Bases
Just as with acids, there are three definitions of a base.
Bases: The Definitions
According to the Arrhenius definition, a base produces OH- when in aqueous solutions. An example is sodium hydroxide (NaOH).
When you add NaOH to water, NaOH dissociates:
NaOH (aq)---> Na+(aq) + OH-(aq)
As you can see, NaOH dissociates and produces OH-, which is how Arrhenius defined a base.
Under Bronsted-Lowry, bases are as substances that accept H+ (protons). Ammonia (NH3) provides a good example of this definition:
NH3 (aq) + H2O(l) ---> (NH4)+ (aq) + OH- (aq)
In this reaction, ammonia (NH3) abstracted (took) a proton from water to form ammonium (NH4 +) and hydroxide (OH-). Thus, ammonia accepted a proton and is a base under the Bronsted-Lowry. We can also see that ammonia produced OH- and would therefore qualify as a base under the Arrhenius definition as well.
The Lewis definition says that bases are electron pair donors. By this definition, a given base must have at least one lone pair of electrons. Using the ammonia example again, ammonia is donating the electron pair on nitrogen to a hydrogen atom on water in order to form ammonia. The following figure may help you picture this. The red arrows indicate the movement of a pair of electrons.
Another example of ammonia as a Lewis base:
Here, ammonia is donating an electron pair to the electron-deficient boron in boron trichloride, which accepts a pair of electrons (making it a Lewis acid!).
For more resources, check out the following links:
On all of the definitions: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Acid
Specifically for the Arrhenius definition: https://www.intechopen.com/books/corrosion/the-arrhenius-acid-and-base-theory
For Bronsted-Lowry: https://courses.lumenlearning.com/suny-mcc-introductorychemistry/chapter/bronsted-lowry-acids-and-bases/
On Lewis bases: https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/lewis.php
Other Properties of Bases
Bases have pH>7 (by definition) or pH>8 (commonly).
Bases are also known as "alkali"
IF tasted, based would be "bitter" (though I strong advise against tasting a base!!)
Bases also feel slippery to the touch. Just think of how soap feels when you use it!
Examples of bases
Bases can be found in substances such as:
sea water
baking soda
milk of magnesia( Mg(OH)2)
ammonia solution
soap water
bleach
anti-acids
drain cleaner,
toothpaste
laundry detergent/washing powder
quick lime
Chemical formulas of bases include:
Strong Bases:
NaOH (sodium hydroxide)
LiOH (lithium hydroxide)
Ba(OH)2 (barium hydroxide)
KOH (potassium hydroxide)
Sr(OH)2 (strontium hydroxide)
Ca(OH)2 (calcium hydroxide)
Weak bases:
NH3 (ammonia)
anions (of strong acids) like Cl- (chloride), F- (fluoride), NO3- (nitrate), C2H3O2 - (acetate)
CO3 2- (carbonate ion)
CH3NH2 (methylamine)
C5H5N (pyridine)
HCO3 - (bicarbonate/hydrogen carbonate)
C6H5NH2 (aniline)