Practice Test 42 - High School Chemistry

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

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1. To investigate "How does salt concentration affect the boiling point of water?", students add NaCl to make three solutions using the same hot plate and identical 250 mL beakers. Each beaker starts with 200 mL of water; they dissolve 0.0 g, 10.0 g, or 20.0 g of NaCl, then heat each solution and record the temperature when a steady rolling boil is reached. Which factor is the dependent variable?
2. An unknown element X is in period 3, group 1. It has 1 valence electron in the third energy level. Which chemical behavior is most likely for element X based on its valence electrons?
3. A fusion reaction is written as $^{2}_{1}\text{H} + ^{2}_{1}\text{H} \rightarrow ^{3}_{2}\text{He} + X.$ What is particle $X$?
4. A student is choosing a material for a beaker used to heat saltwater to near boiling on a hot plate. Requirements: (1) must tolerate high temperature without melting, (2) should not corrode in saltwater, (3) safety matters (avoid toxic materials), and (4) cost should be reasonable for a classroom. Which option is the best compromise? Materials: - Borosilicate glass: excellent heat resistance; good chemical resistance; but can shatter if dropped. - Polystyrene plastic: very cheap and light; but softens/melts at relatively low temperatures. - Aluminum: won't melt at these temperatures; but can corrode in salty water and may contaminate the solution.
5. A student mixed 10.0 mL of 0.10 M AgNO$_3$(aq) with 10.0 mL of 0.10 M NaCl(aq) at room temperature and recorded observations. The mixture was then filtered and the mass of dried solid was measured. The procedure was repeated for three trials. Table: Observations and precipitate mass

   Trial	Observation immediately after mixing	Mass of dried precipitate (g)
   1	Cloudy white solid formed	0.141
   2	Cloudy white solid formed	0.139
   3	Cloudy white solid formed	0.142

   Which statement best describes the pattern in the data?
6. A student reads: "Burning 1 kg of coal releases on the order of tens of millions of joules, while fissioning 1 kg of uranium releases on the order of tens of trillions of joules." No exact calculation is needed. Which conclusion is most reasonable and consistent with the typical eV (chemical) vs MeV (nuclear) energy scales?
7. A student mixes two solutions. During mixing, the liquid turns from clear to bright yellow, and a strong new odor is noticed. Which observations support the claim that a chemical reaction occurred?
8. A nuclear power plant commonly produces energy when uranium nuclei split into smaller nuclei. Which process is responsible for the energy production in this description?
9. Which represents the correctly balanced equation (smallest whole-number coefficients)? Fe + O2 → Fe2O3
10. A nucleus of americium in a smoke detector gives off alpha particles over time. No second nucleus is involved, and the nucleus is not splitting into two similar-sized pieces. What type of nuclear process is this?
11. A student mixes two liquids in a cup. During mixing, a strong new odor is noticed, steady bubbling occurs (not from heating), and the cup feels warmer. Select the set of observations that best indicates a chemical reaction occurred.
12. A medical device company is choosing a metal for bone screws that will remain in the body for years. They selected titanium alloy instead of carbon steel. In simulated body fluid testing for 12 weeks, titanium showed negligible corrosion and no visible rust, while carbon steel developed corrosion products. Which justification best supports the choice?
13. A student mixes hydrochloric acid (HCl(aq)) with magnesium metal (Mg(s)) in a sealed container and measures mass. Data: - Before mixing: 40.00 g HCl(aq) (clear, 20.0°C) + 1.00 g Mg(s) - After reaction stops: container contents mass = 41.00 g, temperature = 28.0°C, appearance = clear solution with no Mg(s) remaining; gas is visible in the headspace Which statement best interprets the data?​
14. A student reacts identical pieces of magnesium ribbon with hydrochloric acid at 25°C. The only change is the acid concentration. Trial A: 0.25 M HCl; slow bubbling; magnesium disappears in ~160 s Trial B: 1.0 M HCl; faster bubbling; magnesium disappears in ~40 s Which statement is the best conclusion about concentration and reaction rate for these trials?
15. Using the Aufbau filling order (1s, 2s, 2p, 3s, 3p), what is the electron configuration of magnesium (Mg), atomic number 12?​
16. In the reaction $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$, which set of bond changes correctly describes what happens?
17. Elements lithium (Li), sodium (Na), and cesium (Cs) are all in group 1 (alkali metals). Li is in period 2, Na is in period 3, and Cs is in period 6. Which element has the largest atomic radius?
18. A science club discusses why a tiny uranium fuel pellet can replace a large pile of coal for producing electricity. They note that chemical reactions (like burning coal) rearrange electrons and chemical bonds (eV scale), while nuclear reactions (like fission) change the nucleus (MeV scale). Which choice best explains why nuclear fuel has much higher energy density (energy per kilogram) than chemical fuel?
19. Rubidium (Rb) is in group 1 period 5, and calcium (Ca) is in group 2 period 4. Based on periodic trends, which element has the greater metallic character?
20. Hydrogen peroxide is poured onto a cut and immediately begins fizzing, producing many bubbles on the skin. Before, it is a clear liquid with no bubbles; after, bubbles form and the fizzing continues for a short time. Which best describes the change?

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