in both beakers. The mixtures are stirred well, and the oil and water layers are allowed to separate. a. What is the predominant form of HIn in the aqueous buffer in beaker Y, the acid form or the conjugate base form? Explain your reasoning. b. In beaker X the oil trial is yellow, whereas in beaker Y the oil layer is colorless. Explain these observations in terms of both acid-base equilibria and interparticle forces. a. The conjugate base form, In(aq), is the predominant form of the indicator in the aqueous pH 7 buffer in beaker Y. This is because the pH is greater than the pKa of HIn, causing the equilibrium to form a significant amount of products, In-(aq) and H3O+(aq) 1 is earned for correctly identifying In (aq) as the predominant form in the aqueous layer in beaker Y because the solution is not acidic (may be implicit). 1 point is earned for stating that pH > pKa and that this causes the equilibrium to favor the products. b. At pH 3, the acid form HIn(aq) predominates in the aqueous layer of beaker X because pH < pKa. Since HIn(aq) is a neutral molecule, some of it can dissolve in the oil layer of beaker X because of London dispersion interactions with the oil, causing the oil layer to be yellow. In-(aq) is charged, it will preferentially dissolve in the aqueous layer of beaker Y because of ion-dipole interactions with the water, leaving the oil layer colorless. 1 point is earned for explaining the yellow color in the oil layer of beaker X in terms of acid-base equilibrium and interparticle forces between HIn molecules and oil molecules. 1 point is earned for explaining the colorless oil layer of beaker Y in terms of interparticle forces between In- ions and water molecules. 2010 Q5 5. Use the information in the table below to respond to the statements and questions that follow. Your answers should be in terms of principles of molecular structure and intermolecular forces. a. Draw the complete Lewis electron dot diagram for ethyne in the appropriate cell in the table above.
in both beakers. The mixtures are stirred well, and the oil and water layers are allowed to separate. a. What is the predominant form of HIn in the aqueous buffer in beaker Y, the acid form or the conjugate base form? Explain your reasoning. b. In beaker X the oil is yellow, whereas in beaker Y the oil layer is colorless. Explain these observations in terms of both acid-base equilibria and interparticle forces. a. The conjugate base form, In(aq), is the predominant form of the indicator in the aqueous pH 7 buffer in beaker Y. This is because the pH is greater than the pKa of HIn, causing the equilibrium to form a significant amount of products, In-(aq) and H3O+(aq) 1 is earned for correctly identifying In (aq) as the predominant form in the aqueous layer in beaker Y because the solution is not acidic (may be implicit). 1 point is earned for stating that pH > pKa and that this causes the equilibrium to favor the products. b. At pH 3, the acid form HIn(aq) predominates in the aqueous layer of beaker X because pH < pKa. Since HIn(aq) is a neutral molecule, some of it can dissolve in the oil layer of beaker X because of London dispersion interactions with the oil, causing the oil layer to be yellow. In-(aq) is charged, it will preferentially dissolve in the aqueous layer of beaker Y because of ion-dipole interactions with the water, leaving the oil layer colorless. 1 point is earned for explaining the yellow color in the oil layer of beaker X in terms of acid-base equilibrium and interparticle forces between HIn molecules and oil molecules. 1 point is earned for explaining the colorless oil layer of beaker Y in terms of interparticle forces between In- ions and water molecules. 2010 Q5 5. Use the information in the table below to respond to the statements and questions that follow. Your answers should be in terms of principles of molecular structure and intermolecular forces. a. Draw the complete Lewis electron dot diagram for ethyne in the appropriate cell in the table above. trial
new_exam_review_packet_-_teacher_version1-2.docx