ACIDS AND BASES AND THEIR REACTIONS

ACID/BASE THEORY ARRHENIUS Svante August Arrhenius (February 19, 1859 – October 2, 1927) a Swedish chemist and one of the founders of the science of physical chemistry. The Arrhenius equation and the Lunar Crater Arrhenius are named after him.

According to Arrhenius, an acid is: HA ---> H+ + A¯ any substance which delivers hydrogen ion (H+) to the solution. This would be a generic base: XOH ---> X+ + OH¯ any substance which delivers hydroxide ion (OH¯) to the solution.

When acids and bases react according to this theory, they neutralize each other, forming water and a salt: HA + XOH  H2O + XA Keeping in mind that the acid, the base and the salt all ionize, we can write this: H+ + A¯ + X+ + OH¯  H2O + X+ + A¯ H+ + OH¯  H2O

ACID BASE THEORY BRONSTED-LOWRY Johannes Bronsted was a Danish physical chemist known for a widely applicable acid-base concept identical to that of Thomas Martin Lowry of England. Though both men introduced their definitions simultaneously (1923), they did so independently of each other.

An acid is a substance from which a proton can be removed. HCl + H2O <===> H3O+ + Cl¯ HNO3 + H2O <===> H3O+ + NO3¯ Remember: proton, hydrogen ion and H+ all mean the same thing

A base is a substance that can remove a proton from a substance. NH3 + H2O <===> NH4+ + OH¯ Very common in the chemistry world is this definition set: An acid is a "proton donor." A base is a "proton acceptor."

PROPERTIES OF ACIDS Acids release a hydrogen ion into water (aqueous) solution. Acids neutralize bases in a neutralization reaction. An acid and a base combine to make a  salt and water. A salt is any ionic compound that could be made with the anion of an acid and the cation of a base. The hydrogen ion of the acid and the hydroxide ion of the base unite to form water. Acids corrode active metals. When an acid reacts with a metal, it produces a compound with the cation of the metal and the anion of the acid and hydrogen gas.

Acids turn blue litmus to red Acids turn blue litmus to red. Litmus is one of a large number of organic compounds that change colors when a solution changes acidity at a particular point. Litmus is the oldest known pH indicator. It is red in acid and blue in base. Litmus does not change color exactly at the neutral point between acid and base, but very close to it. Acids taste sour. The word 'sauer' in German means acid and is pronounced almost exactly the same way as 'sour' in English. (Sauerkraut is sour cabbage, cabbage preserved in its own fermented lactic acid.

PROPERTIES OF BASES Bases release a hydroxide ion into water solution. Bases neutralize acids in a neutralization reaction. The word reaction is: Acid plus base makes water plus a salt. HY + XOH HOH + XY Bases denature protein. This accounts for the "slippery" feeling on hands when exposed to base. Strong bases that dissolve in water well, such as sodium or potassium lye are very dangerous because a great amount of the structural material of human beings is made of protein.

Bases turn red litmus to blue Bases turn red litmus to blue. This is not to say that litmus is the only acid- base indicator, but that it is likely the oldest one. Bases taste bitter. There are very few food materials that are alkaline, but those that are taste bitter. It is even more important that care be taken in tasting bases. Tasting of bases is more dangerous than tasting acids due to the property of stronger bases to denature protein.

STRONG ACIDS The common acids that are almost one hundred percent ionized are: HNO3 - nitric acid HCl - hydrochloric acid H2SO4 - sulfuric acid HClO4 - perchloric acid HBr - hydrobromic acid HI - hydroiodic acid The acids on this short list are called strong acids, because the amount of acid quality of a solution depends upon the concentration of ionized hydrogens.

STRONG BASES Likewise, there is a short list of strong bases, ones that completely ionize into hydroxide ions and a conjugate acid. All of the bases of Group I and Group II  metals except for beryllium are strong bases. LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide RbOH - rubidium hydroxide CsOH - cesium hydroxide Mg(OH)2 - magnesium hydroxide Ca(OH)2 - calcium hydroxide Sr(OH)2 - strontium hydroxide Ba(OH)2 - barium hydroxide

pH Scale pH is a measure of the acidity or alkalinity of a solution. Solutions with a pH less than seven are considered acidic Those with a pH greater than seven are considered basic (alkaline). pH 7 is considered neutral because it is the accepted pH of pure water at 25 °C

Reactions involving acids and bases are quite common and represent an extremely important area of chemistry, encompassing industrial and biological processes. We commonly encounter acids and bases in our every day life as can be seen by these household items. Most Acid-Base reactions are carried out in water.