A scientist is analyzing a pure sample of Element Z to determine its atomic structure and properties. The scientist obtains the photoelectron spectrum (PES) shown in Figure 1 and the isotopic data shown in Table 1.
Table 1. Isotopic data for Element Z
Isotope
Isotopic Mass (amu)
Relative Abundance (%)
Z-24
23.99
79.00
Z-25
24.99
10.00
Z-26
25.98
11.00
Figure 1. Photoelectron spectrum (PES) of Element Z
A.
On the PES diagram in Figure 1, circle the peak corresponding to the valence electrons of Element Z.
B.
i.
Calculate the average atomic mass of Element Z using the data in Table 1.
ii.
Using your answer to part B(i), calculate the number of atoms in a 3.50 g sample of Element Z.
C.
Explain why the first ionization energy of Element Z is greater than the first ionization energy of Sodium (Na), which is the element directly to the left of Element Z in the periodic table. Element Z is located in the third period of the periodic table.
What the FRQ 7 Short Answer asks
FRQ 7 is the last of four short-answer questions on the AP Chemistry exam, worth 4 points and focused on one topic. In this set, you circle a feature on a diagram, work two linked calculations, then explain a result.
Usually, mark a feature on a figure, like an atom or an electrode
1 pt
B
Part B: Two calculations
A calculation, then a second one that uses its answer
2 pts
C
Part C: Explain
A prediction or comparison, with the chemical reason
1 pt
How FRQ 7 Short Answer practice works
Each question follows the exam’s format, from the full prompt to a score on every part.
1
Read the full question
The setup, the figure or data table, and every part, laid out the way the exam shows them.
2
Write on a 9-minute timer
A pace that fits all seven questions into the 105-minute section. Pause it or turn it off, and your response saves as you go.
3
Submit for a score out of 4
Your response is scored against the scoring guidelines written for that question. Your first score is included.
Feedback on every part
A summary at the top tells you what to work on next. Below it, each part shows whether you earned the point and what the scoring guidelines were looking for.
Did not earn the point. You circled the oxygen atom instead of the nitrogen atom. To earn the point, you needed to circle the nitrogen atom, which has a lone pair that is more available to accept a proton when hydroxylamine acts as a base.
Part B(i): 1/1 point
Earned the point. You correctly calculated the value of Kb as 1.13x10^-8.
Part C: 1/1 point
Earned the point. You correctly agreed with the claim and justified it by explaining that the hydronium ion is present at the start and end of the reaction, which shows it is consumed and then regenerated.
Detailed feedback on a practice FRQ 7 Short Answer
Questions about the FRQ 7 Short Answer
How many responses can I get scored?
You can read every question without a plan. Your first scored response is included. A plan unlocks unlimited scoring.
What if I can’t finish the first calculation in part B?
Use a reasonable value, say where it came from, and work the second calculation. Each of the two steps has its own point.
How do I type formulas, charges, and drawings?
Use the subscript and superscript buttons for formulas and ion charges. For a drawing, like a Lewis diagram or a mark on a figure, use the drawing tool, or switch the editor to handwrite, draw on paper, and add a photo of your page.
How are short-answer questions different from FRQs 1 to 3?
Short answers are 4 points and stay on one topic, usually with one point per scored step. FRQs 1 to 3 are 10-point problems with about six parts.
Can I use a calculator and the equations sheet?
Yes. The practice screen has a calculator and the AP Chemistry equations sheet with the periodic table, which you also get on exam day.
More AP Chemistry practice
FRQ 1 Long Answer practice
FRQ 1 long-answer questions with every part, figure, and data table.
