddenly turns bright yellow and remains yellow even after stirring. No solid appears. Which observation best indicates a chemical reaction occurred?
A product $P$ forms during a reaction. The concentration–time graph shows $[P]$ increasing quickly at first and then leveling off. Based on the shape of the curve, how does the reaction rate change over time?
Bromine (Br) is a Group 17 element with atomic number 35. It forms the ion Br. Which statement best explains the formation of Br from Br?
A city wants to reduce corrosion in a coastal boardwalk lighting system. The previous design used bare copper wire connections inside metal junction boxes, and after 2 years many connections failed due to green corrosion products and increased electrical resistance. The redesign uses tinned copper connectors (copper coated with tin) and sealed gel-filled caps. Which justification best explains why this change improves performance in salty air?
A student mixes 25 mL of clear Solution A (labeled "calcium chloride, $\text{CaCl}_2(aq)$ ") with 25 mL of clear Solution B (labeled "sodium carbonate, $\text{Na}_2\text{CO}_3(aq)$ ") in a foam cup. The mixture turns cloudy within 10 seconds and a white solid settles after 3 minutes. The cup feels slightly warmer. Observations and data: - Initial appearance: both solutions clear and colorless - After mixing: cloudy mixture; white solid forms and settles - Temperature: $22.0^\circ\text{C}$ before, $26.0^\circ\text{C}$ after 2 minutes - Gas: no bubbling observed - Filtration: solid remains on filter paper; rinsing with water does not dissolve it Did a chemical reaction occur? Choose the justification that best supports your conclusion using claim-evidence-reasoning (CER).
A single-step reaction energy diagram shows reactants at 65 kJ and products at 65 kJ, with a peak above them. What is the best conclusion about the overall energy change $\Delta H$ ?
A neutral atom has 2 electrons in the first shell, 8 electrons in the second shell, and 3 electrons in the third shell (shell model: 2-8-3). Which electron configuration matches this atom?
A student engineering team must choose a material for a portable container that will hold a basic cleaning solution (pH ~12) for custodial staff. Requirements: non-toxic for routine handling (critical), chemical resistance to bases (critical), and light weight (important). Cost matters but is not the top priority. Material options: - Glass: chemically resistant; non-toxic; heavy and breakable. - Polypropylene (PP) plastic: good resistance to bases; lightweight; generally considered low toxicity for this use; can deform if exposed to high heat. - Mild steel: strong; inexpensive; can corrode/rust in wet basic environments over time. Which material best balances the competing criteria?
A student claims: "The reaction between baking soda and vinegar is endothermic." Evidence collected: 1) The temperature of the mixture dropped from 24.0°C to 19.5°C without any external cooling. 2) Bubbles formed rapidly when the substances were mixed. 3) The student heard a fizzing sound. 4) The vinegar label said it was 5% acidity. Which statement best evaluates the claim using the evidence?
A student reacts a strip of magnesium ribbon with $25\,\text{mL}$ of $1.0\,\text{M}$ hydrochloric acid (HCl) at $22^\circ\text{C}$ . The bubbling (hydrogen gas) is steady and the magnesium disappears in about 60 seconds. The student then repeats the reaction but warms the acid to $35^\circ\text{C}$ , keeping the acid volume, concentration, and magnesium strip the same. Based on collision theory, how will the reaction rate change?
Scientists use radioactive dating (such as carbon-14 for once-living materials) to estimate the age of archaeological finds. This helps build timelines of human history, but it requires handling radioactive materials and instruments, and results can be misinterpreted if samples are contaminated. Which choice best evaluates the benefits and risks/limitations of this nuclear process?
A student claims: "Zinc is more reactive than copper in hydrochloric acid." In a controlled test, equal-sized pieces of zinc and copper are placed into separate beakers containing 50 mL of 1.0 M HCl at 25°C. Evidence: 1) Zinc produces many bubbles immediately; copper produces no visible bubbles after 5 minutes. 2) The zinc piece becomes smaller after 10 minutes; the copper piece looks unchanged. 3) Both beakers are made of glass. 4) The zinc sample is gray and the copper sample is reddish-brown. Which statement best evaluates the claim using the evidence?
A student reacts calcium carbonate with hydrochloric acid to produce carbon dioxide gas: $\text{CaCO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow \text{CaCl}_2\text{(aq)} + \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)}$ They keep the acid concentration at 1.0 M and use the same mass of calcium carbonate powder each time. They propose cooling the reaction mixture from 30°C to 10°C. What will happen to the reaction rate, and why?
A student reacts 15 g of calcium carbonate in an open flask: CaCO $_3$ (s) → CaO(s) + CO $_2$ (g). After heating, 9 g of solid CaO remains in the flask. Which statement best explains why 6 g of mass seems to be missing?
A student places 10 g of candle wax in a metal spoon and warms it over hot water (like a double boiler) until it becomes a liquid. The student then removes the spoon and lets it cool. Observations/data: - Wax changes from solid to liquid when warmed - No odor change and no smoke - Temperature of wax: $25^\circ\text{C}$ (solid) $\rightarrow$ $65^\circ\text{C}$ (liquid) - When cooled back to room temperature, the wax becomes a solid again Based on the evidence, did a chemical reaction occur? Choose the best CER justification.
Two glove materials were tested for a lab activity using dilute ammonia solution (a weak base). The goal is safe handling for 30-minute labs while keeping good dexterity. Test results: - Latex gloves: remained flexible, but after 30 minutes developed a slight sticky feel and a strong odor. - Nitrile gloves: no stickiness or odor after 60 minutes, but students reported slightly less flexibility. Which refinement best uses the evidence to improve the design choice for the lab?
Magnesium (Mg) is a group 2 element with atomic number 12. A neutral Mg atom commonly forms Mg. Which explanation best accounts for the +2 charge?
A student adds a small amount of steel wool to a test tube containing 10 mL of copper(II) sulfate solution (blue). The test tube is left undisturbed for 20 minutes. Observations/data: - Blue solution becomes lighter blue over time - A reddish-brown coating forms on the steel wool - Some dark particles fall to the bottom - No bubbling observed - Temperature remains about $22^\circ\text{C}$ Did a chemical reaction occur? Choose the best CER justification.
A student drops a piece of magnesium metal into a cup containing hydrochloric acid. Within seconds, the liquid fizzes vigorously, the metal gets smaller and smaller, and the cup feels warm to the touch. Which observation is evidence that a chemical reaction occurred?

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