Experiment-6-heheh.docx

Mapua University Senior High School STEM 12 Experiment 6: Le Châtelier’s Principle Toriaga, Jose III., Ipio, Zymond Kiel D., Alviz, Jude Lorenz D., Onia, John Jubert E., Frias, Cairon John B. G217

Abstract: Le Chatelier's Principle states that if a system is at equilibrium and something is changed so that it is no longer at equilibrium, the system will respond in an effort to counteract that change. If more reactant is added, the equilibrium will shift forward in order to consume some of the extra reactant, resulting in more products. If some of the product is removed from the system, the equilibrium will shift forward to produce more of that product. The equilibrium can be shifted reverse by either adding product to or removing reactant from the system. The experiment illustrated and demonstrated different situations where Le Châtelier’s Principles can be applied.

Introduction: Not all reactions go to completion, or use up all of one of the reactants. In some chemical reactions there is always some amount of products and some reactants present. In these chemical systems two competing processes are occurring, the forward reaction and the reverse reaction of that system. Both the forward and the reverse reactions are taking place simultaneously. When the rate of the forward reaction equals the rate of the reverse reaction, the system is at equilibrium. The concentrations of the products and reactants remain constant. That is not to say that the system is static. Both reactions are occurring and are doing so at the same rate, so there is no net change in the concentrations of the reactants or of the products. When writing an equation for a reaction at equilibrium a double headed arrow (↔) or double arrows pointing in opposite directions (⇄) is used. These designations indicate that both the forward and reverse reactions are occurring at the same time.

Methodology & Procedures: List of chemicals to be used: Quantity needed per group 10 drops 10 drops

Concentration

Name of chemicals

Chemical Formula

1M 0.1 M

K2CrO4 NH4OH

5 drops 5 drops 2 mL 4 mL 3 mL 3 mL 3 mL

6M 1M 12M 5.4M 3M 0.1M 0.1M

Potassium chromate Ammonium hydroxide Hydrochloric acid Ammonium chloride Hydrochloric acid Sodium chloride Hydrochloric acid Ferric nitrate Potassium thiocyanate Potassium nitrate Acetic acid Sodium acetate Methyl orange Phenolphthalein

0.5g 10 drops

0.1M 0.1M

HCl NH4Cl HCl NaCl HCl Fe(NO3)3 KSCN KNO3 HC2H3O2 NaC2H3O2

List of apparatus to be used: Quantity

Name of apparatus

6pcs.

Test tubes

1 pc.

150-ml beaker

1 pc.

Medicine dropper

1 pc.

50-ml graduated cylinder

6pcs.

Micro test tubes

1 pc.

10-mlgraduated cylinder

1 pc.

Glass string rod

1 pc.

Dropper

1. Chromate – Di Chromate Equilibrium A micro test-tube is filled with 10 drops of potassium chromate and was added by 6M of Hydrochloric acid drop wise until the color is changed and was observed and recorded for its change in color. Add a drop wise of 6M sodium hydroxide, NaOH, until there is a change

in color. Again, add 6M of hydrochloric acid until the color of the solution change. Record every change in color. 2. Thiocyanatoiron(III) Complex Ion Equilibrium A solution will be prepared using a 10mL graduated cylinder to measure 3mL of 0.1M of ferric nitrate mixed with 3 mL of 0.1M of Potassium thiocyanate and will be diluted by adding 50mL of distilled water. The solution will be placed in a 150 mL beaker. After preparing the solution, arrange then test tubes and label them from A - F. Fill them with 5mL of the solution prepared in the 150mL beaker. Test tube A will be added with 1mL of 0.1M of ferric nitrate. Test tube B will be mixed with a 1mL of potassium thiocyanate. 0.5 grams of potassium nitrate will be added on test tube C. Test tube D will be placed in a boiling water while test tube E will be placed on an ice bath both for two minutes. While test tube F will be mixed with 1 mL of distilled water and will serve as your reference solution. Compare the intensity of the red color of the solution in each test tube to the reference solution. Record the observation.

3. Weak acid Equilibrium (Ionization of Acetic Acid) A micro test tube will be prepared and will be filled with 10 drops of 0.1M of acetic acid. Add a drop of methyl orange and observe the change in color. Add a few drops of 1.0M sodium acetate until there is a change in color. Observe the change in color every different chemical is mixed with the solution and record the observation.

4. Weak Base Equilibrium (ionization of Ammonia) 10 drops of 0.10M of ammonium hydroxide will be placed in a micro test tube. Add a drop of Phenolphthalein and observe the change. Lastly put a drop wise of 1.0M ammonium chloride until there is a change in color. Observe and record. 5. Saturated Salt (Sodium Chloride) Equilibrium In a test tube place 4ml of 5.4M Sodium Chloride. Add 2 ml of 12M of hydrochloric acid. Observe and record it.

Results and Discussion: Gathered Data & Observations. 1. Chromate – Di Chromate Equilibrium Solution

Observation (color of the solution) Yellow Orange Yellow Orange

K2CrO4 K2CrO4 + HCl K2CrO4 + HCl + NaOH K2CrO4 + HCl + NaOH + HCL

Adding HCl, HCl will increase the concentration so the reaction will be shifted to the left side, accordingly acetate ions concentration will decrease. If we add NaOH, NaOH, this will increase water concentration so the reaction will be shifred to the right side accordingly increasing the concentration of acetate ions. Meaning HCl increases the concentration making it darker in color (orange) while when NaOH is added, it will result to increase in water concentration resulting to a lighter color (yellow). 2. Thiocyanatoiron(III) Complex Ion Equilibrium

Solution Test Tube A + Fe(NO3)3 Test Tube B + KSCN Test Tube C + KNO3 Test Tube D in boiling water Test Tube E in ice bath

Darker or Lighter than the reference solution (test tube F) Darker Darker Lighter Lighter Darker

The double-headed arrow shows that the reaction is reversible. Initially, when the concentrations of A and B are much higher than the concentration of C, the forward reaction rate is much faster than the reverse reaction rate. However, when enough C is formed and A and B consumed, the rate at which A and B are disappearing slows down and becomes the same as the rate at which A and B are being formed by the reverse reaction.

3. Weak acid Equilibrium (Ionization of Acetic Acid)

Solution

Observation (color of solution)

HC2H3O2 + methyl orange HC2H3O2 + methyl orange + NaC2H3O2

Red Golden yellow

By adding a component of the right side the equilibrium is shifted to the left (Le Chateliers principle) and that's is in this case the acid.

4. Weak Base Equilibrium (ionization of Ammonia)

Solution NH4O4 + Phenolphthalein NH4O4 + Phenolphthalein + NH4Cl

Observation (color of solution) Pink White / Colorless

According to Le Chatlier's principle adding more NH4+ ions from the NH4Cl adds it to the right side of the equilibrium making it pink. But to lessen that, adding NH4Cl, the reaction shifts to the left, taking the OH- with it so when the amount of pinkness lightens up, and making the solution to light pink until it clears up making it colorless.

5. Saturated Salt (Sodium Chloride) Equilibrium If you add HCl solution to a saturated NaCl solution, you will drive the equilibrium back to the left by increasing the concentration. As a result, NaCl will re-crystallize in the solution.

Conclusion: Any system at equilibrium will remain at equilibrium unless the conditions of the system change. Le Châtelier’s principle states that a system at equilibrium will respond to a stress on the system in such a way so as to relieve the stress and establish a new equilibrium. The system will have one reaction dominate until the offsetting changes allow the rates of the forward and reverse reactions to be equal again. If the forward reaction dominates in order to

offset the changes, we say the system “shifts to the right” or “shifts toward products” in order to re-establish equilibrium conditions.

References: Chang, Raymond(2006). General Chemistry: The Essential Concepts, 9th Edition. McGrawHill, New York Slowinski, E.J., Woseley, W.C, and Masterson, W.L (2005). Chemical Principles in the Laboratory, 8th Edition Brooks/Cole Publishing Co., USA. Nelson,J.H. and Kemp,K.C.(2003). Chemistry: The Experiments), 9th Edition. Pearson Education,Inc., USA

Central

Science

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Szafran, Z., Pike, R. M., and Foster, J. C. (2003). Microscale General Chemistry Laboratory 2nd Edition. John Wiley and Sons, Inc., USA