Lab 2: Le Chatelier's Principle

Purpose / IntroductionThe intention of this lab is to determine the effect(s) a change has on a system of

equilibrium. The changes will then be related to Le Chatlier's Principle: a system under stress will correct itself to relieve the system and bring it back to equilibrium. From the gathered change observations, the equilibrium concept will be defined in relation to Le Chatlier's Principle.

For this lab, it is safe to assume that there will be equilibrium shifting between the reactants and products when certain solutions are added to the systems. Depending on the direction of the shift, the reaction can be determined to be either endothermic or exothermic. In Part I, I expect adding HCl will cause in a shift to the right because acids remove hydroxides. As for adding Na2 EDTA , I am unsure of the possible reactions. For Part II, mixing solid Na2 SO4 crystals into the solution should result in an equilibrium shift to the left because more S O4

2−¿¿ is being added to the already existing amount in the mixture. And, finally when NaHSO4 is added, I believe the shift will be to the right instead because HS O4 does not preexist in the mixture.

Prelab QuestionsN/A

ProcedureRefer to CHE 112-BK01 lab manual

Lab 2: Le Chatelier's Principle (page 27)

Data / ResultsPart I

Change to the Mixture Observed changesAdd 5 drops 2.0 M MgCl2 to wells 1 & 2 Colorless and precipitate-less

Add 10 drops 2.0 M MgCl2 to wells 3 & 4 Colorless and precipitate-lessAdd 1 drop phenolphthalein to all wells Mixtures become milky whiteAdd 5 drops 1.0 M NaOH to all wells Mixtures change color to magenta/hot pink and the precipitate

thickensAdd 1 drop 6.0 M HCl to well 1 Mixture returned to previous milky white color and the precipitate

thins outContinue to add HCl until color change Remains white after one drop of HCl

Add 1 drop 0.15 M Na2 EDTA to well 2 Mixture briefly returns to milky white before quickly going back to magenta/hot pink color

Continue to add NA2 EDTA until color change

6 drops for the mixture to stay milky white for a longer period of time before changing back to magenta/hot pink11 drops maintains the milky white color but solid precipitate remains pink

Place well 3 in hot water bath (36℃) Mixture becomes less viscous and turns a lighter shade of pinkPlace well 4 in cold water bath ¿) Mixture becomes more viscous and no color change is observed

Postlab QuestionsA. The equilibrium will shift to the right when HCl is added to solid Mg (OH )2. The shift is due to the HCl taking up the hydroxides. B. The addition of Na2 EDTA will cause the equilibrium to shift to the right as well because the concentration of Mg2+¿¿ will decrease.C. This is an endothermic reaction. The reaction requires energy to break the ions apart from the crystal lattice structure.

Part IIChange to the Mixture Observed changes

Add 5 drops 0.1 M NaHSO4 to wells 1, 2, & 3 Colorless and precipitate-less

Add 10 drops 0.1 M NaHSO4 to wells 4 & 5 Colorless and precipitate-lessAdd 1 drop thymol blue indicator to all wells Light baby pink color and no precipitate formedAdd 1 drops 1.0 M Na2 SO4 to well 1 Lighter "blushy salmon" pink color, no precipitate formed

Continue to add Na2 SO4 until color change 3 drops causes the color to become a faint "skin tone" orange

Add few solid crystals of Na2 SO4 to well 3 Mixture turns lavender purple and remains precipitate-less

Continue to add NA2 SO 4 crystals until color change

Color remains a lavender purple and does not create a precipitate

Place well 4 in hot water bath (34℃) Mixture turns "candy apple" red30℃ The "candy apple" red color faded to a lighter shade of red

Place well 5 in cold water bath ¿) Mixture turns magenta pink2℃ Magenta pink color changed to a bright hot pink shade

Postlab QuestionsA. The equilibrium will shift to the left when Na2 SO4 is added to the reactants. Na2 SO4 is a salt, and when it dissociates, the reaction needs to shift the equilibrium to the left to "abosrb" the extra salts.B. When NaHSO4 is added to the reactants the equilibrium will shift to the right. Although NaHSO4 is a salt like Na2 SO4, NaHSO4 dissociates into Na+¿¿ and HSO4

−¿¿, and

the shift to the right will "absorb" the extra HSO4−¿¿

.C. This is an exothermic reaction because acid added to water has a strong reaction.

Conclusion The results from this lab displayed results that agreed with my expected results. In the first part, the equilibrium shifted to the right when HCl was added to the system. Additionally, in the second part of the lab, the equilibrium shifted to the left when the solid Na2 SO4 crystal was mixed in the system. And finally, the last equilibrium shifted to the right when NaHSO4 was added to the system.

The result that I was unsure of –adding Na2 EDTA to a system– displayed a result with the equilibrium shifting to the right.