Practice Test 41 - High School Chemistry

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

A student spills clear sports drink on a hot plate set to low heat. After several minutes, the liquid becomes thicker and darker, and a sticky brown residue remains. The lab assistant needs to know whether this was only water evaporating (physical change) or whether the sugars in the drink underwent a chemical change that could produce new substances and stronger odors. Design the best investigation to test whether heating the sports drink causes a chemical change rather than only evaporation. Which plan most appropriately identifies variables, uses a comparison/control, and specifies evidence to collect?
A reactant $X$ is being consumed. Two points, $t_1$ (early) and $t_2$ (later), are marked on the concentration–time curve. At which time is the reaction rate larger in magnitude?
Helium (He), in group 18 and period 1, has the lowest boiling point of any element and remains a gas even near extremely low temperatures. Which justification best explains helium's very low boiling point using atomic structure and intermolecular attraction ideas appropriate for periodic trends?
Given the balanced equation: $2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3$ How many moles of $\text{Cl}_2$ are needed to react completely with $4.0$ mol of Al?
In everyday life, a phone battery (chemical) might last about a day, while some spacecraft use radioisotope batteries (nuclear decay) that can provide power for years or decades. Which statement best explains why the nuclear option can have such high energy density (energy per unit mass)?
Two clear, colorless liquids are mixed in a sealed plastic bag: 50 mL of water and 10 mL of isopropyl alcohol. The bag is gently stirred. Observations and measurements: - The mixture remains clear and colorless. - Temperature changes from 21.0°C to 23.0°C. - No bubbles are seen. - No solid forms. - When the bag is opened after 5 minutes, it smells strongly of alcohol. Is there sufficient evidence to conclude a chemical reaction occurred? Choose the best CER justification.
A school's maintenance team stores a strong drain cleaner (a highly basic solution) for clearing clogs. The container must not weaken, leak, or corrode during storage, and it must not release toxic substances into the air of a small storage closet. Which set of chemical properties is most important for the container material?
A student claims: "A chemical reaction occurred when solid A was mixed with liquid B." Evidence/observations recorded: 1) Bubbles formed immediately and continued for about 30 seconds. 2) The mass of the closed container stayed the same (within $\pm 0.01\,\text{g}$ ). 3) The mixture changed from clear to cloudy. 4) The beaker felt cold to the touch. Which statement best evaluates the claim using the evidence?
An ion has 11 protons, 12 neutrons, and 10 electrons. What is the charge on the ion?
Chlorine (Cl) is in group 17 and has 7 valence electrons. Chlorine often forms the ion Cl⁻ when reacting with metals. Why does chlorine form a $-1$ ion?
A student mixes solutions and then filters the mixture. Before mixing: - 40.0 mL lead(II) nitrate solution, Pb(NO3)2(aq): mass = 44.0 g, clear/colorless, 20.0°C - 40.0 mL potassium iodide solution, KI(aq): mass = 43.5 g, clear/colorless, 20.0°C - Total mass before: 87.5 g After mixing and filtering: - Yellow solid collected (dried): mass = 3.6 g - Filtrate (remaining liquid): mass = 83.9 g, clear/colorless - Total mass after (solid + filtrate): 87.5 g Which statement best interprets the data?
A student adds 5.0 g of table salt (sodium chloride, $\text{NaCl}$ ) to 100 mL of water in a beaker and stirs for 2 minutes. Observations and data: - Salt crystals disappear; solution becomes clear - Temperature: $23.0^\circ\text{C}$ before, $22.2^\circ\text{C}$ after stirring - No bubbles or odor observed - When the solution is left in a shallow dish overnight, water evaporates and white crystals reappear Based on the evidence, did a chemical reaction occur? Choose the best CER justification.
A student places a plant under a bright lamp. Over several hours, the plant produces oxygen bubbles in water, but the process stops when the lamp is turned off. Which statement best describes the energy change for photosynthesis in this setup?
Two reactions have the following enthalpy changes: Reaction 1: $\Delta H = -120\ \text{kJ}$ Reaction 2: $\Delta H = -45\ \text{kJ}$ Which reaction releases more heat to the surroundings as written?
A reaction is reported as "releases 120 kJ of heat to the surroundings per mole of reaction." Which $\Delta H$ value matches this description?
A single-step reaction energy diagram (Energy vs Reaction coordinate) shows reactants at 40 kJ, a peak at 110 kJ, and products at 20 kJ. Which part of the diagram represents the activation energy, $E_a$ ?
A concentration-versus-time graph shows the reactant concentration $[A]$ decreasing over time. The curve is very steep at the beginning and then gradually becomes almost horizontal (levels off) later. What does this graph indicate about how the reaction rate changes over time?
Students investigate: How does a catalyst affect the decomposition rate of hydrogen peroxide? They pour 30.0 mL of 3% H $_2$ O $_2$ into two identical flasks and keep both at 25C. In one flask they add 0.50 g of manganese(IV) oxide (MnO $_2$ ) and in the other they add nothing. They quickly attach a gas syringe to each flask and record the volume of oxygen gas collected after 60 seconds. Which list shows appropriate controlled variables (constants) for a fair test?
A community pool needs a material for a small pipe section carrying chlorinated water (mildly corrosive) at about 25–35°C. The pipe is indoors (no sunlight), and the main concerns are corrosion resistance and cost. High pressure is not expected. Which material is the best trade-off? Options: - Copper: durable; can corrode in some chlorinated conditions over time; moderate cost. - PVC: excellent corrosion resistance to chlorinated water; low cost; lower maximum temperature and can become brittle in cold conditions. - Stainless steel: excellent corrosion resistance; high cost.
A student drops identical tablets of an antacid (calcium carbonate) into 100 mL of vinegar at 25°C. All conditions are the same except the tablet form. Trial A: one whole tablet; bubbles for about 3 minutes Trial B: the same tablet crushed into small pieces; bubbles for about 1 minute Which factor most directly explains the faster bubbling in Trial B?

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