Acids/Bases - Theory


Explore the discoverer's biography, including general facts about his life and anecdotes regarding how he made this particular discovery. Also see other significant scientific discoveries built largely on this concept and other real-world applications in history that may not still be relevant.


Svante Arrhenius (1859-1927) was born in Vik, Sweden. He taught himself to read at age three and learned arithmetic at a young age from his father's accounting. Electrolytic conductivity was the subject of his dissertation, which was, in effect, given a grade of D by the professors reviewing it. However, this work was the basis of his Nobel Prize in Chemistry. Arrhenius became a professor at Stockholm University College. In 1884, he postulated the definition of acids and bases that has come to take his name. Five years later he proposed the idea of activation energy, that for a reaction to take place the molecules have to be given a certain amount of energy. Other topics on which Arrhenius did research included astronomy and the carbon dioxide level in Earth's atmosphere. Arrhenius was the first to theorize that carbon dioxide levels in the atmosphere could change the temperature by the greenhouse effect. However, he saw this completely as a beneficial phenomenon, because a warmer world would have higher plant yields according to him. Arrhenius was on the Nobel Physics Committee, where he advocated for people he liked to receive a Nobel Prize and his enemies to be denied one. Arrhenius himself won the Nobel Prize in Chemistry in 1903.


Concept Definition

Study the primary definition of this concept, broken into general, basic, and advanced English definitions. Also see the mathematical definition and any requisite background information, such as conditions or previous definitions.


An Arrhenius acid dissociates to form H3O+ (hydronium ions) when dissolved in water, while an Arrhenius base dissociates to form OH- (hydroxide ions) when dissolved in water.


An Arrhenius acid dissociates to form H3O+ (hydronium ions) when dissolved in water, while an Arrhenius base dissociates to form OH- (hydroxide ions) when dissolved in water. Many substances that are considered acids and bases are excluded when this definition is used to determine acids and bases.



Learn important vocabulary for this concept, including words that might appear in assessments (tests, quizzes, homework, etc.) that indicate the use of this concept.

 Important Vocabulary

Term Context
hydronium ion
  • Water dissociates into hydroxide and hydronium ions.
hydroxide ion
  • Water dissociates into hydroxide and hydronium ions.
  • Lemon juice has a pH of 2.


Classroom Demonstations

Investigate lab procedures suitable for live classroom demonstrations or guided student exploration.

Students requiring adaptations to gain the full benefit of a demonstration may find a worksheet with guided observations useful. Alternatively, a teacher may wish to use a worksheet with guided observations to model what observations all students should be making during a demonstration.

The Demonstration Observation Worksheet is available in

  • PDF [ready to print]
  • Word 2007/2008 DOCX [free to edit/adapt further]


Colorful Electrolysis -- Decomposition of Water


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Colorful Electrolysis -- Decomposition of Water

Colorful Electrolysis -- Decomposition of Water

Credit: Yan Luo

Author: Yan Luo
This colorful water electrolysis demonstration is a decomposition reaction of water molecules to produce hydrogen and oxygen gases. The mole ratio of hydrogen and oxygen atoms in water molecules is shown not to be 1:1. H+ is a temporary direct product of the reaction before they soon form nonpolar covalent bonds with each other as H2 gas. The temporary H+ is acidic in solution which changes the color of the bromothymol blue solution to yellow.Also because of the temporaryness, only the solution at the cathode instead of the entire dish changes color.
Demonstration for decomposition reactions. It can also be used to demonstrate electrolysis reactions and the use of indicators.
Futher Images
tn_colorful-electrolysi-6-p1-87.jpg tn_colorful-electrolysi-6-p2-87.jpg tn_colorful-electrolysi-6-p3-87.jpg tn_colorful-electrolysi-6-p4-87.jpg  
Credits, from left: Yan Luo, Yan Luo, Yan Luo, Yan Luo
Regular laboratory guidelines (eg. gloves, goggles, etc) should be followed.
A petri dish Two wires with alligator clips A petri dish A stir rod A 9V battery Two mechanical pencil leads
Bromothymol blue solution (with an eye dropper) A little (about 1 gram) table salt (or any highly soluable, neutral salt) Water (enough to fill 3/4 of the petri dish)
Preperation: Petri Dish Fill 3/4 of the petri dish with water. Put a little (about 1 gram) table salt (or any other highly soluable, neutral salt) into the petri dish. Dissolve the salt completely with water using a stir rod [to introduce ions into the solution to allow for a complete circuit]. Use an eye dropper to add 2-3 drops (amount may vary-depends on the color) of bromothymol blue solution into the petri dish until the blue color can easily be observed. Electric Circuit: Connect both wires each to a terminal of the battery with no other connection between the two wires [to prevent a short circuit]. Connect the other side of a wire to a mechanical pencil lead. Follow the same procedure to connect the other wire to another mechanical pencil lead. Make sure the two mechanical pencil leads are not directly connected [to prevent a short circuit]. Demonstration: Place both of the pencil leads into the petri dish without letting the pencil leads touching each other. What to observe: Does the solution change color? If so, what are the initial and final colors? Is there a specific location inside the petri dish around which the color changes? Does solution in the entire dish change color? What are some differences between the two ends in which a mechanical pencil lead is immersed in solution (in terms of color, amount of bubbles, etc)? What happens after the electric circuit setup is removed and the solution is allowed to sit for 5 minutes?
Bromothymol blue turns yellow in acdic solutions. When oxygen is produced as the gas product in the anode of the electrolysis reaction, the oxidation half reaction is shown as below: $text{2H}_2text{O}_{(l)} to text{O}_2_{(g)} + text{4H}^{+}_{(aq)} + text{4e}^{-}_{(aq)}$ The formation of H+ causes the color of bromothymol blue change to yellow. There is more gas produced on the cathode side than on the anode side, indicating that there are more moles of hydrogen atoms than oxygen atoms in water molecules (the mole ratio of hydrogen to oxygen in water molecules is not 1:1, but indeed 2:1). The formation of H+ is temporary, and after the electric circuit setup is removed and the solution is allowed to sit for 5 minutes, the color of the solution changes back to its original color [blue]. ______________________________________________________________________________________________________ Related videos can be view here: Animation Click for video Acidity Click for video Standard setup with gas testing Click for video Distilled water Click for video
The liquid waste can be disposed directly down the sink. The battery should be recycled or reused.
Difficulty:No specific experience required
Preparation Time:2 minutes Demonstration Time: 1 minutes
Availability of Materials:Local grocery store
Cost of materials:$2
Last Updated:Tue 09 Aug 2011 12:44:46 EDT Viewed:132748 times viewed, Darren Fix, August 11, 2009,

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