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By the end of this section, you will be able to:
  • Identify acids, bases, and conjugate acid-base pairs according to the Brønsted-Lowry definition
  • Write equations for acid and base ionization reactions
  • Use the ion-product constant for water to calculate hydronium and hydroxide ion concentrations
  • Describe the acid-base behavior of amphiprotic substances

Acids and bases have been known for a long time. When Robert Boyle characterized them in 1680, he noted that acids dissolve many substances, change the color of certain natural dyes (for example, they change litmus from blue to red), and lose these characteristic properties after coming into contact with alkalis (bases). In the eighteenth century, it was recognized that acids have a sour taste, react with limestone to liberate a gaseous substance (now known to be CO 2 ), and interact with alkalis to form neutral substances. In 1815, Humphry Davy contributed greatly to the development of the modern acid-base concept by demonstrating that hydrogen is the essential constituent of acids. Around that same time, Joseph Louis Gay-Lussac concluded that acids are substances that can neutralize bases and that these two classes of substances can be defined only in terms of each other. The significance of hydrogen was reemphasized in 1884 when Carl Axel Arrhenius defined an acid as a compound that dissolves in water to yield hydrogen cations (now recognized to be hydronium ions) and a base as a compound that dissolves in water to yield hydroxide anions.

In an earlier chapter on chemical reactions, we defined acids and bases as Arrhenius did: We identified an acid as a compound that dissolves in water to yield hydronium ions (H 3 O + ) and a base as a compound that dissolves in water to yield hydroxide ions (OH ). This definition is not wrong; it is simply limited.

Later, we extended the definition of an acid or a base using the more general definition proposed in 1923 by the Danish chemist Johannes Brønsted and the English chemist Thomas Lowry. Their definition centers on the proton, H + . A proton is what remains when a normal hydrogen atom, 1 1 H , loses an electron. A compound that donates a proton to another compound is called a Brønsted-Lowry acid    , and a compound that accepts a proton is called a Brønsted-Lowry base    . An acid-base reaction is the transfer of a proton from a proton donor (acid) to a proton acceptor (base). In a subsequent chapter of this text we will introduce the most general model of acid-base behavior introduced by the American chemist G. N. Lewis.

Acids may be compounds such as HCl or H 2 SO 4 , organic acids like acetic acid (CH 3 COOH) or ascorbic acid (vitamin C), or H 2 O. Anions (such as HSO 4 , H 2 PO 4 , HS , and HCO 3 ) and cations (such as H 3 O + , NH 4 + , and [ Al ( H 2 O ) 6 ] 3+ ) may also act as acids. Bases fall into the same three categories. Bases may be neutral molecules (such as H 2 O, NH 3 , and CH 3 NH 2 ), anions (such as OH , HS , HCO 3 , CO 3 2− , F , and PO 4 3− ) , or cations (such as [ Al(H 2 O) 5 OH ] 2+ ) . The most familiar bases are ionic compounds such as NaOH and Ca(OH) 2 , which contain the hydroxide ion, OH . The hydroxide ion in these compounds accepts a proton from acids to form water:

Questions & Answers

what is catenation
Oladuji Reply
The property of carbon to form long chain with other atom!
hydrocarbons can be classified as..1.Aliphatic compounds 2.cyclic compounds.under aliphatic compounds there are two types saturated hydrocarbons(alkanes) and unsaturated hydrocarbons(alkenes and alkynes).
Niroshan Reply
thanks but i have also heard of aromatic hydrocarbons
so am kinda confused
hello i have big problems in understanding organic chemistry
emmanuel Reply
what are the main types of hydrocarbon
how many elements are in the periodic table
emmanuel Reply
please what are the main types of hydrocarbons
why Rutherford uses the gold foil instead of other metals?
Lareb Reply
Rutherford chose gold was because its extremely malleable. One can stretch gold foil until it is only a few atoms thick in places, which is not possible with aluminum. If the foil were too thick, there would be no transmission of particles at all; the whole point was to demonstrate that most alpha
wjat does Rutherford mean?
Ernest Rutherford was the scientist that preformed the experiment.
although other metals are also present which are more melleable!?so
what is a balanced equation 4 trioxonitrate (V)acid and sodium hydroxide?
Marcel Reply
proved ur Worth: If A is a of trioxonitrate(V)acid,HNO3' of unknown concentration .B is a standard solution of sodium hydroxide containing 4.00g per dm cube of solution.25cm cube portions solution B required an average of 24.00cm cube of solution A for neutralization,using 2 drops of methyl orange.
calculate the concentration of solution B in moles per dm cube
calculate the concentration of solution A and B in moles per DM cube
finally calculate the concentration in g/dm cube of HNO3 in solution A (H=1,N=14,O=16,Na=23)
calculate the standard enthalpy of formation for propane(C3H8) from the following data; 1), C3H8+5O2->3CO2+4H2O; -222.0kJ/mol 2), C+O2->CO2;-395.5kJ/mol 3),H2+O->H2O; 285.8kJ/mol
let eventually of formation of propane = X X + (-222)=3×(-395.5)+4×(-286) rearrange to find X
wat is electrolysis?
Mgbachi Reply
it is the chemical decomposition of a substance when electric current is passed through it either in molten form or aqueous solution
list the side effect of chemical industries
Chelsea Reply
how do you ionise an atom
Rabeka Reply
many ways ,but one of them is when the atom becomes heated to a certain temperature the surface electron becomes too energetic and leaves the atom because the attraction between the nucleus and the electron becomes overpowered by the energetic eletron
also hitting of two atoms can cause transfer of surface electrons
and when this transfers occur the atom becomes ionised
who is doing Cape chemistry tomorrow?
caramel Reply
What is hybridization
edmondnti Reply
the mix between different breeds of species in one
it is the blending of orbitals.
the mixing of orbital
are covalent bonds influenced by factors such as temperature and pressure?
patrick Reply
what is catalyst used for mirror test
Sanjay Reply
when an atom looses electron, what does it become?
Abdullahi Reply
it's oxidized and called an ion
Now, I get it
can you give an example please, if you don't mind
a positive ion,become positively charged/a cation.
sodium plus one is simple cation is exmpl
Taking Sodium as example..... it carries a positive charge which means it is positively charged.....when it gains an electron, it is reduced cuz an electron is negatively charged.....also when an atom looses an electron, it becomes positively charged and when it gains, it becomes negatively charged.
typically, ionization is the process where an atom looses or gains electron(s) to form ion(s) either a positively or negatively
what is copper
Bryan Reply
just an element

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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