Practice Test 34 - 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 class investigates the question: How does the volume of reactant solution affect the amount of precipitate formed? They prepare four test tubes, each containing 10.0 mL of 0.50 M sodium carbonate ($\mathrm{Na_2CO_3}$). They then add different volumes of 0.50 M calcium chloride ($\mathrm{CaCl_2}$): 5.0 mL, 10.0 mL, 15.0 mL, and 20.0 mL. Each mixture is stirred for 10 seconds using the same stirring rod, then allowed to sit for 2 minutes. The precipitate is filtered, dried for 24 hours, and its mass is measured. Which set lists appropriate controlled variables in this investigation?
2. A single concentration-versus-time curve for reactant $[A]$ is shown below. The curve starts high, decreases steeply at first, then becomes more gradual and finally nearly flat. Which part of the curve corresponds to the slowest reaction rate?
3. A student heated potassium chlorate (KClO$_3$) to produce oxygen gas and compared trials with and without a MnO$_2$ catalyst. In each trial, $2.00\,\text{g}$ of KClO$_3$ was heated, and the time to collect $50.0\,\text{mL}$ of O$_2$ was recorded. What do the data indicate about the effect of MnO$_2$ on the reaction?
4. A student compared the effect of different salt solutions on the freezing point of water. Each solution was $100.0\,\text{mL}$ and cooled until the first ice crystals appeared; that temperature was recorded.

   Solution	Concentration (M)	Temperature when ice first appeared (°C)
   pure water	0.00	0.0
   NaCl(aq)	0.50	-1.6
   NaCl(aq)	1.00	-3.1
   NaCl(aq)	1.50	-4.7

   What conclusion is supported by the data?​
5. A cafeteria manager notices that apple slices sometimes turn brown quickly, but other times they stay lighter. They want to know whether the browning is a chemical change (new substances forming) and whether lemon juice slows it down for food quality reasons. Design an investigation to test: "Does coating apple slices with lemon juice reduce the rate of browning (a chemical change)?" Which plan best identifies variables, controls, and evidence to collect?
6. A company designed reusable drink bottles and compared aluminum (unlined), glass, and stainless steel. They chose glass for a line marketed as "no taste transfer" for citrus drinks. In a taste panel, citrus juice stored 48 hours in unlined aluminum bottles had a metallic taste and slightly higher dissolved metal levels, while glass bottles showed no detectable metal ions and no taste change. Which reasoning best supports choosing glass for citrus drinks?
7. A student combines two substances in a sealed container and records mass and temperature. Before: - Substance A (solid): mass = 6.0 g, temperature = 19.0°C, color = white - Substance B (liquid): mass = 14.0 g, temperature = 19.0°C, color = clear - Total mass (sealed container + contents): 120.0 g After shaking (still sealed): - Contents: temperature = 30.0°C, color = yellow, no visible pieces of solid A remain - Total mass (sealed container + contents): 120.0 g Which conclusion is best supported by the data?
8. A student designed a container to store bleach (sodium hypochlorite solution) and chose a clear PET plastic bottle because it is strong and transparent. Observations during a 6-week storage test in a sunny window: - The bleach lost strength faster than expected (less effective cleaning). - The bottle became slightly yellow and more brittle. - The same bleach stored in an opaque HDPE bottle kept its strength longer. Which refinement best matches the evidence?
9. A student designs a protective coating for a steel garden tool using a hard clear lacquer because it looks glossy and prevents rust at first. After a winter of temperature changes (warm days, freezing nights), the lacquer shows visible cracking, and rust appears mainly along the cracks. Areas without cracks remain rust-free. Which refinement most directly addresses the failure mode shown by the evidence while still using a clear protective coating approach?
10. A school robotics team needs a clear protective cover for a small battery pack on a robot that will be used outdoors. The cover may be splashed with rainwater and occasionally with salty water from puddles near roads in winter. The cover must not produce harmful fumes if it warms up in the sun and must not chemically react with the battery casing or corrode over time. Based on these conditions, what chemical properties are needed for the cover material?
11. Two different bonds are compared: Bond X is stronger than Bond Y. Which statement best matches the relationship between bond strength and energy changes?
12. A student compares two trials of the same reaction in solution. In Trial 1, the mixture is cold and reacts slowly. In Trial 2, the mixture is warm and reacts quickly. Which particle-level statement best explains why warming the solution increases the number of effective collisions?
13. Three nuclear changes are described below: 1) A heavy nucleus breaks apart into two smaller nuclei and releases neutrons. 2) Two light nuclei join to form one heavier nucleus. 3) One unstable nucleus emits a gamma ray but remains the same element. Which list correctly classifies 1), 2), and 3) in order?
14. A reaction coordinate diagram (Energy vs Reaction progress) for a single-step reaction starts at 80 units (reactants), rises to a peak at 140 units, and ends at 30 units (products). Which statement is correct?
15. A student mixes 50 mL of hydrochloric acid with 50 mL of sodium hydroxide in a foam cup. The thermometer reads $21^\circ\text{C}$ before mixing and $33^\circ\text{C}$ after mixing, and the cup feels warm. Based on these observations, is the reaction exothermic or endothermic, and what is the direction of energy flow?
16. Which description best matches radioactive decay?
17. A student studied how temperature affects the solubility of potassium nitrate (KNO$_3$) in water. The student added KNO$_3$ to $100\,\text{mL}$ of water at each temperature until a small amount of solid remained undissolved, then recorded the mass that had dissolved.

    Temperature (°C)	Mass of KNO$_3$ dissolved (g per 100 mL H$_2$O)
    20	32
    40	64
    60	110
    80	170

    What pattern does the data show?​
18. The ion $\text{O}^{2-}$ is oxygen with a $-2$ charge. If the isotope is oxygen-16 ($^{16}\text{O}$), how many electrons does $^{16}\text{O}^{2-}$ have?
19. Use the periodic trend for electronegativity. Compare these group 16 elements: - O (period 2) - S (period 3) - Te (period 5) Which element is least electronegative?
20. For the balanced reaction $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3,$ you have 2.0 mol $\text{N}_2$ and 4.0 mol $\text{H}_2$. Which reactant is limiting?

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