Practice Test 6 - 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 student team designs a reusable spray bottle to hold a homemade bathroom cleaner containing 5% acetic acid (vinegar) and a small amount of salt. They choose an uncoated steel spring for the trigger because steel is strong and inexpensive. After 2 weeks of daily use, the trigger becomes stiff and orange-brown rust appears on the spring. The bottle still seals and does not leak. Based on the test results, which refinement would best address the failure while keeping the trigger strong?
2. Consider the balanced equation $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2.$ According to the coefficients, how many moles of $\text{HCl}$ are needed to react with 1 mole of $\text{Zn}$?
3. Sodium chloride (NaCl) is a solid with a high melting point and is used as road salt because it stays solid in warm weather. Which justification best explains NaCl's high melting point using the properties of sodium and chlorine?
4. A class investigates: How does water temperature affect how fast sugar dissolves? Students pour 100 mL of water into each of three identical cups and adjust the water to 20C, 40C, and 60C using a hot plate and thermometer. They add 10.0 g of granulated sugar to each cup and stir each cup at the same rate (one круг per second) using the same type of stir rod. They start a timer when sugar is added and stop it when no solid sugar is visible. What is the dependent variable in this investigation?
5. An element has atomic number $Z=13$ and mass number $A=27$ (a neutral atom). How many neutrons does it have?
6. A school is installing new chemical waste drain pipes for a lab sink that will carry mostly dilute acids and bases at room temperature (typically 20–30°C). The pipe must be safe for indoor use (no toxic metal leaching), reasonably durable, and the school has a tight budget. Which material is the best trade-off for this application? Consider these options: - PVC plastic: excellent resistance to many dilute acids/bases; low cost; softens if exposed to high heat. - Copper: moderate cost; can corrode in acidic solutions over time; very heat-tolerant. - Stainless steel: excellent corrosion resistance; high cost; very durable. - Plain carbon steel: low cost; rusts/corrodes quickly in wet, acidic/basic conditions; durable mechanically.
7. A prototype clear window is made for a small greenhouse. Initial design: PVC sheet was selected because it is inexpensive and easy to cut. Test evidence (outdoor exposure): after 4 months in sunlight, the sheet turns yellow and becomes brittle; small cracks appear near screw holes. A similar sheet stored indoors stays flexible and clear. Which refinement best targets the problem indicated by the evidence while keeping the window clear and affordable?
8. An atom has atomic number $Z=7$ and mass number $A=14$. How many neutrons are in its nucleus?
9. A city is choosing a disinfectant for a public swimming pool. They selected sodium hypochlorite (liquid chlorine) rather than hydrogen peroxide. In trials at the same pool usage level, free chlorine stayed within the target range for 24 hours and bacterial counts stayed low, while hydrogen peroxide required frequent re-dosing and bacterial counts rose between doses. Which justification best supports the decision using chemical reasoning and evidence?
10. Consider a reaction described in words: "Reactant bonds are broken, atoms rearrange, and then new product bonds form." Which sequence best matches the energy changes along this pathway?
11. For the balanced reaction $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3,$ if $6.0\ \text{mol}$ of $\text{H}_2$ react completely, how many moles of $\text{NH}_3$ form?
12. In halogen displacement reactions, a more reactive halogen can displace a less reactive halogen from its salt solution. Reactivity decreases down Group 17. If chlorine gas is bubbled through a potassium bromide (KBr) solution, what is the correct prediction?
13. Oxygen (O) is in Group 16 and has 6 valence electrons (electron configuration ends in $2s^2\,2p^4$). Oxygen often forms two bonds in molecules like $\text{H}_2\text{O}$. Why does oxygen commonly form two bonds?
14. A camping stove manufacturer needs a flexible fuel line that may be exposed to small spills of liquid fuel and to heat from nearby burners. The line material must not dissolve or weaken from fuel contact, must not release toxic fumes when warmed, and must not be easily ignited if briefly exposed to a flame. Which chemical properties are most important?
15. A school chemistry lab needs new bottles to store 6 M hydrochloric acid (HCl). The lab considered soda-lime glass, aluminum, and high-density polyethylene (HDPE). They selected HDPE bottles. After 6 months, the HDPE bottles showed no leaks or visible degradation, while an aluminum test container developed pitting and a cloudy solution formed. Which justification best supports selecting HDPE?
16. Aluminum (Al) has electron configuration [Ne]3s2 3p1 and silicon (Si) has electron configuration [Ne]3s2 3p2. Both are in period 3. Silicon has a higher first ionization energy than aluminum. Which configuration-based explanation is best?
17. A student places a steel wool pad in a jar with a small amount of water at the bottom (the steel wool does not touch the liquid). The jar is loosely covered and left on a windowsill for 3 days. Observations: - Day 0: steel wool is shiny gray. - Day 3: steel wool has a reddish-brown coating and looks flaky in places. - The mass of the steel wool increases from 3.20 g to 3.44 g. - No melting or dissolving is observed. Based on the evidence, did a chemical reaction occur? Choose the best CER-style justification.
18. These elements are all in period 2: lithium (Li) is in group 1, carbon (C) is in group 14, and fluorine (F) is in group 17. Which element is most electronegative?
19. A single-step energy diagram shows reactants at 100 kJ, products at 60 kJ, and a peak at 170 kJ. Which statement correctly identifies $\Delta H$ for the reaction?
20. Iron reacts with oxygen in air to form rust (iron(III) oxide): $4\text{Fe}(s) + 3\text{O}_2(g) \rightarrow 2\text{Fe}_2\text{O}_3(s)$ A piece of steel wool has a mass of 20 g. After being left in moist air for several days, the rusted wool has a mass of 27 g. Which statement best explains the mass increase?

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