Practice Test 26 - High School Chemistry

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

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1. In a nuclear power plant, a uranium nucleus absorbs a neutron and then splits into two smaller nuclei, releasing several neutrons and a large amount of energy. Which type of nuclear process is described?
2. A student mixes 10 mL of vinegar (aqueous acetic acid) with 2.0 g of baking soda (sodium bicarbonate, $\text{NaHCO}_3$) in a flask and quickly places a balloon over the opening. Observations and data: - Immediate vigorous fizzing - Balloon inflates over 30 seconds - Temperature: $24.0^\circ\text{C}$ before, $20.5^\circ\text{C}$ after 1 minute - After fizzing stops, the liquid is clear with no solid remaining Did a chemical reaction occur? Choose the best CER justification.
3. A student adds 5.0 g of table salt (NaCl) to 100 mL of water at 20.0°C and stirs for 2 minutes. The salt "disappears," and the solution remains clear. The cup feels slightly colder. After stirring, the temperature is 18.8°C. The student then pours the solution into a shallow dish and leaves it overnight; the next day, white crystals are present in the dish. Did a chemical reaction occur when the salt was added to the water? Choose the best CER justification.
4. Calcium carbonate decomposes according to: $\textbf{CaCO}_3 \rightarrow \textbf{CaO} + \textbf{CO}_2$ If $2.25\ \text{mol}$ of $\text{CaCO}_3$ decompose completely, how many moles of $\text{CO}_2$ are produced?
5. Neon has electron configuration [He]2s2 2p6 and sodium has electron configuration [Ne]3s1. Neon has a much higher first ionization energy than sodium. Which explanation best uses electron configuration to explain this difference?
6. Lithium (Li) is a group 1 element with atomic number 3. It commonly forms Li. Which option correctly explains what changes when Li becomes Li?
7. Calcium (Ca) has atomic number 20. What is the correct electron configuration for a neutral calcium atom (fill through 4s as needed)?​
8. Two clear, colorless liquids are poured together in a beaker. Within seconds, the mixture turns cloudy and a white solid appears and settles to the bottom. Which observation best indicates that new substances formed?
9. An instant cold pack works because a salt dissolves in water and the process has $\Delta H = +25\ \mathrm{kJ}$. What should happen to the temperature of the surroundings (your hand holding the pack) when it is activated?
10. 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?
11. A maker-space uses "instant cold packs" for minor injuries. Someone suggests making a reusable version by mixing ammonium chloride with water in a sealed bag, but they are unsure whether the process is a chemical change or just dissolving. Which investigation design best tests whether mixing ammonium chloride with water causes a chemical change, using observable evidence and a control?
12. A student designed a reusable water bottle with a metal interior coating. The coating was chosen to prevent metallic taste and to protect the metal from corrosion. After 6 weeks of use with sports drinks (acidic, pH around 3–4), users reported a metallic taste, and inspection showed small blisters and peeling of the interior coating near the bottom seam. Which refinement best follows from the evidence?
13. In a single-step reaction energy diagram (energy vs reaction progress), the reactants are at 60 kJ and the products are at 90 kJ. What does this indicate about the overall energy change $\Delta H$?
14. The ion $\,^{23}\mathrm{Na}^{+}$ (sodium-23 with a +1 charge) is given. How many protons, neutrons, and electrons does this ion have?
15. A student leaves an ice cube on a plate in a warm room. After 10 minutes, the ice cube has turned into a puddle of liquid water. Which type of change is described?
16. In methane combustion, $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$, C–H and O=O bonds are broken and C=O and O–H bonds form. Which statement best describes the overall energy change in terms of bonds?
17. A science class is choosing a material for a small beaker used to heat a salt solution on a hot plate to near boiling. Requirements: (1) must tolerate high temperature without melting/warping (critical), (2) should not react with the salt solution, and (3) should be reasonably safe and affordable. Options: - Borosilicate glass: excellent heat resistance; chemically inert for salt solutions; breakable if dropped. - Polyethylene plastic: cheap; chemically resistant; but softens/melts at relatively low temperatures. - Aluminum cup: conducts heat well; won't melt at these temperatures; but can react/corrode with some solutions over time and may contaminate contents. Which material is the best trade-off for this heating application?
18. Two students debate whether a reaction occurred when 3.0 g of a drink mix powder was stirred into 100 mL of water. Observations: - The powder dissolves; no solid remains after stirring. - The solution changes from colorless to bright orange. - The temperature changes from $21.8^\circ\text{C}$ to $21.7^\circ\text{C}$. - The orange color becomes lighter if more water is added. Which CER justification best evaluates whether there is sufficient evidence that a chemical reaction occurred?
19. Melting ice is represented by: $\mathrm{H_2O(s) \rightarrow H_2O(l)}$ $\Delta H = +6.0\ \mathrm{kJ/mol}$ Which statement is correct?
20. A student compared the reactivity of three metals with $1.0\,\text{M}$ HCl at $22.0^\circ\text{C}$. Each metal sample had a mass of $0.50\,\text{g}$. The student recorded time to visible bubbling and qualitative observations.

    Metal	Time to first bubbles (s)	Bubbling intensity (first 30 s)
    Mg	2 s	vigorous
    Zn	12 s	moderate
    Cu	no bubbles after 120 s	none

    Which statement best describes the pattern in the data?​

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