Be sure to show all work, round answers, ____________________, Did the value of \(K_{sp}\) get smaller or larger? Set up a hot-water bath by filling a 400-mL beaker about half-full with tap water and heating the water using a Bunsen burner while you work on the following steps. To … As the concentration of product C … Observe what happens and record your observations. Now let’s consider the process of precipitation. It is a control for comparison with other tubes. Continue heating and stirring until a change is observed. Equilibrium system: \(\ce{PbCl2 (s) <=> Pb^{2+} (aq) + 2 Cl^{–} (aq)}\) The hot-water bath will be used in Step 4. Explain your answer using Le Chatelier’s principle. In fact, a very small amount of each of these substances does dissolve in aqueous solution, but the amount is so small that we often classify each of these compounds as, “insoluble”. Eventually, all the precipitate settles to the bottom of your test tube. Note that for a heterogeneous system including pure solids or liquids of the form, \[a \text{A} (aq) + b\text{B} (s) \ce{<=>}c\text{C} (aq) + d\text{D} (l) \label{3}\]. • Answer the pre-lab questions that appear at the end of this lab exercise. In other words you will be able to determine whether the equilibrium position lies to the left (more reactants and less products) or whether the equilibrium lies to the right (more products and less reactants). The entire class will then use this stock solution in Part 5. Stir the contents of the test tube gently for a few seconds using the glass stirring-rod and record your observations on your data sheet. Decrease in all aqueous concentrations due to an increase in solution volume resulting from the addition of solvent, Shift towards side with more solute particles, Increase in all aqueous concentrations due to a decrease in solution volume resulting from the removal of solvent (evaporation), Shift towards side with less solute particles, Increase temperature of an exothermic reaction, Decrease temperature of an exothermic reaction, Increase temperature of an endothermic reaction, Decrease temperature of an endothermic reaction, Addition of an inert substance, catalyst, pure liquid, or pure solid. The purpose of this lab is to observe the effects of a stress placed on an equilibrium system. Answer: (b) 5. In Part D you will use coupled equilibria to affect the solubility equilibrium of \(\ce{Zn(OH)2 (s)}\). Reagents needed are: 0.3 M \(\ce{Pb(NO3)2}\) (aq), 0.3 M \(\ce{HCl}\) (aq), and deionized water. Instead of directly adding \(\ce{HA}\) or \(\ce{A^{-}}\) to the system, you will effect these shifts by adding \(\ce{H^{+}}\) or \(\ce{OH^{-}}\). The solubility equilibrium can be described by the equation, \[\ce{Zn(OH)2 (s) <=> Zn^{2+} (aq) + 2OH^{-} (aq)}\quad\quad K_{sp} = 5 \times 10^{-17} M^{3} \label{16}\]. It is not necessary to dry glassware since all reagent volumes are approximate and all solutions are aqueous. The major steps involved in the process are: The crucial step is the oxidation of sulfur dioxide, SO2 to sulfur trioxide, SO3. Your solution from Step 1 currently contains one form of bromothymol blue (see background). We can perturb the equilibrium position of Reaction \ref{6} by the addition of some \(\text{C} (aq)\).The addition of \(\text{C} (aq)\) will cause the equilibrium position of Reaction \ref{6} to shift right in accordance with Le Chatelier’s Principle. Dispose of all chemical waste in the plastic container in the hood. One noticed how a strong acid and strong base effects buffered and unbuffered systems. Into test tube D, add at least 20 drops of 6 M \(\ce{HCl}\) (, Into test tube E, add at least 20 drops of 6 M \(\ce{NaOH}\) (, Into test tube F, add at least 20 drops of 6 M \(\ce{NH3}\) (. To the solution in test tube #3, first add a medium scoop of solid \(\ce{NH4Cl}\). In which direction (left or right) would the following stresses cause the system to shift? Common ligands include \(\ce{H2O}\), \(\ce{NH3}\), \(\ce{Cl^{–}}\), and \(\ce{OH^{–}}\). Decreasing the concentration of \(A\) or \(B\) causes a shift to the left. Version 42-0166-00-02 Review the safety materials and wear goggles when working with chemicals. Here you will test the effects of changing the volume and temperature on the complex ion equilibrium between Co(H2O)62+ (aq) and CoCl42- (aq) as in Reaction \ref{14}. Label the beaker and place it on the front desk. Firmly hold test tube #3 with your test tube holder, and waft it back and forth through the flame (to prevent overheating and “bumping”) for about 30 seconds, or, until a distinct change occurs. Notice that \(K_{sp} << 1\) for this reaction, demonstrating that \(\ce{Zn(OH)2 (s)}\) is only very slightly soluble in aqueous solution. In exothermic reactions, heat energy is released and can thus be considered a product. The questions should be answered on a separate (new) page of your lab notebook. Answer: (c) 4. One … Calculate \([\ce{Pb^{2+}}]\) and \([\ce{Cl^{–}}]\) in the final solution (consider the “dilution effect”). Stir each solution and record your observations. Explain why reagent A (in Step 2) caused the color change observed. When temperature or concentration are changed, the stress is placed on either of the reactant or products side. Make a cold-water bath by filling a 400-mL beaker half full with tap water and ice. Examples of stresses include increasing or decreasing chemical concentrations, or temperature changes. These are supplied in the Theory Section. Experiment Summary: In this experiment, you will describe the components … Question: Le Chatelier's Principle Lab Report, Pages 6-7 Data Table 1: Part I. Notice that the species \(\text{B} (aq)\) is common to both reactions. The concentrations of reactants and products at equilibrium are constant as a function of time. This is because of the structure and polar nature of the CO molecule, which causes it to bind strongly with the Hb^+1. Observations upon addition of \(\ce{HCl}\): In which direction did this stress cause the equilibrium system to shift? Add the 6 M reagent of your choice. Cool the test tube down by placing it into this cold-water bath. Chemical equilibrium is a dynamic state. To observe the effect of an applied stress on chemical systems at equilibrium. Thus, we can use the values of \(Q_{sp}\) and \(K_{sp}\) to predict the conditions under which a precipitation reaction will occur. A reversible reaction at equilibrium can be disturbed if a stress is applied to it. Le Chatelier’s Principle Experiment 5 Le Châtelier’s Principle Pre-Lab Assignment Before coming to lab: • Read the lab thoroughly. In Part B we will study the solubility equilibrium of \(\ce{PbCl2 (s)}\). Consider the following exothermic reversible reaction at equilibrium: \[\ce{2A <=> B + C}\] [ "article:topic", "Le Chatelier\'s Principle", "authorname:smu", "showtoc:no", "license:ccbync" ], https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FAncillary_Materials%2FLaboratory_Experiments%2FWet_Lab_Experiments%2FGeneral_Chemistry_Labs%2FOnline_Chemistry_Lab_Manual%2FChem_12_Experiments%2F03%253A_Le_Chatelier's_Principle_(Experiment), 2: Determination of Kc for a Complex Ion Formation (Experiment), 4: Determining the Equivalent Mass of an Unknown Acid by Titration (Experiment), Lab Report: Properties of Systems in Equilibrium - Le Chatelier’s Principle, Part A – Equilibrium and an Acid-Base Indicator, Part B – Solubility Equilibrium and \(K_{sp}\), Pre-Laboratory Assignment: Le Chatelier’s Principle, information contact us at info@libretexts.org, status page at https://status.libretexts.org. When a reaction makes more reactants in response to the perturbation, we call it a left-shift. Carbon monoxide is a poison that prevents the hemoglobin molecule from binding with the oxygen in the lungs. Then heat this solution directly in your Bunsen burner flame (moderate temperature). Lab 3 Le Chateliers Principle Green River College. The bottle should be kept in a plastic tray and not removed from the fume hood. ____________________, Is the dissolution of \(\ce{PbCl2}\) (s) exothermic or endothermic? When callers reach a company free of an answering message program, the experience could in fact be seriously irritating. One studied the effects of concentration and temperature changes on an equilibrium system. ______________________, Did the value of K get smaller or larger? Legal. Label the beaker and place it on the front desk. Because Reactions \ref{17}, \ref{18}, and \ref{19} each share a common species with Reaction \ref{16} they can be coupled together. Add 1-mL of 0.1 M \(\ce{FeCl3}\) (aq) and 1-mL of 0.1 M \(\ce{KSCN}\) (aq) to a 150-mL (medium) beaker, top it up with 100-mL of distilled water, and mix with a stirring rod. In Part C you will study the following complex ion formation reaction: \[\ce{Co(H2O)6^{2+} (aq) + 4Cl^{-} (aq) <=> CoCl4^{2-} (aq) + 6H2O (l)} \label{14}\], The equilibrium-constant expression for Reaction \ref{14} is, \[K_{f}= \frac{[\ce{CoCl4^{2-}}]}{[\ce{Co(H2O)6^{2+}}][\ce{Cl^{-}}]^{4}} \label{15}\]. It is a reversible reaction. Chemfax Apllications Of Lechateliers Principle Prelab Answers. Because \(\text{B} (aq)\) is also present in Reaction \ref{5}, the decrease in the concentration of \(\text{B} (aq)\) will in turn result in a right shift in the equilibrium position of Reaction \ref{5}. The second reaction is the autoionization of water, which can be described by the equation, \[\ce{ H2O (l) <=> H^{+} (aq) + OH^{-} (aq)} \label{9}\], The equilibrium constant for this reaction is denoted by \(K_{w}\), where the subscript \(w\) stands for water, and the associated equilibrium constant expression is, \[K_{w}= [\ce{H^{+}}][\ce{OH^{-}}] \label{10}\]. This is related to le chatelier’s principle lab answer key. Thoroughly rinse the graduated cylinder with deionized water, then measure 5.0 mL of the 0.3 M \(\ce{HCl}\) solution using the 10-mL graduated cylinder. Lab Worksheet for "Chemical Equilibrium and Le Chatelier's Principle" General Instructions: • Complete Part A, Part B Steps 1a-1e (skip 1f) and Steps 2a-2e (skip 2f-2i). Read the entire exercise before you begin. Given that the above reaction is endothermic, should you heat the solution, or cool the solution in order to change the color from light blue to violet? Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise. Explain why you do not see the precipitate initially as you first begin to add \(\ce{NaOH}\) (aq). Chemical equilibrium has been reached in a reaction when the rate of the forward reaction is equal to the rate of the reverse reaction. Notice that only a temperature change can affect the value of \(K_{c}\); in all other cases the value of \(K_{c}\) remains constant. Record all observations on your report form. Equipment: 10 small test tubes, test tube rack, test tube holder, Bunsen burner, 2 medium-sized beakers (for stock solutions), 10-mL graduated cylinder, wash bottle, stirring rod, and scoopula. The solution in test tube #1 remains untouched. A reversible reaction is a reaction in which both the conversion of reactants to products (forward reaction) and the re-conversion of products to reactants (backward reaction) occur simultaneously: \[\text{Reactants} \ce{->} \text{Products}\], \[\text{Products} \ce{->} \text{Reactants}\]. You add a small amount of \(\ce{NaOH}\) to a test tube containing cadmium nitrate solution. Consider the case of a reversible reaction in which a concentrated mixture of only \(A\) and \(B\) is supplied. Note that when a reaction makes more products as a response to the perturbation, we call it a right-shift. The hot-water bath will be used in Step 6 (and also in Part C). Expt 9-Chemical Equilibrium. Observations, In which direction did the equilibrium shift? Explain why you eventually do see a precipitate. the pure liquids and solids do not appear in the equilibrium-constant expression: \[K_{c}= \frac{[\text{C}]^{c}}{[\text{A}]^{a}} \label{4}\]. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. ______________________, Is the reaction (as written) exothermic or endothermic? To the solution in test tube #2, add 1-mL of 0.1 M \(\ce{FeCl3}\) (, To the solution in test tube #3, add 1-mL of 0.1 M \(\ce{KSCN}\) (, To the solution in test tube #4, add 0.1 M \(\ce{AgNO3}\) (, What happens to the forward and reverse reaction, What happens to the reactant (\(A\) and \(B\)) and product (\(C\) and \(D\)). At normal conditions, the equilibrium lies far to the left and the amount o… Add about 1 mL of the 0.3 M \(\ce{HCl}\) solution to the \(\ce{Pb(NO3)2}\) solution in the large test tube. The amounts of reagents used in this experiment are approximate only. Using similar logic, the following changes in concentration are expected to cause the following shifts: In other words, if a chemical is added to a reversible reaction at equilibrium, a shift away from the added chemical occurs. Follow the procedure in the lab manual and record your data on this worksheet. Adopted a LibreTexts for your class? The color of \(\ce{Cu(CN)4^{2-}}\) (aq) is light blue, while the color of \(\ce{Cu(NH3)4^{2+}}\) is violet. Questions are typically answered in as fast as 30 minutes. where we denote the equilibrium constant, \(K\), with a subscript \(a\) for acid. where we denote the equilibrium constant, \(K\), with a subscript \(f\) for complex ion formation. By observing the changes that occur (color changes, precipitate formation, etc.) In Part D of this experiment you will observe the effect of coupling each of these equilibria on the solubility of \(\ce{Zn(OH)2 (s)}\). If a system in dynamic equilibrium is subjected to a stress such as changes in concentration, temperature, volume, and partial pressures, the concentration of products and reactants change to reestablish the equilibrium constant, Kc. Note that, upon mixing two solutions, one containing \(\text{A}^{+}\) and the other containing \(\text{B}^{-}\), if \(Q_{sp} H2O (l)}\]. If the solution is overheated it will splatter out of the tube, so be careful not to point the tube towards anyone while heating. Explain the observed color change that occurred when water was added to the solution in Step 3. Le Chatelier's principle states that changes in pressure are attributable to changes in volume. Adopted a LibreTexts for your class? Le Châtelier’s Principle Pre-lab Assignment Before coming to lab: • Read the lab thoroughly. where \(Q_{sp}\) is called the solubility product reaction quotient. we can express the equilibrium-constant expression for this reaction as, \[K_{c}= \frac{[\text{C}]^{c}[\text{D}]^{d}}{[\text{A}]^{a}[\text{B}]^{b}} \label{2}\], where the values of \([\text{A}]\), \([\text{B}]\), \([\text{C}]\), and \([\text{D}]\) correspond to the equilibrium concentrations (or equilibrium positions) of all the aqueous chemical components, and \(a\), \(b\), \(c\), and \(d\) are their respective stoichiometric coefficients. Such shifts may then be explained by carefully examining the effect of the applied stress as dictated by Le Chatelier’s Principle. Since the two forms are different colors, you will be able to determine which form is predominant in the equilibrium mixture. For part A, since it was increased on the reactant side, the equilibrium will shift toward the product side. It can be explained as follows. What color change might you expect to observe? Add a medium scoop of \(\ce{NH4Cl}\) powder to the solution in this test tube. All chemical reactions eventually reach a state in which the rate of the reaction in the forward direction is equal to the rate of the reaction in the reverse direction. Cadmium hydroxide, an important component of \(\ce{NiCd}\) batteries, is only slightly soluble in water. To perturb chemical reactions at equilibrium and observe how they respond. Explain your answer using Le Chatelier’s principle. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Certain metal ions, most often transition metals, exist in solution as complex ions in combination with other ions or molecules, called ligands. Answer. Le Chatelier s Principle Lab AP Chemistry Krebs 2012 2013. Because Reactions \ref{7} and \ref{9} share a common chemical species (\(\ce{H^{+}}\)), you can use the concept of coupled equilibria to shift the equilibrium position of Reaction \ref{7} by increasing or decreasing the concentration of \(\ce{OH^{-} (aq)}\). Which of the following reagents, 6 M \(\ce{HCl}\) or 6 M \(\ce{NaOH}\), will cause the solution to change color? You will then observe how each reaction responds to that perturbation in order to restore equilibrium. Box 219 Batavia, IL 60510: Phone: 800-452-1261: Fax: 866-452-1436: Email: flinn@flinnsci.com This right shift in the equilibrium position of Reaction \ref{6} will also result a corresponding decrease in the concentration of \(\text{B} (aq)\). What form of the complex ion, \(\ce{Co(H2O)6^{2+}}\) (, Explain why you obtained the observed color in 12 M \(\ce{HCl}\) (. In a typical precipitation reaction two aqueous salt solutions are mixed together resulting in the production of an insoluble salt. Reagents needed for this part are: \(\ce{CoCl2*6H2O}\) (s), 12 M \(\ce{HCl}\) (aq) (do not remove from fume hood), and deionized water. Consider your observations in the hot water bath in Step 4. All of the acids and bases used in this experiment (\(\ce{NH3}\), \(\ce{HCl}\), \(\ce{HNO3}\) and \(\ce{NaOH}\)) can cause chemical burns. Eventually the forward reaction would slow down and the forward and backward reaction rates become equal again as the system returns to a state of equilibrium. Explain why reagent B (in Step 3) caused the color change observed. Be sure to show all work, round answers, and include units on all answers. Name: ____________________________ Lab Partner: ________________________, Date: ________________________ Lab Section: __________________, Equilibrium system: \(\ce{ HA (aq) <=> H^{+} (aq) + A^{-} (aq)}\). • Answer the pre-lab questions that appear at the end of this lab exercise. The animation is showing in the yellow panels that the molecules are colliding and reforming and then repeating this process numerous times. Note that in order to determine the effect of \(\ce{OH^{-}}\) we must consider a second chemical reaction that shares a common species with the Reaction \ref{7}. Save this cold-water bath for use in Part C. Dispose of the remainder of the 0.3 M \(\ce{HCl}\) solution in your 10-mL graduated cylinder by pouring it into the appropriate waste container and then rinse the cylinder using deionized water.
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