The Basics of Arrhenius Bases

Tish Mancini, Nissa Garcia
  • Author
    Tish Mancini

    Tish Mancini has professional experience as a scientist, journalist, and educator. A graduate of the Pennsylvania State University with a Bachelor of Science in Food Science, she has spent the last 17 years in the classroom as a certified teacher of chemistry and biology in Florida.

  • Instructor
    Nissa Garcia

    Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

Learn to define Arrhenius Base. Understand the theory behind the behavior of bases, characteristics and limitations of Arrhenius bases, and see examples. Updated: 02/16/2022

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Arrhenius Base Definition

Since the time of the ancient Greeks, humans have attempted to classify substances, often according to their taste: sweet, sour, salty and bitter. The Romans refined this concept, calling sour-tasting substances like vinegar and lemon juice "acere," from which the modern word acid is derived. Defining a base was more elusive, but most societies understood the practical application of making a base, soap, from the reaction of ash and fat. The term synonymous with base, alkali, is an Arabic word describing the process.

Science continued to progress, adding to the understanding of acid-base chemistry with the discovery of litmus paper, and centuries later, neutralization reactions. The term "base" entered into use when describing substances that reacted with acids to produce salts. In 1884, Svante Arrhenius, a Swedish chemist and physicist published a paper on electrolytic solutions, discussing the hydrogen theory of acids. Among his conclusions were simple definitions of acids and bases. He stated that acids increased the concentration of hydrogen ions in aqueous (water-based) solutions, while bases increased hydroxide ion concentration. Decades later, the work was awarded a Nobel Prize, although it did not garner acclaim at the time it was published.

Modern chemistry recognizes three acid-base theories: Arrhenius, Bronsted-Lowry, and Lewis. Of the three, Arrhenius' theory is perhaps the easiest to understand, however it is the most limited definition, while the Lewis theory has the broadest definition.

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Svante Arrhenius earned a Nobel Prize for his work resulting in acid-base theory.

Arrhenius

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  • 0:00 What Is an Arrhenius Base?
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Arrhenius Base Examples

All Arrhenius bases will have the same basic pattern to its compound formula- a cation of various charge, and one or more hydroxides (OH^-) to balance the charge of the metal. The charge of hydroxide is 1^-. The formula of the ionic compound is expressed as a ratio. Metal cations located in Group 1 on the periodic table combine with the hydroxide ion in a 1:1 ratio, producing one hydroxide ion for each metal ion that dissociates in solution. All Group 1 metal hydroxides are soluble in water, and by definition would produce an Arrhenius base in solution.

  • NaOH_{(s)}\rightarrow Na^+_{(aq)} + OH^-_{(aq)}

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Sodium hydroxide dissociates to form Na+ and OH- in water.

NaOH dissociating

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  • LiOH_{(s)}\rightarrow Li^+_{(aq)} + OH^-_{(aq)}

Metal cations from Group 2 combine with the hydroxide ion dissociate in a 1:2 ratio, due to the metal ion's charge of 2+. Group 2 metal hydroxides vary in solubility, with some ions completely dissociating, and other ions dissociating to such a small degree that they are considered insoluble.

  • Ca(OH)_2 _{(s)} \rightarrow Ca^2+_{(aq)} + 2 OH^-_{(aq)}
  • Sr(OH)_2_{(s)} \rightarrow Sr^2+_{(aq)} + 2 OH^-_{(aq)}

How to identify an Arrhenius Base

An Arrhenius base can be identified by its physical and chemical properties. It will:

  • Have a pH greater than 7.

The pH scale ranges from 0-14 and is calculated from the negative logarithm of the hydrogen (or hydronium, H_3O^+) ion concentration. Above pH 7, the concentration of hydroxide ions is greater than hydronium ions, and the substance is basic. Note that chemicals with pH values at the either end of the scale are highly corrosive.

  • Have a bitter taste and slippery feel. Although most inorganic bases are not fit for human consumption, substances like soap, which has a pH of 9-10, does exhibit these properties.
  • Be able to neutralize an acid.

When an Arrhenius acid reacts with an Arrhenius base, the products are a salt and water. Consider this typical neutralization reaction:

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Frequently Asked Questions

How do you identify an Arrhenius base?

Arrhenius bases can be identified by its pH of 7 or higher, and its ability to react to neutralize an acid by producing a salt and water.

What is a Arrhenius base example?

Metal ions combined with hydroxide are classified as Arrhenius bases. Examples are NaOH (sodium hyroxide) and Ba(OH)2 (barium hydroxide). The polyatomic ion ammonium combined with hydroxide (NH4OH) is also an Arrhenius base.

What is a base according to Arrhenius?

According to Arrhenius, a base is a compound that increases concentration of hydroxide ions in a water-based solution, compared to an Arrhenius acid, which increases concentration of hydrogen ions in a water-based solution.

What does Arrhenius theory not explain?

The Arrhenius theory does not allow for bases such as ammonia (NH3) and sodium bicarbonate (Na2CO3), that do not produce hydroxide ions in solution.

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