Acid Strength Answers

Acid Strength Answers - Acid Strength Module General...

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Acid Strength Module – General Chemistry II CHE141 - GENERAL CHEMISTRY II Module developed by: David L. Cedeño Acid Strength and Molecular Structure Introduction The strength of an acid is related to its molecular structure. For instance, you know that HCl, HBr, and HI are strong acids, while HF is a weak one. Have you wonder why? Would you be able to tell if HI is stronger than HBr and HCl? The strength of an acid in aqueous media is related to its ability to transfer a proton to water. Such ability is related to the how strong the proton is held by the rest of the molecule (i.e. the bond strength) and the thermodynamic stability of the resulting conjugated base. In this project you will calculate the enthalpy change ( H) involved in the proton transfer dissociation of the acid (say HA) according to: HA(g) + H 2 O(g) H 3 O + (g) + A (g) Note that the reaction H is expressed for all reactants and products in the gas phase, but this is for simplicity because our software cannot model molecules in aqueous solutions. The results as you will see are quite valid. You will explore two series of acids: the haloacids (HF, HCl, HBr, and HI) and the chlorinated oxyacids (HClO, HClO 2 , HClO 3 , and HClO 4 ) and will make predictions based on your observations. You are encouraged to review the following material in your textbook: Section 16. (Acid strength and structure) Objectives: To understand how the structure and electronic factors in an acid influence the bond strength. Materials: You will need Argus Lab 4.0 to carry out the molecular modeling and calculation of DH for proton transfer. If you do not have Argus, a file is provided which contains all the results you would obtain using Argus.
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