1 / 34

water and pH

water and pH. Dr. Wesal.A.elHanbli. The human body is composed of over 70% water, and it is a major component of many bodily fluids including blood, urine, and saliva .

yaron
Télécharger la présentation

water and pH

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. water and pH Dr. Wesal.A.elHanbli

  2. The human body is composed of over 70% water, and it is a major component of many bodily fluids including blood, urine, and saliva. • Water is distributed in the human body between the intracellular compartment and extracellular compartment (intravascular and interstitial compartments) .

  3. Physical and chemical properties of water: • High melting point • High boiling point…. • dipolarity

  4. The total atomic weight of 18 daltons. • The structure of the electrons surrounding water is tetrahedral, resembling a pyramid.

  5. This means that even though the oxygen in water is bound to each of the hydrogens by a covalent bond (sharing a pair of electrons), the oxygen "pulls" the shared electrons closer to itself. • This unequal sharing of the electrons in the O-H bond in water causes the hydrogens to have a partial positive charge (positive dipole), and the oxygen has a partial negative charge (negative dipole). • Water is called dipolar molecule because it has a positive side and a negative side.

  6. Water molecules are attracted to each other, like the positive and negative ends of a magnet making water very dense (hydrogen bonds).

  7. On average, a liquid water molecule will have 3 out of 4 possible hydrogen bonds. • This is because the molecules in liquid are in constant motion. • In ice, water will form all 4 possible hydrogen bonds because the molecules in a solid are essentially locked in place.

  8. Water is a good solvent • The positive side of water (hydrogen) surrounds negatively charged molecules, and the negatively charged side of water (oxygen) surrounds positively charged molecules .

  9. Water cannot dissolve oil. • This is because oily substances are non-polar. Non-polar substances (which lack dipoles) are also called hydrophobic(water fearing).

  10. Ionization of Water and the pH • H2O H+ + OH-

  11. How much H+ and OH- exist in water? Very, very little! • The ratio of either H+ or OH- to H2O in neutral water is 1:1,000,000,000! • Since this is such a small amount of either H+ or OH-, they rarely meet and neutralize each other

  12. The equilibrium constant, Keqdescribes the ionization equilibrium of water: • Keq = [H+][OH-]

  13. For neutral water, the Keq is 1 x 10-14 M and the concentrations of [H+] and [OH-] are each 1 x 10-7 M . • Let's look at that last number • 0.0000001 M

  14. This is obviously a very small number. • A more manageable way to discuss small numbers such as this is to take the negative logarithm. • For thenegative logarithm of [H+], this is called the pH. • In this case: • -log(0.0000001 M) = 7

  15. The pH of a solution is simply the negative logarithm of [H+]. • The pH of a solution describes the acidity of a solution. • Acidic solutions are those with a pH of less than 7 and basic solutions have a pH greater than 7. • A solution, like H2O, with a pH = 7 is neutral.

  16. In the body, the pH of the blood is 7.4 • This corresponds to [H+] of about 40 nM. • This value can only vary from 37nM to 43nM without serious metabolic consequences. (PH 7.35 - 7.45).

  17. what is the pKa ? • In living systems, much of the chemistry involves interactions between acids and bases. • Acids are H+ donors and bases are H+ acceptors. • HA H+ + A-

  18. How readily an acid gives up its H+ is expressed by the acid dissociation constant, or Ka: • Ka = [H+][A-] / [HA]

  19. Equation can be rearranged to: • [H+] = Ka ([HA] / [A-] ) • and by taking the log10 of both sides and multiplying each side by -1, we get: • -log10[H+] = -log10Ka - log10 ([HA] / [A-] )

  20. pH = pKa + log10 ([A-] / [HA] ) • The pKa is the negative logarithm of the Ka. • This equation is known as the Henderson-Hasselbach equation

  21. What is a buffer? • A buffer is a solution that resist changes in pH • It is a molecule that tends to either bind to or release hydrogen ions in order to maintain a particular pH eg in blood It is 7.4. 

  22. Thus, a buffer can either accept or donate hydrogen ions, depending on the solution they are in.  • Since the buffers will accept hydrogen ions in acids and donate hydrogen ions in bases, there must be some in-between-pH where they hit an equilibrium point and do not prefer to either accept or donate hydrogen ions.  • That intermediate point, equilibrium, is the pH that the buffer tends to maintain.   

  23. There are three important buffer systems in our bodies: • bicarbonate buffer system • phosphate buffer system • protein buffer system

  24. All three work similarly-- if they find themselves in a solution with a lot of free hydrogen ions floating around (an acid), they act as bases and suck up the excess hydrogen ions.  • And if they find themselves in a solution lacking free hydrogen ions (a base), they donate their hydrogen ions to the solution.

  25. Acidosis and alkalosis • In a normal subject the pH is maintained between 7.35 - 7.45. • Any increase in pH will result in alkalosis (after excessive vomiting) • Any decrease in pH will result in acidosis ( in complicated type I diabetes diabetic ketoacidosis)

  26. THANKS

More Related