Practice Test 18 - High School Chemistry

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

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1. A company producing compostable takeout containers chose polylactic acid (PLA) over conventional polyethylene (PE) for a pilot program to reduce long-term plastic waste. In an industrial composting test (high humidity and elevated temperature), PLA containers lost most of their mass within 12 weeks, while PE containers showed no visible change. However, PLA containers softened if hot soup sat in them for 30 minutes. Which option best justifies the decision to use PLA for the pilot, acknowledging trade-offs using chemical properties and evidence?
2. Balance the double replacement reaction using the smallest whole-number coefficients: AgNO3 + NaCl → AgCl + NaNO3​​
3. In a displacement test, chlorine gas (Cl$_2$, a Group 17 halogen in period 3) is bubbled through a solution of potassium bromide (KBr), which contains bromide ions from bromine (Br, period 4). Will chlorine displace bromine from potassium bromide?
4. Determine the correct coefficients to balance the equation using the smallest whole numbers: Zn + HCl → ZnCl2 + H2
5. Chlorine has electron configuration [Ne]3s2 3p5 and bromine has electron configuration [Ar]4s2 4p5. Bromine has a lower first ionization energy than chlorine. Which explanation using electron configuration is best?
6. Given the balanced equation: $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ If $5.0$ mol of $\text{H}_2$ react completely, how many moles of $\text{H}_2\text{O}$ are produced?
7. A student mixes baking soda (NaHCO$_3$) with citric acid solution in a cup on a balance (open to air). Data: - Before: 3.00 g NaHCO$_3$ + 60.00 g citric acid solution, 23.0°C (total = 63.00 g) - After fizzing stops: mass of cup contents = 61.90 g, 22.0°C, no solid remains; bubbles observed during mixing Which interpretation best explains the mass change?​
8. A school chemistry lab replaced glass reagent bottles with high-density polyethylene (HDPE) bottles for storing 1 M hydrochloric acid (HCl). The lab noted that over a semester, some glass stoppers became stuck and a few bottles showed etched markings near the neck, while the HDPE bottles did not show visible damage or leaks. Which reasoning best justifies switching to HDPE for this use?
9. A student bends a copper wire into a spiral. Before, it is straight and shiny; after, it is the same shiny copper but in a different shape. Is this a physical or chemical change?
10. A student reacts a strip of magnesium ribbon with 50 mL of 1.0 M hydrochloric acid (HCl) in a beaker at 20°C. The magnesium fizzes as hydrogen gas forms. The student repeats the experiment but warms the acid bath so the reaction starts at 35°C, keeping the acid concentration, volume, and magnesium strip size the same. Based on collision theory, how will the reaction rate change at 35°C compared with 20°C?
11. Displacement reaction (halogens): Chlorine (Cl, Group 17 Period 3) is bubbled through a solution of potassium bromide (contains $Br^-$). Will chlorine displace bromine (form bromine) from the bromide compound?
12. A student reacts baking soda (sodium bicarbonate, NaHCO3) with vinegar (acetic acid solution) in an open flask.

    Measurement	Before mixing	After reaction stops
    Mass of empty flask	120.00 g	120.00 g
    Mass of vinegar added	50.00 g	—
    Mass of NaHCO3 added	5.00 g	—
    Mass of flask + contents	175.00 g	172.30 g
    Visible bubbling	none	stopped

    Which interpretation best explains the mass change?
13. Balance the chemical equation using the smallest whole-number coefficients (do not change subscripts): CH4 + O2 → CO2 + H2O​
14. A neutralization reaction is measured to have $\Delta H = -57\ \text{kJ}$ for the reaction as written. What should happen to the temperature of the surroundings during the reaction (assuming heat is not lost to the outside environment)?
15. Lithium (Li), sodium (Na), and potassium (K) are all in group 1. Each reacts vigorously with water and forms a +1 ion (Li⁺, Na⁺, K⁺). Why do these elements show similar chemical behavior?
16. Consider these elements from period 3: sodium (Na, group 1), magnesium (Mg, group 2), and aluminum (Al, group 13). They can form Na\u207a, Mg\u00b2\u207a, and Al\u00b3\u207a ions, respectively. Which statement best explains the pattern in ion charges using valence electrons?​
17. Sulfur burns in oxygen according to $\mathrm{S + O_2 \rightarrow SO_2}$. If $2.5 \, \text{mol}$ of $\mathrm{SO_2}$ are produced, how many moles of $\mathrm{O_2}$ were consumed?
18. Using the Aufbau filling order (1s, 2s, 2p, 3s, 3p...), what is the full electron configuration of sulfur (S), atomic number 16?
19. In the nuclear equation $^{238}_{92}\mathrm{U} \rightarrow {}^{234}_{90}\mathrm{Th} + X$, what particle is represented by $X$?
20. Magnesium (Mg) is in group 2 with electron configuration ending in 3s². Chlorine (Cl) is in group 17 with electron configuration ending in 3s² 3p⁵. Magnesium forms Mg²⁺ ions, while chlorine forms Cl⁻ ions. Which statement best explains these different ion charges using valence electrons?

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