Practice Test 7 - High School Chemistry

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

In a demonstration, lithium (Li), sodium (Na), and potassium (K) are each placed in separate beakers of water. Observations show the reactions become more vigorous from Li to Na to K. Which justification best explains this pattern using periodic trends?
In the fusion equation $^{2}_{1}\mathrm{H} + \,^{3}_{1}\mathrm{H} \rightarrow \,^{4}_{2}\mathrm{He} + \,^{1}_{0}\mathrm{n}$ , what particle is produced along with helium-4?
Which scenario describes fusion rather than fission or radioactive decay?
A student claims: "If a reaction releases heat, that means breaking bonds must release energy." Which statement best corrects the student using bond-energy ideas?
Magnesium (Mg) is in Group 2 and commonly forms $\text{Mg}^{2+}$ . Its electron configuration ends in $3s^2$ . Why does magnesium form a $2+$ ion instead of a $1+$ ion?
Balance the equation (smallest whole-number coefficients): Ca(OH)2 + HCl → CaCl2 + H2O
A student claims: "A reaction occurred that produced a gas when hydrogen peroxide was added to a potato slurry." Evidence: 1) Many bubbles formed and accumulated as foam. 2) A glowing splint inserted near the foam relit. 3) The potato slurry was brown before and after. 4) The beaker was placed on a white piece of paper. Which evidence best supports the specific idea that a gas was produced (not just that something changed)?
A single-step reaction energy diagram shows reactants at 60 kJ and products at 95 kJ (with one peak in between). What does the diagram indicate about the overall energy change, $\Delta H$ ?
A student is building a simple electrolysis setup to split water with a small battery. The electrodes will be in salty water (to increase conductivity). Requirements: (1) electrode should resist corrosion as much as possible for repeated use, (2) should be safe for a classroom, and (3) must fit a very small budget. Options: - Graphite (carbon) rod: relatively inert; inexpensive; can slowly wear/flake. - Iron nail: very cheap; corrodes/rusts quickly. - Copper wire: moderate cost; can corrode and release copper ions into solution. Which electrode material is the best trade-off for repeated classroom trials?
A school is replacing old drinking-water plumbing in a 1960s building. The original pipes were copper, but recent water tests showed blue-green staining in sinks and elevated dissolved copper after the city switched to a slightly more acidic water supply (pH 6.4). The renovation team chose to install PEX (cross-linked polyethylene) tubing for most indoor runs instead of new copper. Which reasoning best justifies choosing PEX over copper for this application using chemical properties and the evidence provided?
Carbon (C) has 4 valence electrons (electron configuration ends in 2s² 2p²). In many compounds, carbon forms 4 covalent bonds (for example, CH₄). How does carbon's valence electron structure explain its bonding tendency?
A research lab uses small amounts of radioactive tracers to follow how a chemical moves through a plant. This can improve understanding of nutrient uptake and support agricultural research, but it also introduces radiation hazards if materials are mishandled and requires secure storage and disposal. Which statement best balances the benefits and risks of using tracers?
A student predicts that potassium (K) will react more vigorously with water than sodium (Na). Both are in Group 1, but potassium is below sodium in the group. Which reasoning best supports this prediction using periodic trends and atomic structure?
Two unlabeled white powders in the lab are either cornstarch or calcium carbonate (chalk). A student claims, "Both will react chemically with vinegar." Your class needs to test the claim using observable evidence without specialized instruments. Which investigation design best tests whether each powder undergoes a chemical change when vinegar is added?
A concentration-versus-time graph shows reactant $[A]$ decreasing for two trials. Trial 1 and Trial 2 start at the same initial concentration. Trial 1 decreases gently at first and then becomes steeper later. Trial 2 decreases steeply at first and then becomes gentle later. Which statement is true based on the graph shapes?
In the fusion equation $^{2}_{1}\mathrm{H} + {}^{2}_{1}\mathrm{H} \rightarrow {}^{3}_{2}\mathrm{He} + {}^{1}_{0}\mathrm{n},$ which statement best describes what is happening?
A student tested electrical conductivity of aqueous solutions using the same conductivity probe. Each solution was 0.10 M and at 22.0°C. Data: - Distilled water: 5 $\mu$ S/cm (no visible change) - Sucrose(aq): 12 $\mu$ S/cm (no visible change) - NaCl(aq): 18,400 $\mu$ S/cm (no visible change) - HCl(aq): 41,200 $\mu$ S/cm (no visible change) Which conclusion is supported by the data?
The following elements are all in period 3: sodium (Na) is in group 1, silicon (Si) is in group 14, and sulfur (S) is in group 16. Which element has the least metallic character?
Balance the equation using the smallest whole-number coefficients (do not change subscripts): Na + Cl2 → NaCl
Scientists use radioactive dating to estimate the age of materials: carbon-14 dating can help date once-living objects (like wood or bone), while uranium-based methods can date very old rocks. These techniques have advanced archaeology and geology, but they require safe handling of radioactive sources and careful interpretation to avoid incorrect conclusions. Which statement best balances benefits and concerns?

Practice tests