Historically, the first chemical definition of an acid and a base was put forward by Svante Arrhenius, a Swedish chemist, in 1884. An Arrhenius acidA compound that increases the hydrogen ion concentration in aqueous solution. is a compound that increases the H+ ion concentration in aqueous solution. The H+ ion is just a bare proton, and it is rather clear that bare protons are not floating around in an aqueous solution. Instead, chemistry has defined the hydronium ionThe actual chemical species that represents a hydrogen ion. (H3O+) as the actual chemical species that represents an H+ ion. H+ ions and H3O+ ions are often considered interchangeable when writing chemical equations (although a properly balanced chemical equation should also include the additional H2O). Classic Arrhenius acids can be considered ionic compounds in which H+ is the cation. Table 12.1 "Some Arrhenius Acids" lists some Arrhenius acids and their names.
Table 12.1 Some Arrhenius Acids
Formula | Name |
---|---|
HC2H3O2 (also written CH3COOH) | acetic acid |
HClO3 | chloric acid |
HCl | hydrochloric acid |
HBr | hydrobromic acid |
HI | hydriodic acid |
HF | hydrofluoric acid |
HNO3 | nitric acid |
H2C2O4 | oxalic acid |
HClO4 | perchloric acid |
H3PO4 | phosphoric acid |
H2SO4 | sulfuric acid |
H2SO3 | sulfurous acid |
An Arrhenius baseA compound that increases the hydroxide ion concentration in aqueous solution. is a compound that increases the OH− ion concentration in aqueous solution. Ionic compounds of the OH− ion are classic Arrhenius bases.
Identify each compound as an Arrhenius acid, an Arrhenius base, or neither.
Solution
Test Yourself
Identify each compound as an Arrhenius acid, an Arrhenius base, or neither.
Answer
Acids have some properties in common. They turn litmus, a plant extract, red. They react with some metals to give off H2 gas. They react with carbonate and hydrogen carbonate salts to give off CO2 gas. Acids that are ingested typically have a sour, sharp taste. (The name acid comes from the Latin word acidus, meaning “sour.”) Bases also have some properties in common. They are slippery to the touch, turn litmus blue, and have a bitter flavor if ingested.
Acids and bases have another property: they react with each other to make water and an ionic compound called a salt. A saltAny ionic compound that is formed from a reaction between an acid and a base., in chemistry, is any ionic compound made by combining an acid with a base. A reaction between an acid and a base is called a neutralization reactionThe reaction of an acid and a base to produce water and a salt. and can be represented as follows:
acid + base → H2O + saltThe stoichiometry of the balanced chemical equation depends on the number of H+ ions in the acid and the number of OH− ions in the base.
Write the balanced chemical equation for the neutralization reaction between H2SO4 and KOH. What is the name of the salt that is formed?
Solution
The general reaction is as follows:
H2SO4 + KOH → H2O + saltBecause the acid has two H+ ions in its formula, we need two OH− ions to react with it, making two H2O molecules as product. The remaining ions, K+ and SO42−, make the salt potassium sulfate (K2SO4). The balanced chemical reaction is as follows:
H2SO4 + 2KOH → 2H2O + K2SO4Test Yourself
Write the balanced chemical equation for the neutralization reaction between HCl and Mg(OH)2. What is the name of the salt that is formed?
Answer
2HCl + Mg(OH)2 → 2H2O + MgCl2; magnesium chloride
Define Arrhenius acid.
Define Arrhenius base.
What are some general properties of Arrhenius acids?
What are some general properties of Arrhenius bases?
Identify each substance as an Arrhenius acid, an Arrhenius base, or neither.
Identify each substance as an Arrhenius acid, an Arrhenius base, or neither.
Write the balanced chemical equation for the neutralization reaction between KOH and H2C2O4. What is the salt?
Write the balanced chemical equation for the neutralization reaction between Sr(OH)2 and H3PO4. What is the salt?
Write the balanced chemical equation for the neutralization reaction between HCl and Fe(OH)3. What is the salt?
Write the balanced chemical equation for the neutralization reaction between H2SO4 and Cr(OH)3. What is the salt?
CaCl2 would be the product of the reaction of what acid and what base?
Zn(NO3)2 would be product of the reaction of what acid and what base?
BaSO4 would be product of the reaction of what acid and what base?
Na3PO4 would be product of the reaction of what acid and what base?
a compound that increases the H+ concentration in water
sour taste, react with metals, and turn litmus red
2KOH + H2C2O4 → 2H2O + K2C2O4; K2C2O4
3HCl + Fe(OH)3 → 3H2O + FeCl3; FeCl3
HCl and Ca(OH)2
H2SO4 and Ba(OH)2