Acids & Bases Flashcards
Acids
A substance with a pH less than 7. An acid produces hydrogen ions, H+ in an aqueous solution. Hydrochloric acid (HCl) is a strong acid and dissociates in water. HCl > H+ + Cl-. Each H+ ion released is very reactive in aqueous solution it bonds to a water molecule. Product is known as Hydronium ion. Two reactions combined can give a following reaction. H+ + H20 > H30+.
Acid equation
HCl +H20> H30 + Cl- In this equation hydrochloric acid is donating a H+ to water. An acid can also be called a proton or hydrogen ion donor.
Acids in everyday life
The sour taste of fruits such as lemons is due to citric acid. Vinegar is aqueous solution of acetic acid. Acetic acid is a weak acid because it does not fully dissaociate or donate all its hydrogen ions. Human stomachs use hydrochloric acid to aid in digestion of proteins. HCl acid is strong acid because it fully dissociates in water.
Base
A substance with a pH greater than 7. A base can also be thought of as a proton acceptor. A base produces hydroxide ions, OH- in aqueous solution. Strong bases such as sodium hydroxide (NaOH) completely disassociates in water. One of the products is a hydroxide ion. NaOH > Na+ + OH-.
Base equation
NH3 +H20 <> NH4+ + OH- In the reaction of amonia (NH3) with water, amonia accepts a proton from water. Ammonia is acting as a base. Products are ammonium ion (NH4+) and OH-. Ammonia is a weak base because not every ammonia molecule present accepts protons and therefore the reaction is reversible.
Bases in everyday life
Bases taste bitter and feel slippery. They react with oils of the skin forming a soap like compound. Drain cleaners contain the base sodium hydroxide. Baking soda is a base used for cooking. Bicarbonate in pancreatic juice neutralizes stomach acid before the acidic chyme passes into the small intestine.
pH
A logarithmic scale based on the amount or concentration of hydrogen ions (H+) in a solution. Calculated as pH= log[H+]. The pH scale goes from 0 to 14.
pH <7 acidic
pH= 7 neutral
pH> 7 basic
A neutral solution has a pH of 7.Concentration of H+ and OH- are equal to each other. pH less than 7 are acidic and have greater concentration of hydrogen ions H+than hydroxide ions OH-. Solutions with a greater pH than 7 are basic and have a greater concentration of hydroxide ions (OH-) than hydrogen ions (H+). Adding a base will raise the pH and adding an acid will lower the pH. Human blood has a pH close to neutral (pH =7.4). The pH of blood is maintained by the use of buffers.
Buffers
Most solutions will rapidly become more acidic(lower pH) upon addition of acid or more basic upon addition of base. A buffer can help resist the change of pH by neutralizing the added acid or base. Cells function in a narrow pH range. The human body uses chemicals called buffers to regulate blood pH. Buffers can absorb excess H+ or OH-. A buffer is a solution of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffers maintain the proper pH of the body. The pH of human blood is maintained by a buffer system of CARBONIC ACID and BICARBONATE. One of the products of cellular metabolism is carbon dioxide. This CO2 reacts with water, forming CARBONIC ACID (H2CO3).
CO2 +H2O <> H2CO3.
Carbonic acid then dissociates forming H+ and bicarbonate ions (HCO3-).
H2CO3 <> H+ + HCO3- This buffer system works by H2CO3 (the weak acid) acting as a H+ donor in the presence of a base. Bicarbonate (the conjugate base) acts as a proton acceptor neutralizing any added acid.
Buffer equation
H2CO3<> H+ +HCO3- The dissociation reaction of carbonic acid forming H+ and HCO3 is reversible. If a base is added the reaction will run right to left, providing H+ to neutralize the base. However, the addition of acid will cause the reaction to run in reverse and the acid will be neutralized. The concentration of H+ in the system is maintained constant due to the equilibrium of the reaction, thus the pH of the solution is also maintained constant. The cytoplasm of cells is also buffered by a similar system using phosphate (PO4-) system.
Neutralization Reactions
Upon mixing an acid with a base, the H+ from the acid combines with the OH- from the base, forming water. The formation of water from hydrgoen ions and hydroxide ions is the heart of a neutralization reaction. Example, reaction occurs with NaOH is mixed with HCl. HCl + NaOH > H2O + NaCl.
Neutralization equation
The products of this acid-base neutralization reaction are water and sodium chloride ( a salt or ionic compound). Acid-base reactions typically form water and some type of ionic compound. When equal moles of acid and base are used, the system becomes neutral, with a pH of 7.
