Water and the aqueous systems DR. MALIK ALQUB MD. PHD.
The Water • The water constitutes 60-90% of living organisms • The water is an efficient solvent • The chemical reactions occur in water • The structure of biomolecules depends on water; ex. proteins, DNA.
The Water Molecule • Each O-H bond is highly polar, because of the high electronegativity of the oxygen • bond angle = 105 o • due to the bent shape, the O-H bond polarities do not cancel. This means water as a whole is polar.
The Water Molecule Water molecules are attracted to one another by hydrogen interactions This hydrogen bonding gives water: high surface tension .
Solvents and Solutes • Solution - a homogenous mixture, that is mixed molecule by molecule; made of: a Solvent - the dissolving medium a Solute - the dissolved particles
Concentrated vs. Dilute Lots of solute, but little solvent Lots of solvent, but little solute
Aqueous Solutions • Water dissolves ionic compounds and polar covalent molecules very well. • The rule is: “like dissolves like” • Polar dissolves polar. • Nonpolar dissolves nonpolar. • Oil is nonpolar. • Oil and water don’t mix. • Salt is ionic- makes salt water.
The Solution Process • Called “solvation”. 1) breaks the + and - charged pieces apart, and 2) surrounds them.
H H H H O O O H H H H O O H H O O H H H H H H O H O H How Ionic solids dissolve in water These ions have been pulled away from the main crystal structure by water’s polarity. These ions have been surrounded by water, and are now dissolved!
Electrolytes • Electrolytes- compounds that conduct an electric current in aqueous solution, or in the molten state • all ionic compounds are electrolytes because they dissociate into ions (they are also called “salts”)
Extracellular and Intracellular Fluids • Extracellular fluids • Sodium is the chief cation • Chloride is the major anion • Intracellular fluids have low sodium and chloride • Potassium is the chief cation • Phosphate is the chief anion
Acids and Bases • Acid – increases the [H+] of a solution • Base – decreases the [H+] of a solution • May form OH- ion or absorb H+ ions • Strong acid/base • Weak acid/base
The Buffer • What do we mean by BUFFER
Carbonic Acid – Bicarbonate Buffer System Respiratory component Renal component CO2 +H2O H2CO3H + + HCO3– (H2CO3 is a ‘volatile’ acid as CO2 exhaled ) Principal buffer system in the body. Provides 95% of buffering capacity in plasma.
The importance of pH control • The pH of the ECF remains between 7.35 and 7.45 • If plasma levels fall below 7.35 (acidemia), acidosis results • If plasma levels rise above 7.45 (alkalemia), alkalosis results • Alteration outside these boundaries affects all body systems • Can result in coma, cardiac failure, and circulatory collapse
Weak acids - HA H + A + Weak acids Conjugate base
Henderson–Hasselbalch equation - + HA H + A Ka , acid dissociation constant (also known as acidity constant, or acid-ionization constant)
Henderson–Hasselbalch equation log log log log
Henderson–Hasselbalch equation X log log + log log log
Henderson–Hasselbalch equation - - + log log pKa = -log Ka pH = -log
Titration a method of estimating the amount of solute in a solution. The solution is added in small, measured quantities to a known volume of a standard solution until a reaction occurs, as indicated by a change in color or pH or the liberation of a chemical product
Titration of acetic acid OH- H2O CH3COO− + H+ CH3COOH OH- added pKa = 4.8 pH 3 4 5 6 7
Imagine PKa 9.8 PKa 2.3 Carboxyl group Amino group acidic Basic
Isoelectric point PKa 9.8 PKa 2.3 Isoelectric point Carboxyl group Amino group Isoelectric point Acidic +1 Basic -1