Practice Test 15 - High School Chemistry

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

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1. Iron reacts with chlorine to form iron(III) chloride: $\mathrm{2Fe + 3Cl_2 \rightarrow 2FeCl_3}$. What is the mole ratio of $\mathrm{Fe}$ to $\mathrm{Cl_2}$?
2. A student claims: "Adding a catalyst increases the rate of decomposition of hydrogen peroxide." Setup: Two identical flasks each contained 50.0 mL of 3% hydrogen peroxide at 25°C. Flask 1 had no catalyst. Flask 2 had a small amount of manganese dioxide (MnO$_2$). The student measured the volume of oxygen gas collected after 60 seconds. Which statement best evaluates whether the evidence supports the claim?
3. Nitrogen monoxide forms as $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}.$ If $1.0\ \text{mol}$ of $\text{N}_2$ reacts with $3.0\ \text{mol}$ of $\text{O}_2$, which statement is correct?
4. Sulfur (S, atomic number 16) is in group 16 and commonly forms S. Which statement best explains the formation of S from a neutral sulfur atom?
5. A student mixes 5 mL of clear Solution A with 5 mL of clear Solution B in a test tube. Data and observations: - Before mixing: both solutions are clear and colorless at 20.0°C. - Immediately after mixing: the test tube feels cool; temperature drops to 16.5°C. - The mixture turns pale yellow over 30 seconds. - A faint odor (different from either original solution) is noticed when wafted. - No bubbles are observed and no solid forms. Did a chemical reaction occur? Choose the best CER justification.
6. Carbon (C) has 4 valence electrons (electron configuration ends in 2s² 2p²). Carbon commonly forms compounds like CH₄ and CO₂. How does carbon's valence electron structure explain its bonding tendency?
7. A school is replacing a section of drain pipe under a science lab sink. The sink is used to rinse glassware that may have traces of dilute acids, dilute bases, and salt solutions. The pipe must last for years without leaking, and a key constraint is that it cannot release toxic substances into wastewater. Which chemical properties are most important for the pipe material?
8. A student mixes two solutions at room temperature. During mixing, the beaker becomes noticeably cold, and the liquid changes from clear to cloudy with tiny solid particles visible. Which observations support the claim that a chemical reaction occurred?
9. A sodium ion, Na⁺, forms when sodium (atomic number 11) loses one electron. What is the electron configuration of Na⁺?​
10. A disposable hand warmer (iron powder inside a packet) is opened and shaken. After 5 minutes, its temperature rises from $20^\circ\text{C}$ to $41^\circ\text{C}$ without any external heating. Which choice best describes the energy transfer?
11. A student mixes 10.0 mL of blue copper(II) sulfate solution (CuSO4(aq)) with 10.0 mL of clear sodium hydroxide solution (NaOH(aq)). Before mixing: - CuSO4(aq): mass = 10.8 g, temperature = 23.0°C, color = blue/clear - NaOH(aq): mass = 10.5 g, temperature = 23.0°C, color = clear/colorless After mixing: - Mixture: mass = 21.3 g, temperature = 24.0°C, appearance = cloudy with a light blue solid present Which combination of data points most strongly supports that a chemical change occurred?
12. A neutral atom has 17 protons and mass number 37. How many electrons does it have?
13. A student claims: "Heating a reactant mixture increases the reaction rate." The student times how long it takes for a visible color change to occur in the same reaction mixture at different temperatures. Evidence (one trial each): - At 15°C: color change at 120 s - At 25°C: color change at 70 s - At 35°C: color change at 45 s - The beaker was stirred faster in the 35°C trial than in the 15°C trial. How well do the data support the claim?
14. A reactant $Z$ is consumed during a reaction. The concentration–time curve for $[Z]$ starts steep and then becomes less steep. Which statement best explains what the changing slope indicates?
15. A student investigated how temperature affects the solubility of potassium nitrate, KNO$_3$(s), in water. In each condition, 100.0 g of water was used and the maximum mass of KNO$_3$ that dissolved completely was recorded. Data table: - Temperature (°C): 20.0, 40.0, 60.0, 80.0 - Mass of KNO$_3$ dissolved (g per 100.0 g H$_2$O): 31.6, 63.9, 109.0, 169.0 What relationship do the data reveal between temperature and solubility of KNO$_3$ in water?
16. In a classroom demo, a small piece of sodium metal (Na), located in Group 1 and Period 3, reacts quickly and vigorously when dropped into water. Which justification best explains this observation using periodic trends and atomic structure?
17. Arrange these halogens (Group 17) by decreasing reactivity (most reactive to least reactive): fluorine (F, Period 2), chlorine (Cl, Period 3), and bromine (Br, Period 4).
18. Arrange the following elements in order of increasing atomic radius (smallest largest): carbon (C) is in period 2 group 14, silicon (Si) is in period 3 group 14, and tin (Sn) is in period 5 group 14.
19. Given the balanced equation: $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$ If $2.5$ mol of $\text{CaCO}_3$ decompose completely, how many moles of $\text{CO}_2$ are produced?
20. A student accidentally left a cup of clear sports drink (mostly water, sugar, and dyes) uncovered overnight. In the morning, the drink looks darker and slightly sticky on the sides of the cup. The student is unsure whether a chemical change occurred or if it was only water evaporating (a physical change). Design an investigation to test whether the overnight change involved a chemical reaction. Which investigation design best answers the testable question, using clear variables, fair controls, and appropriate evidence to collect?

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