FRQ practice is one of the most important ways to prepare for the AP Chemistry exam! Review these students' responses to a unit 1 practice prompt focused on photoelectron spectroscopy - all with corresponding feedback from Fiveable teacher Wes Winter! 

Consider the following photoelectron spectroscopy data:

a) Based on the graph, identify the element and write the full electron configuration.
b) A student claims that the 1s peak for sulfur (S) would be further to the right than the 1s peak of this element. Is this student correct? Justify your answer.

b)This student is incorrect because the distance between the 1s orbital and the nucleus for a sulfur atom is less than the distance for a silicon atom due to the increased number of protons in sulfur that allow for a strong attraction and hold on the inner electrons. This means that more energy would be required for an s orbital electron to be removed and the 1s peak would be further left than the 1s peak for Silicon.

I think the only change would be referencing the attractive force to the electrons to the nucleus, not the distance (Though true). A better statement would sound "Since sulfur has more protons than silicon, Sulfur has a greater nuclear charge, thus a greater attraction to the 1s electrons.
Nice!

a) Silicon is the element. The electron configuration is: [Ne] 3s^2 3p^2.

b) The student is incorrect - the 1’st peak for sulfur would NOT be further to the right than the 1st peak for silicon. This is because sulfur has a smaller atomic radius and a higher electronegativity than silicon. All of these factors would result in a higher amount of energy required for sulfur in the photo electra spectra because sulfur has greater attractions to the nucleus compared to silicon, making it harder for electrons to be removed.

Your statement in regards to 1b) is correct, however your justification is off. What can be frustrating about this section is when to use which justification. 

The biggest reason that the 1s peak for sulfur would be further to the left is because the nuclear charge (number of protons) for sulfur is greater.

 While your other statements are true, they do not correctly justify the location of the 1s peak. Hope this helps.

a) The element is silicon. It has an electron configuration of 1s22s22p63s23p2
b) This student is incorrect. The 1s peak for sulfur would be further to the left on the photoelectron spectra. This is due to the fact that sulfur has more protons in the nucleus and therefore has a greater nuclear charge. This greater positive charge attracts the electrons in sulfur greater, thus moving the peak further to the left.



AP Chemistry Exam

AP Chemistry Review 2020 | Examp Prep +  Free Practice | Fiveable

AP Chemistry

Free Reviews 2020

Free Response Questions

Unit 1: Atomic Structure and Properties

Unit 2: Molecular and Ionic Compound Structures and Properties

Unit 3: Intermolecular Forces and Properties

Unit 4: Chemical Reactions

Unit 5: Kinetics

Unit 6: Thermodynamics

Unit 7: Equilibrium

Unit 8: Acids and Bases

Unit 9: Applications of Thermodynamics

Introduction

AP Chemistry Essentials

Multiple Choice Questions

Blogs

Big Reviews: Finals & Exam Prep

Q and A sessions

Test

Live Cram Sessions 2020

AP Chem Unit 1 FRQ Practice Prompt Answers & Feedback

The written response section or Free Response Questions of the AP Chemistry is the second and final section of the AP Chemistry exam. The FRQs are designed to test the 6 major concepts covered throughout the AP Chemistry Course:

The FRQs will also cover other important concepts such as experimental design and analysis of lab data and observations and will also look for a logical path towards your answer. There are 7 FRQs on the exam: 3 long answer questions and 4 short answer questions (we will break down the specifics of these two types of questions in a later section). All questions are multi-step questions and will test a variety of topics and skills learned throughout the AP Chemistry course. 

For more info about these key concepts & skills straight from the College Board click 

As you know, the FRQ section on the AP Chem exam is 7 questions long (3 long, 4 short answer questions). You will have 1 hour and 45 minutes to complete the section. Your score on this section equates to 50% of your total exam score. Here is a clip of 

, a chemistry streamer, going over the format of the exam as a whole.

The short answer questions are single or multi-part questions that are scored out of a total of 4 points. The long answer questions are always multi-part and are worth a total of 10 points. A good breakdown of time for these questions would be:

Here are the task verbs for the chemistry FRQ:

Read each part of the question from top to bottom or bottom to top. Make sure you understand what each part of the question is asking before moving on. 

Figure out your plan of attack. Make a list of any given information and call to mind the skills you need to apply to answer the problem. Determine if calculations are needed or if you have to draw a diagram. Also, look out for questions asking you to “prove” or “justify” your answer and then think about any theoretical topics you’ve learned that will help you validate your answer. 

This is your time to shine! Use the information you have already organized to move through each problem. Apply all skills and perform all calculations. Make sure to answer all parts of the question and to justify your answer whether it be with a calculation, a rule/law, a trend, or theory.  Make sure to reference both substances in your justification/explanation.

Make sure you’ve answered everything. Are your units and/or the number of significant figures correct? Have you missed anything? Are your calculations accurate? Walk through each step of the problem and connect it to how you got your answer. 

Remember, you got this! Image Courtesy of 

Write with precision and confidence. Convey your answer clearly and accurately--nothing more, nothing less. Don’t distract your reader with rambling or long-winded explanations and make sure to use proper grammar. 

Be careful to make sure all of your answers make logical sense and “add up” as you work from part 1 to the end of the problem

In other words, maximize your credit on each problem. If a question has multiple answers make sure you select the best one. Always be sure to prove or justify your answer if applicable. You may get partial credit for any question so if you have any knowledge for any part of a question include it! 

Sounds silly, but always be sure to accurately label your work. Make certain you correctly use terminology (ie. molecule, ion, mol, bond, atom, attraction, force, etc.)  and symbols (ie. k,  K, M, m, etc.) 

It is super helpful to understand the major concepts and most important topics of Chemistry when trying to answer FRQs efficiently. Develop a good foundation with all of these but specifically 

 (as recommended by the College Board). Also, knowing your significant figures rules and conversion factors will boost your chances of getting every point possible! 

A student is performing an experiment with NO2(g). The gas is in a rigid container, originally at 300. K and 2.0 atm. The student increases the temperature of the gas to 450 K. 

       Describe the effect of raising the temperature of NO2(g) on the movement of the NO2(g) molecules. 

       Calculate the pressure in the container at 450 K. 

       Use the Kinetic Molecular Theory to explain why the pressure of NO2(g) changes when the temperature is   increased.  

       The student measures the actual pressure of NO2(g) in the container and sees it is less than the pressure predicted by the ideal gas law. Explain why this occurred. 

The question includes information about a sample of gas & there are 4 questions to answer. 

 Remember the Kinetic Molecular Theory and the Ideal Gas Law. Most gas questions can be broken down to those two concepts.

 As temperature increases, the gas molecules have a higher average amount of kinetic energy and move with a greater velocity. As a result, the pressure increases in a rigid container. The particles collide with the container walls with a greater amount of force.

. Use PV = nRT to calculate the new pressure at the higher temperature. All variables remain constant except pressure and temperature. Simplify down to 

(2.0 atm / 300. K) = ( P2 / 450. K)    

 According to the Kinetic Molecular Theory, the average kinetic energy of a sample of gas particles is directly proportional to the kelvin temperature. When the temperature of the gas sample is increased, the average kinetic energy also increased, resulting in a greater velocity. This resulted in a greater pressure at the increased temperature, since the number of collisions the molecules have with the walls of the container increased. 

 The real gas pressure is less than ideal gas pressure due to attractive forces between the NO2 gas particles. The NO2 molecule is polar and exerts attractive forces resulting in a lower gas pressure due to less molecules colliding with the container’s walls. 

See below for a quick breakdown of each point. 

1 point comes from correctly relating temperature to gas motion.

1 point comes from correctly calculating P2.

 the relationship between Kinetic Molecular Theory to pressure and temperature.

1 point comes from correctly explaining the causes of “real” gas pressure.

Here is an example of the process described above for answering a free-response question. This is a long answer question, but the steps taken to answer all FRQs should be relatively the same. Begin by completing a thorough

1. Answer the following questions regarding the photoelectron spectra for calcium and potassium.

A. On the PES spectra above write an X above calcium’s valence electrons. Justify your answer using Coulomb’s Law.

B. Explain WHY every peak for calcium is shifted slightly to the left of potassium.

C. Would the peaks for an ion of calcium (Ca2+) be shifted to the left, right or stay the same as the peaks of the calcium atom shown in the diagram?  Justify your answer.

D. Would the photoelectron spectra of 39K and 40K be the same or different?  If they were different, in what way(s)?  If they were the same, why?  Justify your answer.

The question includes 2 PES graphs & there are 5 questions to answer. 

I have to draw an “X” above the peak that represents the valence electrons for calcium and use Coulomb’s Law to justify my answer. 

1A. The ‘X’ should be above the purple peak just to the right of 1 MJ/mol. This peak represents the valence electrons for calcium. The height equals 2 electrons and the position at the lowest binding energy means that those electrons are held onto with the least amount of energy. Using Coulomb’s law, the valence electrons are the furthest away from the nucleus and have the weakest interaction. There is significant shielding between the valence electrons and the nucleus resulting in the lowest binding energy. As the distance increases the energy decreases (inverse square relationship).

1B. Calcium has a higher effective nuclear charge than potassium, as a result the electrons are more tightly held than potassium’s electrons. This results in every electron in calcium having a slightly higher binding energy than the electrons in potassium.

1C. Stay the same, however, the peak for the valence electrons (the rightmost peak) would be missing. Both the calcium ion and calcium atom have the same effective nuclear pull, therefore the binding energy would be the same.  

1D. The PES spectra of the potassium isotopes would be the same. Both isotopes have the same number of protons, resulting in the same effective nuclear pull and the same binding energies for electrons in the electron clouds. Isotopes differ in number of neutrons which is irrelevant when discussing binding energies (ionization energies).

1Eb. 3d1 This peak only has 1 electron and is filled after 4s2. It has slightly higher binding energy suggesting that it is NOT a valence energy level electron, this puts it in energy level 3. 

The exact source of points in an AP Chemistry FRQ differs on a problem to problem basis, but you will always get the points for the correct answer. However, the correct answer is not always the only point to scoop up for any given question. Points will often come from correct explanations, units, secondary calculations, or balancing an equation. You may also earn partial credit on FRQ problems for answers that follow the correct approach but have the wrong numeric answer or answers that have some but not all parts of the correct answer. 

1 point comes from correctly naming the location of the “X” AND 1 point for using Coulomb’s Law (effective nuclear charge) to

 the answer. See why justification and proving your answer is important? 

1 point comes from correctly justifying the location of calcium’s peaks.

AP Chemistry Free Response Questions

Free 2020 ACT Test Prep | Video Reviews + Study Tips | Fiveable

Reading

Writing

Math

Science

Essay

First Unit

AP Art History Exam

AP Art History Exam Prep 2020 | Reviews + Free Study Help | Fiveable

AP Art History

Free Reviews

Unit 1: Global Prehistory, 30,000–500 bce

Unit 2: Ancient Mediterranean, 3500 bce–300 ce 

Unit 3: Early Europe and Colonial Americas, 200–1750 ce 

Join our Discord

Free Response Questions

AP Chemistry

all

study guides

blogs

browse by units

Free Reviews 2020

Free Response Questions

Unit 1: Atomic Structure and Properties

Unit 2: Molecular and Ionic Compound Structures and Properties

Unit 3: Intermolecular Forces and Properties

Unit 4: Chemical Reactions

Unit 5: Kinetics

Unit 6: Thermodynamics

Unit 7: Equilibrium

Unit 8: Acids and Bases

Introduction

AP Chemistry Essentials

Multiple Choice Questions

Blogs

Join Our Discord

Free Response Questions

AP Chemistry

all

study guides

blogs

browse by units

Free Reviews 2020﻿

Free Response Questions﻿

Unit 1: Atomic Structure and Properties﻿

Unit 2: Molecular and Ionic Compound Structures and Properties﻿

Unit 3: Intermolecular Forces and Properties﻿

Unit 4: Chemical Reactions﻿

Unit 5: Kinetics﻿

Unit 6: Thermodynamics﻿

Unit 7: Equilibrium﻿

Unit 8: Acids and Bases﻿

Introduction﻿

AP Chemistry Essentials﻿

Multiple Choice Questions﻿

Blogs﻿

Join Our Discord

Free Reviews 2020

Free Response Questions

Unit 1: Atomic Structure and Properties

Unit 2: Molecular and Ionic Compound Structures and Properties

Unit 3: Intermolecular Forces and Properties

Unit 4: Chemical Reactions

Unit 5: Kinetics

Unit 6: Thermodynamics

Unit 7: Equilibrium

Unit 8: Acids and Bases

Introduction

AP Chemistry Essentials

Multiple Choice Questions

Blogs