Practice Test 25 - High School Chemistry

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

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1. What coefficient of H2O is needed to balance the equation using the smallest whole numbers? C2H6 + O2 → CO2 + H2O​​
2. A student claims: "Heating a glow stick makes it glow brighter because the chemical reaction happens faster." Evidence: 1) Glow stick A kept at 10°C appeared dim. 2) Glow stick B kept at 40°C appeared brighter. 3) Both glow sticks were the same brand and activated at the same time. 4) Glow stick B stopped glowing sooner than glow stick A. How well does the evidence support the claim?
3. A student mixes hydrogen peroxide solution (3%) with a small amount of yeast and claims, "It's just bubbling because the yeast is fizzy—no chemical change." Your class must design an investigation to determine whether a chemical change occurs and to collect evidence. Which plan is best and safe for a high school lab?
4. Compare the first ionization energies of magnesium (Mg) and sulfur (S). Mg: [Ne]3s2 (group 2, period 3). S: [Ne]3s2 3p4 (group 16, period 3). Sulfur has a higher first ionization energy than magnesium. Which statement best explains why using electron configuration ideas?
5. A student reacts vinegar (acetic acid solution) with baking soda (sodium bicarbonate) in an open cup and records masses. Before mixing: - Cup + 50.0 g vinegar: total mass = 120.0 g - Baking soda added: mass = 5.0 g After bubbling stops (still in open cup): - Cup + remaining mixture: total mass = 122.5 g What is the best interpretation of the mass data?
6. A patient with thyroid cancer is offered treatment with radioactive iodine (I-131). The doctor explains that I-131 is taken up by thyroid tissue and can destroy cancer cells, which can be life-saving. The doctor also explains that the patient will be exposed to radiation and may have side effects, so the dose is carefully controlled and safety instructions reduce exposure to family members. Which choice is the most balanced evaluation of this nuclear technology application?
7. A student performs the reaction of magnesium with hydrochloric acid at 25°C using identical pieces of magnesium: $\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$ They compare two acid concentrations while keeping all other conditions the same: - Trial A: 0.50 M HCl - Trial B: 1.5 M HCl Which trial has the faster reaction rate, and why?
8. Sulfur trioxide forms by: $2\text{SO}_2 + \text{O}_2 \rightarrow 2\text{SO}_3$ If $5.0\,\text{mol}$ of $\text{SO}_2$ and $3.0\,\text{mol}$ of $\text{O}_2$ are available, which reactant is the limiting reactant?
9. A student compares two ways to get energy: (1) burning gasoline in a car engine (a chemical reaction that rearranges electrons in bonds, typically a few eV per reaction) and (2) fission in a nuclear power plant (a nuclear reaction that changes the nucleus, typically MeV per reaction). Which statement best compares the energy released per atom in these two processes?
10. A single-step reaction energy diagram has reactants at 100 kJ, a peak at 160 kJ, and products at 140 kJ. Based on the diagram, which statement is correct?
11. A school is replacing a sink drain trap in a chemistry classroom. It will occasionally receive small amounts of dilute acids/bases and lots of water. Requirements: must resist corrosion from occasional chemicals, must handle hot water up to 70°C, and must be affordable. Which material best balances these competing criteria? Options: - Brass: durable; moderate cost; can corrode over time with some chemicals. - PVC: inexpensive; good corrosion resistance; can soften if exposed to very hot water but usually fine around 70°C. - Steel: strong and cheap; corrodes/rusts more easily with chemical exposure.
12. A student wants to test the effect of surface area on reaction rate using calcium carbonate and hydrochloric acid. The student plans to compare large chips vs powder. Which set of conditions should be kept the same to make it a fair test of surface area?
13. Lithium (Li), sodium (Na), and potassium (K) are all in group 1 (periods 2, 3, and 4 respectively). Arrange these elements in order of increasing atomic radius (smallest largest).
14. Dry ice is left on a lab table. Before, it is a solid; after a short time, the solid gets smaller and "fog" appears around it as it turns directly into a gas. Is this a physical or chemical change?
15. Sodium (Na) is in group 1 and has the electron configuration 1s² 2s² 2p⁶ 3s¹. A small piece of sodium reacts vigorously with water and forms Na⁺ ions. How does sodium's atomic structure explain this chemical behavior?
16. Which nuclear equation shows alpha decay?
17. Two metals from Group 2 are tested in room-temperature water: magnesium (Mg, Period 3) and calcium (Ca, Period 4). Which is expected to react faster with water based on periodic trends?
18. A student mixes 10 mL of clear vinegar with 10 mL of clear liquid soap solution in a cup. Observations: - The mixture becomes cloudy and forms lots of foam when stirred. - No sustained bubbling occurs when the mixture sits (the foam slowly collapses over 5 minutes). - Temperature stays at 20.5°C before and after mixing. - When the mixture is left undisturbed for 30 minutes, it separates into two layers. Based on the evidence, which CER-style justification is best supported?
19. Students investigate: "How does the identity of a metal affect its reaction with hydrochloric acid?" They place 50.0 mL of 2.0 M HCl into three separate beakers at room temperature. They add a 3.0 cm × 1.0 cm strip of zinc to Beaker 1, iron to Beaker 2, and copper to Beaker 3. They observe for 5 minutes and record the total volume of gas produced using an inverted graduated cylinder. Which list contains only controlled variables for this investigation?
20. For the reaction $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O},$ you start with 3.0 mol of $\text{H}_2$ and 2.0 mol of $\text{O}_2$. Which reactant is the limiting reactant (runs out first)?

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