Fiveable
🧪AP Chemistry
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🧪AP Chemistry

FRQs 1–3 – Long Answer
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Unit 1: Atomic Structure and Properties
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FRQ Types & Units

Each FRQ type tests specific skills taught in particular units. Here's why certain units appear for each question type:

This mapping reflects College Board's exam structure - each FRQ type tests specific skills that are taught in particular units.

Practice FRQ 1 of 351/35
1. Answer the following questions about boron and its compounds.
Boron is a chemical element with atomic number 5. It exists naturally as two isotopes, boron-10 and boron-11.

Figure 1. Mass spectrum of boron (relative intensities of boron-10 and boron-11)

A single-panel vertical bar graph (mass spectrum) with a white background and no grid lines. Axes and scales: - Horizontal axis label centered below axis: "Mass Number (amu)". - The x-axis runs from 9 to 12 amu. - X-axis tick marks and tick labels appear at exactly: 9, 10, 11, 12. - Vertical axis label rotated along the left side: "Relative Intensity". - The y-axis runs from 0 to 100. - Y-axis tick marks and tick labels appear at exactly: 0, 25, 50, 75, 100. - Both axes end with arrowheads at the positive direction (right end of x-axis, top end of y-axis). Bars (two total, solid black fill, equal bar width): - Bar 1 is centered exactly above the x-axis tick labeled "10". The top of this bar aligns exactly with the y-axis tick labeled "25" (so the bar height is 25). - Bar 2 is centered exactly above the x-axis tick labeled "11". The top of this bar aligns exactly with the y-axis tick labeled "100" (so the bar height is 100). Spacing and alignment rules: - The two bars are separated by exactly one mass-number unit on the x-axis (from 10 to 11). - No other bars or peaks are present. - The baseline of both bars sits exactly on the x-axis at y=0. No legend and no additional annotations.
A. The mass spectrum of a sample of pure boron is shown in Figure 1.
i. Calculate the average atomic mass of boron based on the data in Figure 1. Show your work.
ii. Identify the number of neutrons in the nucleus of the most abundant isotope of boron.

Figure 2. Photoelectron spectrum (PES) of boron (binding energy vs. relative number of electrons)

A single-panel line graph of a photoelectron spectrum on a white background with no grid lines. Axes and orientation: - Horizontal axis label centered below the axis: "Binding Energy (MJ/mol)". - The x-axis uses a logarithmic scale and DECREASES from left to right. - The leftmost x-axis tick label is "100" and the rightmost x-axis tick label is "0.1". - The x-axis shows tick marks and labels at exactly these values, in decreasing order left to right: 100, 10, 1, 0.1. - Vertical axis label along the left side: "Relative Number of Electrons". - The y-axis runs from 0 at the bottom to 2 at the top. - The y-axis shows tick marks and labels at exactly: 0, 1, 2. - Both axes end with arrowheads at the positive direction (rightward for the drawn axis line and upward for y). (Even though binding energy decreases left-to-right, the axis line still has a right-end arrowhead.) Spectrum trace style: - A single continuous thin-to-medium solid black curve forms three narrow peaks. - Outside the peaks, the curve lies on (or essentially overlaps) the baseline at y=0. Exact peak positions and heights (three peaks total): - Peak A (highest-binding-energy peak) is placed in the left half of the plot between the 10 and 100 ticks, closer to the 10 tick than to the 100 tick, at a binding energy labeled by annotation text "19.3" placed directly below the apex. The apex height reaches exactly the y=2 tick mark. - Peak B (middle-binding-energy peak) is placed between the 1 and 10 ticks, closer to the 1 tick than to the 10 tick, at a binding energy labeled by annotation text "1.36" placed directly below the apex. The apex height reaches exactly the y=2 tick mark. - Peak C (lowest-binding-energy peak) is placed between the 0.1 and 1 ticks, closer to the 1 tick than to the 0.1 tick, at a binding energy labeled by annotation text "0.80" placed directly below the apex. The apex height reaches exactly the y=1 tick mark. Peak shapes and separation rules: - Each peak is a single smooth, symmetric bell-shaped bump (one apex per peak; no shoulders, no split peaks). - The three peaks do not overlap; the curve returns fully to the baseline (y=0) between each neighboring pair of peaks. No legend and no subshell labels are printed on the figure (only the three numeric binding-energy annotations at the peak apices).
B. The photoelectron spectrum (PES) of boron is shown in Figure 2.
i. Identify the subshell from which the electrons in the peak at 0.80 MJ/mol are removed.
ii. Predict whether the 1s peak in the PES of a carbon atom would be at a higher, lower, or equal binding energy compared to the 1s peak in Figure 2. Justify your answer using Coulomb's law and principles of atomic structure.
A student performs an experiment to determine the empirical formula of a boron hydride compound. The compound is heated in a crucible, decomposing it into solid boron and hydrogen gas. The data from the experiment are shown in Figure 3.

Figure 3. Decomposition data for boron hydride (masses recorded during heating)

A 2-column by 4-row data table with a single header row and three data rows. Black table borders; white cell backgrounds; left column text left-aligned, right column values right-aligned. Column headers (header row): - Column 1 header (top-left cell): "Measurement". - Column 2 header (top-right cell): "Mass (g)". Data rows (exact text in each cell): - Row 1: "Mass of empty crucible" | "25.000" - Row 2: "Mass of crucible + boron hydride" | "26.500" - Row 3: "Mass of crucible + boron residue" | "26.172"
C. Using the data in Figure 3, calculate the number of moles of hydrogen gas lost during the decomposition.
D. Using your answer from part C and the data in Figure 3, determine the empirical formula of the boron hydride compound. Show your work.
E. The student hypothesizes that the sample of boron hydride was contaminated with water, which evaporated along with the hydrogen during heating. If this hypothesis is correct, would the calculated mass percent of hydrogen in the compound be greater than, less than, or equal to the actual mass percent of hydrogen? Justify your answer.
F. Boron and aluminum are in the same group on the periodic table.
i. Explain why the atomic radius of aluminum is larger than the atomic radius of boron.
ii. Explain why the first ionization energy of aluminum is lower than the first ionization energy of boron.
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FRQ Directions
Free Response Question Practice

This practice environment simulates the AP AP Chemistry Free Response Questions section. Here are some guidelines:

  • Read each question carefully before responding. Pay attention to command verbs like "identify," "explain," "analyze," or "evaluate."
  • Use the timer to practice time management. You can pause, restart, or hide the timer as needed.
  • Mark for Review if you want to come back to a question later.
  • Your responses are saved automatically as you type. You can also use the drawing tool for questions that require diagrams or graphs.
  • Use the toolbar for formatting options like bold, italic, subscript, and superscript.
  • Navigate between questions using the Previous and Next buttons at the bottom of the screen.

Tip: Answer all parts of each question. Partial credit is often available, so even if you are unsure, provide what you know.