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How to Ace Your AP Chemistry Labs

Posted by Samantha Lindsay | Apr 6, 2016 8:00:00 PM

Advanced Placement (AP)

 

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Labs play a significant role in AP Chemistry, and knowledge of experimental procedures is critical for the final exam. If you're an AP Chemistry student (or are considering becoming one), this guide will help you understand what to expect from the lab components of the course.

I'll provide an overview of the types of AP Chemistry labs you'll see, the amount of time you'll spend on them, and what a real lab procedure looks like. You'll also learn how lab reports are structured and what you can do during the lab to ensure that you're getting the most out of your experience!

 

What Are the Lab Requirements for AP Chemistry?

Twenty-five percent of class time in AP Chemistry is devoted to labs, so they’re a big part of the course. The College Board even says in the course description that increased lab time is correlated with higher AP scores! You will be expected to conduct at least sixteen hands-on lab experiments throughout the year, and at least six of those sixteen must be "guided inquiry" labs. 

The College Board emphasizes an inquiry-based approach in the most up to date curriculum guidelines for AP Chemistry. This means that you’ll be asked to work independently at times. The teacher will provide a prompt or question, but you'll design the rest of the lab. This gives you the opportunity to conduct valid experiments that test your hypotheses without a teacher holding your hand the whole way. 

This approach is geared towards helping students develop scientific skill sets that they will use later in life when there isn't a teacher around to give them the answers.

In guided inquiry labs, you will be expected to:

  • Come up with a scientific question
  • Decide which variables you will investigate
  • Design and conduct experimental procedures
  • Collect, analyze, interpret, and display data
  • Present conclusions appropriately

 The other (up to) ten labs in the course may be traditional teacher-directed labs, but they will still support the learning objectives of the course. A full list of AP Chemistry learning objectives divided by the main themes or “Big Ideas” can be found on page 107 of the course guidelines. The goal for each lab is to incorporate as many of these objectives as possible so that students get the most out of their time. Each lab will serve a purpose in helping you grasp essential concepts in AP Chemistry.



Which AP Chemistry Labs Will You Actually Have to Do?

The AP Chemistry lab curriculum offers a fair amount of flexibility. The College Board provides a lab manual to teachers that includes 16 guided inquiry labs. Teachers can then choose at least six of those labs to conduct in class. The other ten or more labs in the course may be teacher-directed (traditional, step-by-step labs where all students follow one exact procedure).

 

Examples of lab topics you might explore in AP Chemistry include:

  • Spectroscopy
    • Determine the concentration of a solute in solution based on the color of the solution
  • Gravimetric Analysis of a Precipitate
    • Find the identity of an unknown compound using mass data
  • Stoichiometry
    • Determine the amount of dissolved particles present in solution
  • Solubility
    • Determine the amount of dissolved ions in solution
  • Redox Titration
    • Measure the amount of acid contained in a solution
  • Reaction Rate
    • Manipulating variables to see how they affect chemical reaction rates
  • Energy
    • Determine change in energy in various chemical reactions
  • Equilibrium
    • Maximizing yield in chemical reactions
  • Weak Acid Titration
    • Drawing conclusions about acid properties from a pH titration curve for a weak acid
  • Buffers
    • Explore how buffers are made and what determines their capacity to resist changes in pH
  • Electrochemistry
    • Using electrolysis to induce non-spontaneous chemical reactions

 

body_eplore.jpgGet ready to explore the fascinating and terrifying landscape of microscopic particles that make up our world.

 

AP Chemistry Lab Example

Here’s a more specific example of an AP Chemistry Lab. In this case, it was derived from the AP Chemistry Lab Manual, so it’s an inquiry-based lab. 

 

Lab Title: 

The Preparation and Testing of an Effective Buffer: How Do Components Influence a Buffer's pH and Capacity?”

 

Experiment Overview:

In this experiment, the pH of water and a number of other solutions will be measured, and then acids and bases will be added to see how the pH is affected.  Several buffer solutions of different pH values will be prepared and tested for their ability to resist change in pH.

This covers the following AP Chemistry learning objective (LO 6.18):
The student can design a buffer solution with a target pH and buffer capacity by selecting an appropriate conjugate acid-base pair and estimating the concentration needed to achieve the desired capacity.

 

Materials Needed:

  • Hardware:
    • Balance with 0.01-gram precision
    • Four 100 mL beakers
    • Three pipets
    • Buret, ring stand, buret clamp
    • Two 250 mL Erlenmeyer flasks
    • Two graduated cylinders, 25 mL and 100 mL
    • pH meter
    • Stirring rod
    • Wash bottle and distilled water
  • Chemical Solutions:
    • 20 mL Acetic acid, 0.10 M
    • 20 mL ammonia, 0.10 M
    • 20 mL ammonium chloride, 0.10 M
    • 5 mL HCl, 0.10 M
    • 1 mL of 1 percent Phenolphthalein
    • 20 mL sodium acetate, 0.10 M
    • 40 mL sodium chloride, 0.10 M
    • 5 mL sodium hydroxide, 0.10 M
    • Unknown solid acid sample, 2.0 g

 

Safety Precautions (an extremely important part of each lab, especially when you’re dealing with strong acids!):

Wear chemical splash goggles, chemical resistant gloves, and a chemical resistant apron.  Wash hands thoroughly with soap and water before leaving the laboratory.

 

Procedure:

Part 1: pH Changes in Non-buffered Solutions

1. Place 20 mL of distilled or deionized water in a 100 mL beaker. Test the pH using a pH meter. Record the pH.
2. Using a pipet, add one drop of 0.10 M HCl, stir the solution and again test and record the pH.
3. Repeat step 2 with a second and third drop of 0.10 M HCl.
4. Repeat steps 1-3 with 20 mL of 0.10 M NaCl solution.
5. Place 20 mL of distilled or deionized water in a 100 mL beaker. Test the pH using a pH meter. Record the pH.
6. Using a pipet, add one drop of 0.10 M NaOH, stir the solution and again test the pH and record.
7. Repeat step 6 with a second and third drop of 0.10 M NaOH.
8. Repeat steps 5-7 with 20 mL of 0.10 M NaCl solution.

 

Part 2: pH Changes in Buffered Solutions

9. To prepare a buffer, use 25 mL graduated cylinder to add 10 mL of 0.10 M HC2H3O2 and 10.0 mL of 0.10 M NaC2H3O2 to a 100 mL beaker.
10. Measure the pH of the buffer solution and record.
11. Add 1 drop of 0.10 M HCl, stir, measure and record the pH.
12. Repeat step 11 for two additional drops of 0.10 M HCl.
13. Prepare a fresh sample of the HC2H3O2 - C2H3O2- buffer as in step 9.
14. Repeat steps 11 and 12 by adding 0.10 M NaOH.
15. Prepare a basic buffer by combining 10.0 mL of 0.10 M NH3 and 10.0 mL of 0.10 M NH4Cl in a 100 mL beaker.
16. Repeat steps 11 and 12 for this basic buffer solution.
17. Repeat step 14 by preparing a fresh sample of the basic buffer and testing it with a dropwise addition of three drops of 0.10 M NaOH.

 

Part 3: Preparation of Buffer of a Given pH

18. Weigh out 1.8 to 2.0 g of a solid acid assigned to you.
19. Dissolve the acid in 150 mL of distilled water in a 250 mL Erlenmeyer flask (flask 1).
20. Pour 75 mL of this solution into a second 250 mL Erlenmeyer flask (flask 2), add 2 drops of phenolphthalein solution, and titrate to the phenolphthalein color change with 0.20 M NaOH. Record the volume of titrant. You now have a solution of a weak acid in flask 1, and a solution of the sodium salt of the weak acid (its conjugate base) in the second flask 2. Make the concentrations of the two solutions the same by adding the same volume of distilled water to the acid flask 1 as the volume of NaOH you used to titrate the solution in flask 2.
21. Combine 10.0 mL of your weak acid solution in flask 1 with 10.0 mL of the conjugate base solution in flask 2, mix, and measure the pH and record.  This is the pKa of the acid.
22. Your teacher will assign you the pH of a buffer to prepare.  Calculate the volume of weak acid and conjugate base that you will need to prepare 50 mL of a buffer of the assigned pH.
23. Measure out the volumes of acid and conjugate base, mix then measure and record the pH.
24.Test your buffer solution to see if it resists changes in pH by measuring 20.0 mL of the and adding 3 drops of 0.10 M HCl, and repeating with 20.0 mL of buffer and 3 drops of NaOH.  Record the pH values after each addition.

 

Conclusion Questions:

1. Discuss how the addition of acid and base to distilled water affected its pH.
2. Discuss how the addition of acid and base to 0.10 M NaCl solution affected its pH.
3. Discuss how the addition of acid and base to the acetic acid-acetate ion buffer affected the pH.
4. Discuss how the addition of acid and base to the ammonia-ammonium ion buffer affected the pH.
5. Did your prepared buffer match your assigned pH value? Explain.
6. Comment on the ability of your prepared buffer to resist the change of pH when acid and base were added in the last step of the investigation. 

 

Notice that this lab ultimately requires independent problem-solving skills on the part of the student. You must create your own buffer solution of a certain pH and then test it to see if it’s effective. While the procedure is clearly laid out, it won’t be exactly the same for each person. You could come up with more than one way to make the final buffer solution for any given pH, so the lab is flexible depending on how you think about the problem. This type of lab encourages you to use knowledge of chemistry to solve a problem creatively.

 

body_puzzlepieces.jpgAll the pieces of the puzzle are there for guided inquiry labs, but you're responsible for putting them together! You'd better hope it's not one of those puzzles with a million blue sky pieces that all look the same.

 

How Are Lab Reports Structured?

Ah, lab reports, the not-so-fun part of playing with chemicals. Lab reports might seem daunting, but if you conduct the experiment properly and prepare some parts of your report beforehand, you should be fine. I took the lab guidelines below from a sample syllabus provided by the College Board. It lists ten essential components of an AP Chemistry lab report and shows when each should be completed (before, during, or after the lab is conducted).

Your teacher may have slightly different expectations (sometimes you have to list the materials needed for the lab before the procedure, for example), and even those will change slightly depending on the nature of the lab. These are just the components of a standard chemistry lab report to give you an idea of what to expect! 

 

To Set Up Your Lab Report, You Will:

1. Write an accurate descriptive title for the lab (i.e. pH Titration Lab)
2. Write the date of the lab
3. Provide a purpose statement explaining the point of the lab
4. Write an outline of the lab procedure (often this is in bullet-point form)
5. Answer any pre-lab questions
6. Create data tables that you’ll fill in during the lab

 

During the Lab You Will:

7. Record data from the experiment in a neat, well-organized fashion

 

After the Lab You Will:

8. Show calculations and draw out any corresponding graphs (be sure to label everything correctly!)
9. Write a conclusion about your findings (format may vary depending on the lab)
10. Answer post-lab error analysis questions

 

Note that you should always write these reports in the 3rd person (i.e. "the solution was titrated" rather than "I titrated the solution"). Lab reports are intended to be objective statements of the facts, so “I” or “We” statements will just make them seem less credible!



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Always use the third person in scientific writing. I mean, look at that dude. He clearly knows way more about chemistry than those other two schmucks.

 

Tips for AP Chemistry Labs

Here are some essential tips you should keep in mind during AP Chemistry labs. They'll save you from wasting your time in class and turning in a crappy lab report!  

 

Tip #1: Don’t Get Careless

If you’re tired or just not feelin’ chemistry one day, the last thing you want to hear is that you’re expected to get out of your chair and do a lab. On those occasions, try to summon your remaining strength to get through the class. If you don’t do a lab correctly the first time, you’ll be in for a lot of trouble when you try to write your report.

You know a movie is going to be bad if the director has to say “we’ll fix it in post-production.” Similarly, if you mess up during the actual experiment, don’t think “eh - I’ll just fix it in the lab report.” You should do things correctly so that you don’t get the wrong impression of how the lab was conducted and end up struggling on your next test (or handing in data that makes no sense). Redo everything the right way before moving forward!

 

Tip #2: Record Everything Clearly (and Don’t Fudge the Data Later)

The most critical part of each lab is data collection. It would be tough to forget to write down all of your data, but sometimes you can end up writing illegibly or organizing results in a way that won’t make sense to you later. Carefully lay out your data tables before starting the experiment so that you have a designated place to record results. Try to write clearly and neatly so there’s no chance of misunderstandings. 

If your data doesn’t fit with your hypothesis of how the lab was supposed to go, write it down anyways (as long as you don’t think you made any big mistakes in following the procedure). You’ll be able to discuss why your data was wonky in the conclusion section of the report. Don’t get in the habit of faking results - it makes the experiment pointless.

 

Tip #3: Ask for Clarification if Necessary 

Your teacher is there to help you, so don’t be afraid to use him or her as a resource! If, at any point during the lab, you’re not sure whether you’re conducting the procedure correctly, you should check in with your teacher to verify. This will prevent the nightmare scenario of sitting down to write a lab report and realizing you essentially did a completely different lab and have no usable data. 

 

body_scaryforest.jpgEveryone has the same nightmare when they follow the wrong lab procedure: You're walking through a gloomy forest when suddenly you sense that you're being watched. You hear a haunting whisper, "I tooooold you to use 20 ml of HClllll." You wake up in a cold sweat as you're about to be sacrificed over a Bunsen burner by a coven of AP Chemistry teachers.

 

Conclusion

AP Chemistry is a fairly lab-centric course, so you should be prepared to spend a lot of time doing hands-on experiments (at least 25 percent of the class!). The lab requirements are open to some interpretation, but, per the curriculum guidelines, courses must include at least 16 labs total, at least six of which are special "guided inquiry" labs. These are independently-conducted labs where students have greater agency over the procedure and outcome.

 

When conducting labs, you should keep the following tips in mind:

1. Don't Get Careless
2. Record Everything Clearly, and Don't Fudge the Data Later
3. Ask Your Teacher for Clarification if Necessary

 

Adhering to these tips will make the process of writing a lab report relatively painless later. If you conduct the experiment correctly and have solid data, the only part of the report that you'll need to worry about is the conclusion.  

The goal of all this lab work is to teach you to apply sound scientific practices across a variety of circumstances. Many questions on the final exam will ask you to analyze experimental scenarios based on your knowledge of lab procedure and chemical properties. In some cases, you might even recognize experiments from class! 

 

What's Next?

If you're kind of nervous about taking AP Chemistry, take a look at my article analyzing the difficulty level of the course across five different metrics. 

Are you looking for a good review book? Check out my list of the best AP Chemistry review books available for students this year!

Still working on planning out your schedule? Learn more about which science classes you should take in high school.

 

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Samantha Lindsay
About the Author

Samantha is a blog content writer for PrepScholar. Her goal is to help students adopt a less stressful view of standardized testing and other academic challenges through her articles. Samantha is also passionate about art and graduated with honors from Dartmouth College as a Studio Art major in 2014. In high school, she earned a 2400 on the SAT, 5's on all seven of her AP tests, and was named a National Merit Scholar.



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