Acids & Bases I





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Published on Oct 6, 2010

This course is part of a series taught by Kevin Ahern at Oregon State University on General Biochemistry. For more information about online courses go to http://ecampus.oregonstate.edu/ http://www.youtube.com/playlist?list=...

Also check out the free textbook "Biochemistry Free and Easy" at: http://biochem.science.oregonstate.edu

1. Students are responsible for completely reading the syllabus and understanding what is in it.

2. Covalent bonds are VERY strong bonds that hold atoms/molecules together. Covalent bonds are the 'glue' that holds together biomolecules.

3. Hydrogen bonds are much weaker bonds that are also important in biological molecules. Hydrogen bonds arise from uneven sharing of electrons betweeen, for example a nitrogen and a hydrogen or an oxygen and a hydrogen. In each case, the hydrogen ends up with a partial positive charge and the other atom has a partial negative charge. The partial positive charge of the hydrogen may be attracted to a partial negative charge on another oxygen or hydrogen. These bonds are weaker than covalent bonds, but are VERY important in stabilizing protein and DNA structures.

4. Water has its relatively high boiling point due to its numerous hydrogen bonds. The double helix of DNA is held together by hydrogen bonds between the individual bases.

5. Thermodynamics is the study of energy. Understanding energy is essential for understanding any type of chemistry, including biochemistry. We shall discuss it later in the term.

6. pH is a measure of the proton concentration in a solution. The pH is the negative log of the hydrogen ion concentration. The lower the pH, the higher the hydrogen ion concentration and the stronger the acid. pH + pOH = 14. The pOH is the negative log of the hydroxide ion concentration. The pKa is, therefore, the negative log of the Ka. The lower the pKa for an acid system (such as the acetic acid system discussed in class), the stronger the acid is.

7. I shall use the term acid in such a system to refer to the molecule containing the most protons and the term salt to refer to the acid which has lost a proton. For the acetic acid system.

8. Acetic acid (HAc above) is a weak acid, meaning that it doesn't completely dissolve in water. HCl, by contrast is called a strong acid because it completely dissociates in water.

9. pH = -Log[H+], pOH = -Log[OH-], pKevinAhern = -Log[KevinAhern], pKa = -Log[Ka]

10. Ka is the acid dissociation constant. The larger the Ka, the stronger the acid. Consequently, the lower the pKa, the stronger the acid.

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