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Edward Avetisyan Richard Engeseth Tuesday 11am-1:50pm 2/20/2023 Chem 102 Lab 5 Objective ● Appyling the concepts of dynamic equilibrium through Le Chatliers principle by observing the effects of disturbing an equilibrium by changing temperature and concentration. Procedures ● Chromate and Dichromate Equilibrium ○ 1) In a clean test tube, place 1-2 mL of 1 M K 2 CrO 4 . Add a few drops of 3 M H 2 SO 4 . Shake the tube and write down the observations made. ○ 2) Add one drop of 6 M NaOH and mix. Continue to add single drops until you observe a color change. ○ 3) Add a few drops of 3 M H 2 SO 4 until you observe a color change. ○ 4) Add one drop of 6 M NaOH and mix. Continue adding single drops until you observe a color change. ● Indicator Equilibrium ○ 1) Place 2-3 mL of deionized water in a test tube and add 2-4 drops of 1% methyl orange. Now add 2 drops of 6 M HCl. Observe and record the color change. Add 4 drops of 6 M NaOH. Observe and record the color change. ○ 2) To one tube, add 1 M sodium acetate a few drops at a time. Mix the solution until you see a change. Compare the color of this tube with the original one and record your observations. ○ 3) Add a few drops of 1 M NH 4 OH, weak base, to each of the solutions. Observe any changes and record your observations. ● Temperature ○ 1) Place 4 mL of .15 M CoCl 2 *6H 2 O dissolved in methanol into a test tube drop- by-drop until the blue solution turns pink. Pour half of the pink solution turns pink. ○ 2) Pour half of the pink solution into a second test tube. ○ 3) To one of the test tubes add 12 M HCl dropwise until you see a color change. ○ 4) Heat the second test tube (no acid) in a water bath filled with hot water. If there is no color change, raise the temperature of the water bath. ○ 5) Using the solution you heated in step 4, place the test tube in an ice bath. ● Concentration and temperature ○ 1) Place around 4 mL of saturated KCl solution into a test tube. Carefully add 2 mL of concentrated 12 M HCl. Mix the solution.

○ 2) Warm the solution using a beaker of hot water on a hot plate. Note the presence of absence of precipitate and the amount of precipitate. Observations/ Results Chromate and dichromate equilibrium CrO 4 2- (aq) + 2 H + (aq) Cr ⇌ 2 O 7 2- (aq) + H 2 O(l) 1. (½ point) What substance, chromate or dichromate, is most abundant if the solution is yellow? Chromate 2. (½ point) What substance, chromate or dichromate, is most abundant if the solution is orange? DiChromate 3. (1 point) Addition of H + (aq) to the above equilibrium produces an Orange (insert color) solution and pushes the equilibrium to the Right (left/right) 4. (1 point) Addition of OH - (aq) to the above equilibrium produces an Yellow (insert color) solution and pushes the equilibrium to the Left (left/right) Indicator Equilibria The equilibria are generalized as: HIn(aq) H ⇌ + (aq) + In - (aq) 1. (½ point) What color is HIn for methyl orange? HIn for methyl orange 2. (½ point) What color is In - for methyl orange? In - 3. (½ point) Which way does the methyl orange equilibrium above shift upon addition of HCl? Upon addition of HCl equilibrium shifts left

4. (½ point) Which way does the methyl orange equilibrium above shift upon addition of NaOH? Upon addition of NaOH equilibrium shifts right 5. (½ point) What color is HIn for phenolphthalein? HIn of phenolphthalein is colorless 6. (½ point) What color is In - for phenolphthalein? In - for phenothalien is pink 7. (½ point) Which way does the phenolphthalein equilibrium above shift upon addition of HCl? Upon addition of HCl equilibrium shifts to the left 8. (½ point) Which way does the phenolphthalein equilibrium above shift upon addition of NaOH? Upon addition of NaOH the phenophthalien equilibrium shifts to the right Weak Acid Equilibria HCH 3 CO 2 (aq) CH ⇌ 3 CO 2 - (aq) + H + (aq) 1. (½ point) What color is the acetic acid plus methyl orange solution and what does this tell you about where the equilibrium is? The color of the solution is orange and the indicator equilibrium will shift towards the right 2. (½ point) What color is the acetic acid plus methyl orange after addition of sodium acetate solution and what does this tell you about where the equilibrium is? The color of the solution is yellow due to the formation of acetate ion from sodium acetate the dissociation of acetic acid reduces and pH increases. The indicator equilibrium will shift towards the left.

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3. (½ point) What color is the acetic acid plus methyl orange plus sodium acetate solution after addition of ammonium hydroxide and what does this tell you about where the equilibrium is? The adittion of ammonium hydroxide makes the solution baesic anf the solution will turn yellow. The indicator equilibrium will shift to the left. Ion Equilibria Fe 3+ (aq) + SCN - (aq) Fe(SCN) ⇌ 2+ (aq) 1. (½ point) What color is tube 1 and what does this tell you about the position of the above equilibrium? Red-orange color indicates that the equilibrium is beginning to shift towards Ferric Tiocyanate complex Fe(SCN) 2+ ions due to high concentration of SCN - ions. 2. (½ point) What color is tube 2 and what does this tell you about the position of the above equilibrium? Deep red color indicates that the equilibrium is strongly in favor of Fe(SCN) 2+ ions due to high concentration of SCN - ions. Shift right. 3. (½ point) What color is tube 3 and what does this tell you about the position of the above equilibrium? Wine red or bloodish red color indicates that the equilibrium is strongky in favor of Fe(SCN) 2+ ions due to the addition of Fe 3+ ions. Shift right. 4. (½ point) What color is tube 4 and what does this tell you about the position of the above equilibrium? The golden yellow color indicates that the equilibrium had shifted towards the reactants due to the removal of Fe 3+ ions from solution. The precipitate indicates the formation indicates the formation of insoluble salt due to the Fe 3+ ions from solution. The precipitate indicates the formation of insoluble salt due to the Fe 3+ ions removed.

5. (1 point) Briefly explain how the reaction in tube 4 supports Le Châtelier’s principle. Le Chatelier principle state that whenever a system in equilibrium is disturbed the system will adjust itself in such a way that the effect of the change will reduce or moderate. In test tube 4, the system is distutbubed by reducing Fe 3+ ions in the system. Thus, it will adjust itself to reduce the change or it will tent to increase Fe 3+ ion concentration to compenstate for loss. Therefore, Ferric Thiosulfate (Fe(SCN) 2+ ) ion will decompose giving back Fe 3+ and SCN - ions and the equilibrium will shift towards the reactants. s Temperature Dependence of Ion Equilibria 1. (½ point) What color is your solution in hot water? The solution is blue in hot water 2. (½ point) What color is your solution in ice water? The solution is pink in ice water 3. (1 point) Using the color changes you observed, is the reaction CoCl 2 (H 2 O) 2 (aq) + 4 H 2 O(l) Co(H ⇌ 2 O) 6 2+ (aq) + 2 Cl - (aq) exothermic or endothermic? Briefly explain how you deduced this. The solution is exothermic because adding heat causes the equilibrium shift to the left. While decreasing heat causes the equilibrium to shift right. Concentration and Temperature Effects on Solubility KCl(s) K ⇌ + (aq) + Cl - (aq) 1. (½ point) Which way does the above equilibrium shift upon addition of HCl? Upon addition of Hcl the equilibrium will shift to the left. 2. (½ point) Is KCl more or less soluble in hot water versus cold water? KCl is more soluble in hot water 3. (½ point) Is the equilibrium above exothermic or endothermic? Briefly explain using shifts in equilibrium to explain your conclusions.

The equilibrium is endothermic in nature because the coolin will be their on addition of KCl in water. Conclusion ● We observed that the effect ofg concentration, pH, and temperature in accordance with Le Chetalier’s Principle ● For Chromate and dichromate equilibrium, an orange solution indicates the eq has been shifted to the right and a yellow solution indicates that the eq has been shifted to the left. ● For indicator equilibrium, a pink solution indicates a basic solution ● For weak acid equilibrium, a red-orange color indicates a left shift and a yellow indicates a right shift. ● For an ion eq red indicates a shift in the right direction and a yellow indicates a shift in the left direction ● The Ionic equilibrium observed was exothermic ● KCl is more soluble in hot water, indicaiting that it is endothermic.

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