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ABC’s of pH. Acids and Bases. Revised 10-03-2006. Homeostasis. Chemical reaction in the body are very sensitive to changes in pH. pH values in Body. Gastric Juices 1.2 - 3.0 Urine 4.6 – 8.0 Saliva 6.35 - 6.85 Blood 7.35 – 7.45 Spinal Fluid 7.4 Pancreatic Juice 7.1 – 8.2
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ABC’s of pH Acids and Bases Revised 10-03-2006
Homeostasis • Chemical reaction in the body are very sensitive to changes in pH.
pH values in Body • Gastric Juices 1.2 - 3.0 • Urine 4.6 – 8.0 • Saliva 6.35 - 6.85 • Blood 7.35 – 7.45 • Spinal Fluid 7.4 • Pancreatic Juice 7.1 – 8.2 • Bile 7.6 – 8.6
pH • pH is based on the relative concentration of hydrogen ions (H+ or H3O+) in a solution. Water ionizes into H+ and OH- H2O H3O++ OH-
Scientists measure the pH of solutions using a pH meter The meter reads the H+ ion concentration in solution indicating the pH of the solution.
Mathematically it is • pH is based on the relative concentration of hydrogen ions in a solution. pH = -log [H+] • Water at 25oC contains 1/10,000,000 mole of H+ ions = 10 -7 moles/liter pH = -log [10-7] pH = 7
logarithmic • a pH of 6 is ten times more acidic than distilled water. • Also, a solution that has a pH of 8 is ten times more basic (alkaline) than distilled water. • Likewise, a solution that has a pH of 4 is 100 times more acidic than one which has a pH of 6.
The pH scale is logarithmic (that's what the "p" stands for; the "H" is short for hydrogen); • therefore, a solution that has a pH of 6 is ten times more acidic than distilled water. • Also, a solution that has a pH of 8 is ten times more basic (alkaline) than distilled water. • Likewise, a solution that has a pH of 4 is 100 times more acidic than one which has a pH of 6.
Properties of Acids • Substances with a pH below 7 are acids. • An acid is any substance that ionizes (release charged particles when dissolved) in water to produce H+ hydrogen ions or free protons in water. • Acids tend to taste sour. • Change blue litmus paper to red. • React with metals to release hydrogen gas. • Neutralize bases, forming water and salts • Acidic solutions have concentrations of H3O+ above 1 X 10-7
Acid Examples stomach juices hydrochloric acid HCl H+ + Cl- battery acid sulfuric acid H2SO4 2H+ + SO42- vinegar acetic acid CH3COOH H+ + CH3COO-
Measuring Acidity • Added acids increase [H3O+] • In acid solutions [H3O+] > 1 x 10-7 M • pH scale measures acidity without using exponential numbers.
Acid pH Calculations • [H3O+]=1 x 10-5M, pH = ? • 5 (acidic) • [H3O+]=2.6 x 10-5M, pH = ? • 4.59 (acidic) • [H3O+]=7.8 x 10-3M, pH = ? • 2.11 (acidic)
Properties of Bases • have a pH greater than 7. • A base is a substance that ionizes in water solution to produce OH- hydroxide ions. • Bases tend to feel slippery to the skin. • Bases accept protons • Bitter taste • Bases turn red litmus paper blue. • Neutralize acids, forming water and salts. • Basic solutions have H3O+ concentrations less than 1 X 10-7
Base Examples Milk of Magnesia Mg (OH)2 2OH- + Mg2+ Mylanta Mg (OH)2 + Al(OH)3 5OH- + Mg2+ + Al3+ Maalox Mg (OH)2 + Al(OH)3 5OH- + Mg2+ + Al3+
Measuring Acidity • Added bases increase [OH-]. • In basic solutions [OH-] > 1 x 10-7 M [H3O+] < 1 x 10-7 M • pH scale measures acidity without using exponential numbers.
Base pH Calculation[H3O+] to ph • [H3O+]=1 x 10-10M, pH = ? • 10 (basic) • [H3O+]=6.3 x 10-9M, pH = ? • 8.20 (basic) • What if the number is not 1?
pH Calculations • pH to [H3O+]? • inverse log of negative pH • orange juice, pH 3.5 [H3O+]=? • [H3O+] = 10-3.5 = 3.2 x 10-4 M • saliva, pH 6.2 [H3O+]=? • [H3O+] = 10-6.2 = 6.3 x 10-7 M
Strong and Weak Acids and Bases • Strong acids ionize completely in water • Weak acids ionize only partially in water • Strong bases ionize completely in water. • Weak bases ionize only partially in water.
Neutralization • Acids and bases can neutralize each other by forming water and salt. • Salt - a crystalline compound composed of the negative ion of an acid and the positive ion of a base. H+A- + B+OH-H20 + A-B+(salt)
Examples Stomach acid + Milk of Magnesia H20 + salt Hydrochloric Acid + Magnesium Hydroxide H20 + salt 2HCl + Mg(OH)2 2H20 + MgCl2 Stomach acid + Mylanta H20 + salt Hydrochloric Acid + Magnesium Hydroxide and Aluminum Hydroxide H20 + salt 5HCl + Mg(OH)2 and Al(OH)3 5H20 + MgCl2 + AlCl3
Buffer • Buffers act as a reservoir for hydrogen ions, donating or removing them from solution as necessary. • a solution that can receive moderate amounts of either acid or base without the significant change in its pH.
Buffer • A buffer is a mixture of a weak acid with the salt of the acid. • If small amounts of acid is added, hydronium ions are neutralized by reacting with the salt in solution • If small amounts of base is added, hydroxide ions are neutralized by reacting with the acid.
Protein Buffer System • Intracellular Fluid • Blood Plasma • Red Blood Cells • Hemoglobin • Blood Plasma • Albumin
Protein Buffer Systems • carboxyl group (—COOH) • amino group (—NH2);
Protein Buffer Systems • carboxyl group (—COOH) • Releases H+↑pH
Protein Buffer Systems • amino group (—NH2); • Forms NH3+ ↓pH
The protein hemoglobin is an important buffer of H+ in red blood cells. As blood flows through the systemic capillaries, carbon dioxide (CO2) passes from tissue cells into red blood cells, where it combines with water (H2O) to form carbonic acid (H2CO3). Once formed, H2CO3 dissociates into H+ and HCO3-.
At the same time that CO2 is entering red blood cells, oxyhemoglobin (Hb-O2) is giving up its oxygen to tissue cells. Reduced hemoglobin (deoxyhe-moglobin) is an excellent buffer of H+, so it picks up most of the H+. For this reason, reduced hemoglobin usually is written as Hb-H. The following reactions summarize these relations
Hemoglobin • Brown • 65,000 Daltons • 4 sub units
Carbonic Acid- Bicarbonate • Carbonic acid • H2CO3 • weak acid • Bicarbonate ion • HCO3- • weak base
Phosphate Buffering System • Intracellular Fluid • Cytosol • Kidneys
