AP Chemistry Lab InvestigationsAll 16 Required Investigations

The 13 required AP Chemistry lab investigations

1. 1

   What is the Relationship between the Concentration of a Solution and the Amount of Transmitted Light through the Solution?

   Unit 3 · Properties of Substances and Mixtures

   Students prepare a series of known copper sulfate solutions at varying concentrations, measure the absorbance of each using a colorimeter or spectrophotometer, and construct a calibration curve to verify the Beer Lambert law relationship. The core finding is that absorbance is directly proportional to concentration when the path length and wavelength are held constant, making it possible to determine the concentration of an unknown solution from a measured absorbance. This investigation develops four skills central to AP Chemistry: preparing standard solutions by serial dilution, operating optical measurement instrumentation, constructing and interpreting a best fit linear calibration curve, and using Beer Lambert quantitatively to solve for an unknown. The investigation also introduces systematic error analysis, asking students to identify which variables most affect the linearity of the calibration and how instrument selection or operator technique could introduce deviation.

   On the exam: Beer Lambert calculations, calibration curve interpretation, and spectrophotometry data analysis appear as experimental context in Unit 3 free response questions.

2. 2

   What Makes a Good Solvent?

   Unit 3 · Properties of Substances and Mixtures

   Students systematically test the solubility of a variety of ionic, polar covalent, and nonpolar solutes in water, ethanol, and a nonpolar solvent, then explain each observation for intermolecular forces and the like dissolves like principle. The investigation requires students to move between three scales: the macroscopic observation of whether a solute dissolves, the symbolic representation of the solute and solvent structures, and the particulate level explanation of the force interactions that govern miscibility. Key concepts include hydrogen bonding, dipole dipole forces, London dispersion forces, and the energy balance between breaking solute and solvent interactions to form new solution interactions. Students evaluate why water dissolves ionic compounds by stabilizing ions but fails to dissolve nonpolar hydrocarbons, and why nonpolar solvents dissolve nonpolar solutes. The investigation grounds Unit 3 intermolecular force concepts in experimental evidence rather than assertion.

   On the exam: Intermolecular force reasoning and solubility explanation at the particulate level are among the most frequently assessed skills in Unit 3 free response questions.

3. 3

   What Is the Relationship between the Structure of a Solid and Its Properties?

   Unit 2 · Molecular and Ionic Compound Structure and Properties

   Students compare the melting point, hardness, solubility, and electrical conductivity of a set of solids representing the four types of crystalline structure: ionic, metallic, network covalent, and molecular. By measuring these bulk properties and linking each pattern to the forces holding the crystal together, students build a model of how atomic level bonding produces macroscopic material behavior. The investigation develops skill in constructing evidence based claims from multiple property observations rather than from a single measurement: a high melting point alone is insufficient to distinguish ionic from network covalent, but combining it with conductivity and solubility data narrows the identification. Students also practice writing Lewis diagrams and assigning formal charges for molecular solids as part of the analysis, reinforcing the Unit 2 structure and property framework throughout.

   On the exam: Relating solid structure to physical properties and justifying claims with multiple lines of evidence appear in Unit 2 and Unit 3 free response questions.

4. 4

   How Much Salt Is in My Soup? A Titration Investigation

   Unit 4 · Chemical Reactions

   Students determine the chloride concentration of a soup or saltwater sample by performing a potentiometric or indicator based precipitation titration using silver nitrate as the titrant and a standard curve or endpoint method for detection. The investigation introduces stoichiometric titration calculations in a context that bridges the classroom and everyday chemistry: students apply the mole ratio between silver ion and chloride, compute molarity from titration data, and compare their result to a known or accepted value to evaluate accuracy. Core skills developed include preparing and standardizing a titrant solution, identifying an appropriate indicator or detection method, performing multiple trials to assess precision, and propagating uncertainty through a stoichiometric calculation. Students also consider potential sources of systematic error in the titration procedure and discuss how each would affect the final result in a specific directional sense rather than generically.

   On the exam: Stoichiometric titration calculations, endpoint identification, and error analysis are core Unit 4 free response skills and appear on virtually every exam.

5. 5

   Sticky Question: How Do We Determine the Formula of a Hydrate?

   Unit 4 · Chemical Reactions

   Students heat a precisely weighed hydrated copper sulfate or calcium chloride sample, measure the mass lost on dehydration, and use the gravimetric data to determine the empirical formula of the hydrate by calculating the mole ratio of water to anhydrous salt. This investigation builds mastery of the mole concept in a clean and concrete setting: the measurement is mass, the goal is a mole ratio, and the procedure requires careful temperature control to ensure complete dehydration without decomposition of the anhydrous salt. Key skills include precise weighing technique, calculating moles from mass using molar mass, expressing the result as a ratio and converting to the nearest small integer, and evaluating whether a discrepancy from the theoretical formula reflects experimental error or a systematic problem such as incomplete dehydration or loss of the anhydrous compound at high temperature.

   On the exam: Gravimetric analysis, mole ratio calculations from mass data, and evaluation of experimental error sources are recurring stoichiometry and measurement skills on the exam.

6. 6

   What Is the Effect of Temperature on the Rate of a Reaction?

   Unit 5 · Kinetics

   Students measure the time required for a color change or other observable endpoint in a reaction, typically the iodine clock or a bleaching reaction, at several different temperatures and use the data to explore the Arrhenius relationship between temperature and rate constant. By plotting the natural logarithm of the rate constant against the reciprocal of absolute temperature, students determine the activation energy graphically and confirm that a modest temperature increase produces a substantial rate acceleration. The investigation develops skill in controlling temperature precisely with water baths, computing average rate from an observable endpoint time, applying the linearized Arrhenius equation, and interpreting the slope of an Arrhenius plot in physical terms as a function of activation energy. Students connect the macroscopic temperature effect to the particulate level explanation provided by the Maxwell Boltzmann speed distribution and the collision model.

   On the exam: Temperature dependence of reaction rate, the Arrhenius relationship, and graphical determination of activation energy appear in Unit 5 kinetics free response questions.

7. 7

   How Do the Structure of Acids and Bases Affect Their Behavior in Aqueous Solution?

   Unit 8 · Acids and Bases

   Students measure the pH of a series of acidic and basic solutions using a calibrated pH meter, comparing strong acids, weak acids, strong bases, weak bases, and salts of each category at the same nominal concentration. The core observation is that same concentration does not mean same pH when comparing strong and weak acids, and students must explain the difference quantitatively using the equilibrium constant Ka, the percent dissociation, and the particulate level picture of partial ionization. This investigation directly confronts the most persistent AP Chemistry misconception: that acidity scales linearly with concentration rather than with the equilibrium between the molecular and ionic forms of the acid. Students also compare pH predictions from Ka expressions against measured values, compute percent error, and identify sources of deviation such as activity effects at higher concentration or imprecise Ka literature values.

   On the exam: Acid and base strength, pH calculation from Ka and Kb, and relating molecular structure to acidic behavior are central Unit 8 free response skills.

8. 8

   How Does the Presence of a Buffer Affect pH?

   Unit 8 · Acids and Bases

   Students prepare an acetic acid and sodium acetate buffer at a target pH, add measured increments of strong acid or strong base, and compare the resulting pH change against the pH change in an unbuffered water sample receiving the same additions. The contrast makes buffer action concrete and quantitative: the buffer resists large pH swings because the conjugate acid base pair consumes added acid or base through its equilibrium, and the Henderson Hasselbalch equation predicts the approximate new pH after each addition. Key skills include choosing a buffer system with an appropriate pKa for the target pH, preparing solutions by mass and volume measurements, using a pH meter throughout the titration, and interpreting the flat buffer region and the inflection point on the resulting pH versus volume curve. Students compute buffer capacity from the data and compare it to the theoretical prediction from Henderson Hasselbalch.

   On the exam: Buffer preparation, pH prediction using Henderson Hasselbalch, and buffer capacity are among the highest yield and highest error topics on AP Chemistry free response questions.

9. 9

   How Effective Is an Antacid?

   Unit 8 · Acids and Bases

   Students perform a back titration to determine the neutralization capacity of a commercial antacid tablet, dissolving a known excess of hydrochloric acid with the antacid and then titrating the remaining acid with standardized sodium hydroxide to find how much acid was actually consumed. This investigation develops a layered stoichiometric reasoning skill that the AP Chemistry exam tests frequently: a back titration requires tracking two separate titrations, applying two separate mole relationships, and combining them to reach a conclusion about an analyte that could not be titrated directly. Core skills include standardizing a sodium hydroxide solution, performing two endpoint titrations, applying stoichiometry across both reactions, computing the acid neutralization equivalent per gram of antacid, and comparing results across tablet brands to evaluate which provides more neutralization per unit mass or cost.

   On the exam: Back titration calculations, stoichiometry across multiple reactions, and acid base neutralization appear in Unit 4 and Unit 8 free response questions.

10. 10

    Is It Hot in Here? The Chemistry of Hand Warmers

    Unit 6 · Thermochemistry

    Students dissolve several ionic compounds in water inside a calorimeter and measure the temperature change to determine the enthalpy of solution, comparing exothermic and endothermic candidates for use in a hand warmer or cold pack. The investigation builds the core calorimetry skill set: computing heat from q equals mc delta T, dividing by moles to get the molar enthalpy, accounting for heat capacity of the calorimeter itself, and assessing which assumptions in a simple coffee cup calorimeter introduce the most error. Students also evaluate practical criteria beyond just the magnitude of enthalpy change, including cost per use, safety, reversibility, and maximum operating temperature. The investigation emphasizes the distinction between the sign of the enthalpy change and the practical direction of the temperature effect, which is a perennial student error documented in AP Chemistry Chief Reader Reports.

    On the exam: Calorimetry calculations including q equals mc delta T, molar enthalpy determination, and error analysis are among the most frequently tested Unit 6 free response skills.

11. 11

    Where Does the Energy Come From in Chemical Reactions?

    Unit 6 · Thermochemistry

    Students use Hess's law experimentally by measuring the enthalpy changes of two or three related reactions via constant pressure calorimetry and then combining the measured values algebraically to predict the enthalpy of a fourth reaction that cannot be measured directly. The investigation makes Hess's law an empirical fact rather than an abstract rule: students see that enthalpy is a state function because the measured target enthalpy matches the Hess combination to within reasonable experimental error. Core skills include setting up and running calorimetric experiments with careful temperature tracking, applying the sign convention for reversing and scaling reactions, computing uncertainty from the variance across trials, and evaluating whether the discrepancy between the predicted and measured total enthalpy falls within the expected experimental uncertainty or suggests a systematic error. Students also practice representing enthalpy cycles with diagrams that show intermediate steps.

    On the exam: Hess's law applications, enthalpy cycle construction, and calorimetric data interpretation are recurring Unit 6 free response topics.

12. 12

    How Can We Determine the Rate Law for a Chemical Reaction?

    Unit 5 · Kinetics

    Students measure the initial rate of a reaction, typically the iodine clock or crystal violet bleaching, at multiple initial concentrations of each reactant and apply the method of initial rates to determine the order regarding each reactant and the overall rate law. This investigation is the primary vehicle for building the kinetics quantitative skill set that the AP Chemistry exam tests most heavily in Unit 5: isolating one variable at a time, computing a ratio of initial rates to extract an exponent, combining orders to write the overall rate law, and calculating the rate constant from experimental data. Students compare their experimentally determined orders to the stoichiometric coefficients of the balanced equation and recognize that the rate law cannot be inferred from the equation alone, which directly addresses a documented AP Chemistry student misconception. Error analysis focuses on identifying which steps in the procedure most strongly affect the accuracy of the determined rate constant.

    On the exam: Determining rate law by the method of initial rates and interpreting concentration versus time data are core Unit 5 free response skills and appear on virtually every exam.

13. 13

    What Is the Relationship between pH and the Ratio of Acid to Conjugate Base in a Buffer Solution?

    Unit 7 · Equilibrium

    Students prepare a series of buffer solutions with varying ratios of a weak acid to its conjugate base, measure the pH of each, and compare the measured values against the Henderson Hasselbalch prediction to build an experimental picture of how the equilibrium constant governs the pH of a buffer. The investigation extends the equilibrium unit by treating buffers as a concrete test case for the relationship between Q, K, and equilibrium concentration. Students plot pH against the log of the conjugate base to acid ratio and determine the pKa graphically from the x intercept of that relationship, then compare the graphically determined pKa to the literature value. Core skills include serial preparation of buffer solutions, careful pH measurement across a range, constructing a graphical treatment of equilibrium data, and interpreting how the ratio controls pH rather than the absolute concentrations of the components.

    On the exam: Equilibrium constant reasoning, Henderson Hasselbalch quantitative applications, and buffer composition questions appear across Unit 7 and Unit 8 free response questions.

14. 14

    How Can We Control the Conditions of a Chemical Reaction?

    Unit 7 · Equilibrium

    Students investigate Le Chatelier's principle by observing how a visible equilibrium system, typically the cobalt chloride or iron thiocyanate system, shifts in response to changes in concentration of a reactant or product, changes in temperature, and in some versions changes in pressure or volume. The investigation requires students to predict the direction of each shift before observing it, then explain the observation at the particulate level by analyzing how the perturbation moves the reaction quotient Q away from the equilibrium constant K and how the system responds to restore equilibrium. Key skills include writing the equilibrium expression for a reaction, computing Q at each perturbation, predicting shift direction from comparing Q to K, and distinguishing between changes that alter K itself versus changes that only shift concentrations without changing the equilibrium constant. The temperature perturbation is particularly important because it forces students to identify whether the reaction is exothermic or endothermic before predicting the shift.

    On the exam: Le Chatelier applications including Q versus K analysis, shift direction prediction, and the effect of temperature on K appear in every Unit 7 free response cluster.

15. 15

    How Can We Verify the Principle of Conservation of Energy Using Electrochemical Cells?

    Unit 9 · Thermodynamics and Electrochemistry

    Students construct galvanic cells using combinations of metal electrodes and their corresponding aqueous ion solutions, measure the cell potential with a voltmeter, and compare the measured potential against the standard cell potential predicted from the standard reduction potential table. The investigation builds the electrochemistry skill set that became a higher priority after the 2024 AP Chemistry CED revision folded electrochemistry fully into Unit 9: identifying the anode and cathode, writing the half reactions and overall cell reaction, computing the standard cell potential from standard reduction potentials, and recognizing the sign conventions that distinguish galvanic from electrolytic operation. Students also vary the concentration of one ion to observe a qualitative Nernst effect, comparing whether the measured cell potential shifts in the direction predicted by the relationship between concentration and equilibrium. Error analysis addresses the junction potential and electrode surface effects that cause real cell potentials to deviate from standard predictions.

    On the exam: Galvanic cell potential, half reaction writing, standard reduction potential calculations, and qualitative Nernst reasoning appear in Unit 9 free response questions.

16. 16

    How Much Electricity Does It Take to Plate a Metal?

    Unit 9 · Thermodynamics and Electrochemistry

    Students pass a measured electrical current through an electrolytic cell for a controlled time, plate a known metal such as copper onto a weighed cathode, and use Faraday's law to predict the mass deposited based on the charge passed, then compare the prediction to the actual mass gained. This investigation makes Faraday stoichiometry concrete: the charge in coulombs equals current in amperes times time in seconds, and the conversion from charge to moles of electrons to moles of metal to grams follows from the half reaction and the molar mass. Core skills include setting up and operating an electrolytic cell safely, using an ammeter to monitor current and adjusting to maintain constant current, tracking time precisely, weighing the cathode before and after plating, and computing current efficiency as the ratio of actual mass to theoretical mass. Deviation from 100% efficiency is analyzed for side reactions, hydrogen evolution, and current variation during the experiment.

    On the exam: Faraday stoichiometry, electrolysis calculations connecting charge to moles of metal, and electrolytic cell operation appear in Unit 9 free response questions.

These 16 guided inquiry investigations form College Board's recommended AP Chemistry lab program (AP Chemistry Guided Inquiry Experiments: Applying the Science Practices). College Board expects teachers to implement a minimum number of hands on investigations to meet the curricular requirement of roughly 25% instructional time as lab work, covering all 9 units. Virtual simulations may supplement but are not intended to replace hands on quantitative work for the investigations that require direct measurement and error analysis.