La Châtelier s Principle Science Olympiad Edgewood Regional

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Laurence Fletcher
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1 La Châtelier s Principle School: I will demonstrate several reactions for you and ask questions regarding the reagents and results. REACTION 1 Tetrachlorocobaltate(II) [left] and hexaaquacobalt(ii) equilibrium [right] 1. Write the equilibrium equation here: (Hint: one complex has a 2+ charge and the other 2- ) Tetrachlorocobaltate(II) is red and hexaaquacobalt(ii) is blue. I will add the first reagent to the tetrachlorocobaltate(ii) in the test tube. 2. What color did the solution turn? 3. Did the equilibrium shift to the right or to the left? 4. Which of these reagents was added? a. H 2 0 b. Cobalt (II) chloride c. HCl d. HCO 3 I will add the second reagent. 5. What color did the solution turn? 6. Did the equilibrium shift to the right or to the left?

2 7. Which of these reagents was added? a. HCl b. H 2 O c. MeOH d. Potassium Bromate REACTION 2 Fe 3+ + SCN - and FeSCN 2+ ion equilibrium (FeSCN 2+ is a deep red) 11. Write the chemical equation here: I will add the first reagent to the Fe(NO 3 ) 3 in the test tube. 12. What ion was added to the test tube? 13. What color did the solution turn? 14. What compound was formed? 15. Did the equilibrium shift to the right or to the left? I will add the second reagent to the test tube. 16. What color did the solution turn? Any other observations? 17. Did the equilibrium shift to the right or to the left? 18. Which of these reagents was added? a. Fairy Dust b. H 2 O c. HCl d. AgNO 3

3 School: Dissolution of NH 4 Cl Equilibrium There is a test tube on your table or hood containing a saturated solution of ammonium chloride. One of your team members will hold the test tube (WITH GLOVES ON) after I add a few drops of concentrated HCl. Note your observations here: Next, another team member will hold a test tube containing ammonium chloride crystals. I will add water to the test tube. Note your observations here: Write the chemical equation for the dissolution of ammonium chloride: Is the dissolution of ammonium chloride exothermic or endothermic?

4 School: Chemistry Quick Quiz Answer the following questions to the best of your ability. You might not finish before the time limit. Good luck! For the reaction shown, calculate how many moles of NO 2 form when 10.5g of N 2 O 2 completely reacts. Number of moles of NO 2 : 2 N 2 O 2 (g) 4 NO 2 (g) + O 2 (g) 4. Lead ions can be precipitated from solution with KCl according to the reaction below. When 28.5g KCl is added to a solution containing 25.7g Pb 2+, a PbCl 2 precipitate forms. The precipitate is filtered and dried and found to have a mass of 29.4g. Determine the limiting reactant, theoretical yield of PbCl 2, and percent yield for the reaction. Pb 2+ (aq) + 2 KCl(aq) PbCl 2 (s) + 2 K + (aq) Limiting reactant: Theoretical yield PbCl 2 : Percent yield PbCl 2 : 5. A cylinder contains 28.5L of oxygen gas at a pressure of 1.8 atm and a temperature of 298K. How much gas (in moles) is in the cylinder? Number of moles of gas:

5 6. Consider the chemical reaction below. How many liters of hydrogen gas are formed from the complete reaction of 15.7g C? Assume that the hydrogen gas is collected at a pressure of 1.0 atm and a temperature of 355K. Liters of hydrogen gas: C(s) + H 2 O(g) CO(g) + H 2 (g) 7. Classify the following reactions (i.e. acid/base, redox); one of these could be classified as two types: K 2 CO 3 (aq) + NiCl 2 (aq) NiCO 3 (s) + 2 KCl(aq) H 2 SO 4 (aq) + 2KOH(aq) 2 H 2 O(l) + K 2 SO 4 (aq) 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g), 8. Predict the products of the following reactions and balance them. If no reaction occurs, write no reaction : LiI(aq) + BaS(aq) KCl(aq) + CaS(aq) CrBr 2 (aq) + Na 2 CO 3 (aq) NaOH(aq) + FeCl 3 (aq)

6 La Châtelier s Principle School: I will demonstrate several reactions for you and ask questions regarding the reagents and results. This worksheet is based off of a lab I did in general chemistry at Edgewood College REACTION 1 Tetrachlorocobaltate(II) [left] and hexaaquacobalt(ii) equilibrium [right] *Note: it is not required for students to know how to name complexes for the state competition. I included this because students who understand naming could potentially make the critical thinking leap to derive the compounds from the names. 1. Write the equilibrium equation here: (Hint: one complex has a 2+ charge and the other 2- ) [CoCl 4 ] H 2 O [Co(H 2 O) 6 ] Cl - Tetrachlorocobaltate(II) is red and hexaaquacobalt(ii) is blue. I will add the first reagent to the tetrachlorocobaltate(ii) in the test tube. 2. What color did the solution turn? blue 3. Did the equilibrium shift to the right or to the left? right 4. Which of these reagents was added? a. H 2 0 b. Cobalt (II) chloride c. HCl d. HCO 3 I will add the second reagent. 5. What color did the solution turn? Red or pink 6. Did the equilibrium shift to the right or to the left? left

7 7. Which of these reagents was added? a. HCl b. H 2 O c. MeOH d. Potassium Bromate REACTION 2 Fe 3+ + SCN - and FeSCN 2+ ion equilibrium (FeSCN 2+ is a deep red) 11. Write the chemical equation here: Fe 3+ + SCN - FeSCN 2+ I will add the first reagent to the Fe(NO 3 ) 3 in the test tube. 12. What ion was added to the test tube? SCN What color did the solution turn? Deep red 14. What compound was formed? FeSCN Did the equilibrium shift to the right or to the left? right I will add the second reagent to the test tube. 16. What color did the solution turn? Any other observations? Yellow with a white precipitate 17. Did the equilibrium shift to the right or to the left? left 18. Which of these reagents was added? a. Fairy Dust b. H 2 O c. HCl d. AgNO 3

8 School: Dissolution of NH 4 Cl Equilibrium There is a test tube on your table or hood containing a saturated solution of ammonium chloride. One of your team members will hold the test tube (WITH GLOVES ON) after I add a few drops of concentrated HCl. Note your observations here: Ammonium chloride crashes out, and the test tube is warm Next, another team member will hold a test tube containing ammonium chloride crystals. I will add water to the test tube. Note your observations here: The crystals dissolve and the test tube is cold Write the chemical equation for the dissolution of ammonium chloride: NH 4 Cl NH Cl - Is the dissolution of ammonium chloride exothermic or endothermic? Endothermic

9 School: Chemistry Quick Quiz Answer the following questions to the best of your ability. You might not finish before the time limit. Good luck! The questions on this quiz are from Principles of Chemistry: a Molecular Approach by Nivaldo J. Tro, the textbook used by Edgewood College general chemistry students. 1. For the reaction shown, calculate how many moles of NO 2 form when 10.5g of N 2 O 2 completely reacts. Number of moles of NO 2 : 9.40 mol 2 N 2 O 2 (g) 4 NO 2 (g) + O 2 (g) 2. Lead ions can be precipitated from solution with KCl according to the reaction below. When 28.5g KCl is added to a solution containing 25.7g Pb 2+, a PbCl 2 precipitate forms. The precipitate is filtered and dried and found to have a mass of 29.4g. Determine the limiting reactant, theoretical yield of PbCl 2, and percent yield for the reaction. Pb 2+ (aq) + 2 KCl(aq) PbCl 2 (s) + 2 K + (aq) Limiting reactant: Pb 2+ Theoretical yield PbCl 2 : 34.5g Percent yield PbCl 2 : 85.3% 3. A cylinder contains 28.5L of oxygen gas at a pressure of 1.8 atm and a temperature of 298K. How much gas (in moles) is in the cylinder? Number of moles of gas: 2.1 mol

10 4. Consider the chemical reaction below. How many liters of hydrogen gas are formed from the complete reaction of 15.7g C? Assume that the hydrogen gas is collected at a pressure of 1.0 atm and a temperature of 355K. Liters of hydrogen gas: 38L C(s) + H 2 O(g) CO(g) + H 2 (g) 5. Classify the following reactions (i.e. acid/base, redox); one of these could be classified as two types: K 2 CO 3 (aq) + NiCl 2 (aq) NiCO 3 (s) + 2 KCl(aq) precipitation H 2 SO 4 (aq) + 2KOH(aq) 2 H 2 O(l) + K 2 SO 4 (aq) acid/base 4 Fe(s) + 3 O 2 (g) 2 Fe 2 O 3 (s) redox CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g) combustion, redox 6. Predict the products of the following reactions and balance them. If no reaction occurs, write no reaction : LiI(aq) + BaS(aq) no reaction KCl(aq) + CaS(aq) no reaction CrBr 2 (aq) + Na 2 CO 3 (aq) CrO 3 (s) + 2 NaBr (aq) NaOH(aq) + FeCl 3 (aq) Fe(OH) 3 (s) + 3 NaCl (aq)

EXPERIMENT 4 THE EFFECT OF CONCENTRATION CHANGES ON EQUILIBRIUM SYSTEMS

EXPERIMENT 4 THE EFFECT OF CONCENTRATION CHANGES ON EQUILIBRIUM SYSTEMS PURPOSE In this experiment, you will look at different equilibria, observe how addition or removal of components affects those equilibria and see if the results are consistent with Le Chatelier's principle.