Robert Boyle (1627-1691), an Irish chemist, was the first person to classify certain chemicals as either acids or bases. Boyle made his classifications based on their properties. However, he was unable to explain why acids and bases have the properties that exist in them. In another 200 years, a Swedish scientist came along to answer this question, namely Svante Arrhenius (1859-1927).
Arrhenius was the first scientist to explain that when a substance dissolves in water, it will break down into its ions. An ion is a charged particle that is formed when an atom gives up or takes on electrons. An atom is the smallest unit of an element that has the properties of the element. Atoms are considered the building blocks of matter.
Arrhenius Acids and Bases
Atoms are made up of three basic subatomic particles, one of which is an electron. The other two subatomic particles are protons and neutrons. Both protons and electrons carry an electrical charge. Protons are positively charged, while electrons are negatively charged. Protons are located in the nucleus or centre of an atom. Electrons move rapidly around the nucleus in a series of energy levels or shells. In a neutral atom, the number of protons inside the nucleus is equal to the number of electrons moving around it. Because the atom contains an equal number of positively charged protons and negatively charged electrons, its net charge is zero.
Arrhenius suggested that disassociation happens to bases too. But he believed that instead of releasing a positive hydrogen ion, as acids do, bases contributed a hydroxide ion to the solution. A hydroxide ion is a negative ion, and it is written OH. For example, if the base sodium hydroxide is dissolved in water, it will break up into sodium ions and hydroxide ions. So, Arrhenius defined an acid as any substance that releases hydrogen ions (H) when it is dissolved in water. He defined a base as any substance that releases hydroxide ions (OH–). This will explain the reason why all acids have similar properties; it is because they all release H+ ions. It also explains the similarities among bases. All bases, according to Arrhenius’ definition, release OH– ions. It also explains why water forms when acids and bases are mixed.
Determination of Molecular Weight
The molecular formula of a compound is the formula which shows the actual number of atoms in a molecule of the compound. The molecular formula may be the same as the empirical formula or a multiple of it. To determine the molecular formula of a molecular compound, the empirical formula and the molecular weight must be known. Since the molecular formula for a compound is either the same or a multiple of the empirical formula, the following relationship is helpful in determining the molecular formula.
Molecular weight = n (Empirical formula weight)
[or]
n = Molecular weight /Empirical formula weight
Then, multiplying the coefficients in the empirical formula by n gives the actual molecular formula.
