Having a horrible time with my post lab! I need help with parts C, and D. If you

Question

Having a horrible time with my post lab! I need help with parts C, and D. If you could be sure to include how it relates to Le Chatelier's principle, that would be great. This part is confusing me.

Part C - Initial color was purple. When H2O was added it turned pink. With a hot bath it turned back purple. With a ice bath it went back to pink.

Part D - Mixed bromothymol blue turned from green to orange when HCl was added. With NaOH added it turned green. More NaOH turned it blue.

Attached are the proceedure and questions

Explanation / Answer

Part C)

Conversion of CoCl4^2- (purple) to Co(H2O)6^2+ (pink) is an exothermic reation, such that heat is given off from the reaction. Conevrsion of Co(H2O)6^2+ (pink) to CoCl4^2- (purple) is an endothermic reaction, so heat is taken in to perform this reaction.

For an exothermic reaction, when heat is taken out, the reaction would proceed in the direction so as to balance that (increase) the heat of reaction, or to bring it to the original equilibrium state. This is according to LeChatelliers principle. The step from CoCl4^2- to Co(H2O)6^2+ being a exothermic reaction, when heat is removed the reaction goes in forward direction, more of Co(H2O)6^2+ is formed.

On the other hand for an endothermic reaction, such that as heat is supplied by heating is water bath, the excess heat is balanced by conversion to CoCl4^2-. This is again by LeChatellier's principle. Heat is balanced by reaction going in the forward direction.

Part D)

Bromothymol blue is an indicator. It turns orange in acidic medium by addition of HCl, here it is in fully protonated form. When base NaOH is added, it deporotnates to give green coloration, which upon further addition of more NaOH (OH)-) pushes the reaction for complete consumption of OH- added in to more blue color (more basic solution). That is more indicator is deprotonated. This is according to LeChatellier's principle.

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.