Acids are known for their ability to donate a proton, or hydrogen ion (\(H^+\)), when dissolved in water. This behavior, defined by increasing the concentration of hydrogen ions, gives acids their characteristic sour taste and corrosive properties, making substances like lemon juice or stomach acid so reactive.
Defining Bases and Alkalinity
The chemical opposite of an acid is a substance known as a base. Bases are defined by their ability to either release hydroxide ions (\(OH^-\)) into an aqueous solution or to accept a proton (\(H^+\)) from another substance. Bases often have a distinct set of physical properties, including a bitter taste and a slippery, soapy feel to the touch.
The terms “base” and “alkali” are often used interchangeably, but they have a distinct difference. An alkali is simply a base that is soluble, meaning it can dissolve in water. Therefore, all alkalis are bases, but not all bases are alkalis; for example, copper oxide is a base but does not dissolve in water, so it is not considered an alkali. Common examples of alkalis include sodium hydroxide and potassium hydroxide, which readily dissolve and release hydroxide ions to increase alkalinity.
The pH Spectrum
The strength of acids and bases is quantified using the pH scale. The “pH” value is a measure of the concentration of hydrogen ions (\(H^+\)) in a solution. This scale typically ranges from 0 to 14, where a pH less than 7 indicates an acidic solution and a pH greater than 7 indicates a basic, or alkaline, solution.
A pH of exactly 7 represents a neutral solution, such as pure water at room temperature. The scale is logarithmic, meaning that each whole number change represents a tenfold difference in hydrogen ion concentration. For instance, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5, and one hundred times more acidic than a pH of 6.
Neutrality and Chemical Reactions
When an acid and a base are mixed together, they react in a process known as neutralization. This reaction occurs where the acid’s hydrogen ions combine with the base’s hydroxide ions. The chemical result of this interaction is the formation of water (\(H_2O\)) and a compound called a salt. The final solution achieves neutrality, or a pH of 7, when a strong acid and a strong base are mixed in perfectly equal amounts.
The practical application is seen in medical remedies. For example, antacids, which are mild bases, are taken to neutralize the excess hydrochloric acid in the stomach that causes indigestion. The base in the antacid reacts with the stomach acid to produce a salt and water, thereby reducing the acidity and alleviating the discomfort.
Common Examples and Everyday Relevance
Bases are used in household cleaning and biological processes. Common examples of household bases include baking soda (sodium bicarbonate), which is used in cooking and as a mild antacid, and ammonia, often found in glass cleaners. Stronger bases like sodium hydroxide are used in drain cleaners and for manufacturing soap.
The body also relies heavily on a precise acid-base balance to function correctly. Human blood, for example, is slightly basic, maintaining a very narrow pH range, typically between 7.35 and 7.45. This tight regulation is necessary because small shifts in pH can disrupt biological processes, and the body uses bases, such as bicarbonate ions, to keep the blood within this range. Mild bases are also found in toothpaste to neutralize the acids produced by bacteria in the mouth, which helps prevent tooth decay.