Biology_ Acids and Bases.pdf

BIOLOGY: ACIDS AND BASES ACIDIC AND BASIC CONDITIONS AFFECT LIVING ORGANISMS Hydrogen Ion (H+) - A single proton with a Hydronium Ion (H3O+ ) - proton binds to charge of 1+ the other water molecule, making that...

BIOLOGY: ACIDS AND BASES ACIDIC AND BASIC CONDITIONS AFFECT LIVING ORGANISMS Hydrogen Ion (H+) - A single proton with a Hydronium Ion (H3O+ ) - proton binds to charge of 1+ the other water molecule, making that molecule a hydronium ion Hydroxide Ion (OH-) - Byproduct of a water molecule that lost a proton pH Scale - Used to describe how acidic or basic a solution is H+ and OH- are very reactive. - Changes in their concentrations can drastically affect a cell’s proteins and other complex molecules. Concentrations of H+ and OH- are equal in pure water, adding certain kinds of solutes, called acids and bases, disrupts this balance. ACID Acid - a substance that increases the hydrogen ion concentration of a solution When acids dissolve in water, they donate another H+ to the solution. This source of H+(dissociation of water is the other source) results in an acidic solution—one having more H+ than OH-. Ex: When hydrochloric acid (HCl) is added to water, hydrogen ions dissociate from chloride ions BASE A substance that reduces the hydrogen ion concentration of a solution Some bases reduce the H+ concentration directly by accepting hydrogen ions. Ammonia (NH3) - for instance, acts as a base when the unshared electron pair in nitrogen’s valence shell attracts a hydrogen ion from the solution, resulting in an ammonium ion (NH4+) Other bases reduce the H+ concentration indirectly by dissociating to form hydroxide ions, which combine with hydrogen ions and form water. One such base is sodium hydroxide (NaOH), which in water dissociates into its ions:  In either case, the base reduces the H+ concentration.Solutions with a higher concentration of OH- than H+ are known as basic solutions A solution in which the H+ and OH- concentrations are equal is said to be neutral. Hydrochloric acid - a strong acid and Sodium hydroxide - a strong base Ammonia is a weak base. ➔ The double arrows in the reaction for ammonia indicate that the binding and release of hydrogen ions are reversible reactions, although at equilibrium there will be a fixed ratio of NH4+ to NH3. Weak acids - acids that reversibly release and accept back hydrogen ions. An example is carbonic acid: THE PH SCALE In any aqueous solution at 25°C, the product of the H+ and OH- concentrations is constant at 10^-14. This can be written as: (The brackets indicate molar concentration.) ACIDS - Adds hydrogen ions to a solution - Removes hydroxide ions because of the tendency for H+ to combine with OH-, forming water. A BASE = opposite effect - increasing OH- concentration - reducing H+ concentration by the formation of water. If enough of a base is added to raise the OH- concentration to 10^-4 M, it will cause the H+ concentration to drop to 10^-10 M. Whenever we know the concentration of either H+ or OH- in an aqueous solution, we can deduce the concentration of the other ion. The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration: For a neutral aqueous solution, [H+ ] is 10^-7 M, giving us pH decreases as H+ concentration increases  A solution of pH 10 has a hydrogen ion concentration of 10^-10 M and a hydroxide ion concentration of 10^-4 M. The pH of a neutral aqueous solution at 25°C is 7, the midpoint of the pH scale. A pH value less than 7 denotes an acidic solution; the lower the number, the more acidic the solution. The pH for basic solutions is above 7. MOST biological fluids such as blood and saliva, are within the range of pH 6–8 digestive juice of the human stomach gastric juice, - pH of about 2. Each pH unit represents a tenfold difference in H+ and OH- concentrations. It is this mathematical feature that makes the pH scale so compact. ➔ A solution of pH 3 is not twice as acidic as a solution of pH 6, but 1,000 times (10 x 10 x 10) more acidic. The internal pH of most living cells ➔ close to 7 ➔ A slight change in pH can be harmful because the chemical processes of the cell are very sensitive to the concentrations of hydrogen and hydroxide ions. The pH of human blood is very close to 7.4, which is slightly basic. A person cannot survive for more than a few minutes if the blood pH drops to 7 or rises to 7.8, and a chemical system exists in the blood that maintains a stable pH. If 0.01 mol of a strong acid is added to a liter of pure water, the pH drops from 7.0 to 2.0. If the same amount of acid is added to a liter of blood, however, the pH decrease is only from 7.4 to 7.3. BUFFERS - allows biological fluids to maintain a relatively constant pH despite the addition of acids or bases. - A buffer is a substance that minimizes changes in the concentrations of H+ and OH- in a solution. It does so by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted. BUFFER SOLUTIONS - contain a weak acid and its corresponding base, which combine reversibly with hydrogen ions. - Several buffers contribute to pH stability in human blood and many other biological solutions. One of these is carbonic acid (H2CO3), which is formed when CO2 reacts with water in blood plasma. Carbonic acid dissociates to yield a bicarbonate ion (HCO3 - ) and a hydrogen ion (H+ ): The chemical equilibrium between carbonic acid and bicarbonate acts as a pH regulator, the reaction shifting left or right as other processes in the solution add or remove hydrogen ions. If the H+ concentration in blood begins to fall (that is, if pH rises), the reaction proceeds to the right and more carbonic acid dissociates, replenishing hydrogen ions. But when the H+ concentration in blood begins to rise (when pH drops), the reaction proceeds to the left, with HCO3 - (the base) removing the hydrogen ions from the solution and forming H2CO3. Thus, the carbonic acid–bicarbonate buffering system consists of an acid and a base in equilibrium with each other. Most other buffers are also acid- base pairs. Acidification: A Threat to our Ocean Among the many threats to water quality posed by human activities is the burning of fossil fuels, which releases CO2 into the atmosphere. The resulting increase in atmospheric CO2 levels has caused global warming and other aspects of climate change. About 25% of human-generated CO2 is absorbed by the oceans. Ocean Acidification When CO2 dissolves in seawater, it reacts with water to form carbonic acid, which lowers ocean pH. alters the delicate balance of conditions for life in the oceans As seawater acidifies, the extra hydrogen ions combine with carbonate ions (CO3 2- ) to form bicarbonate ions (HCO3 - ), thereby reducing the carbonate ioN concentration Scientists predict that ocean acidification will cause the carbonate ion concentration to decrease by 40% by the year 2100. This is of great concern because carbonate ions are required for calcification, the production of calcium carbonate (CaCO3) by many marine organisms, including reef-building corals and animals that build shells. The disappearance of coral reef ecosystems would be a tragic loss of biological diversity. If there is any reason for optimism about the future quality of water resources on our planet, it is that we have made progress in learning about the delicate chemical balances in oceans, lakes, and rivers. Continued progress can come only from the actions of informed Individuals, like yourselves, who are concerned about environmental quality. This requires understanding the crucial role that water plays in the suitability of the environment for continued life on Earth.