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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

pauli's exclusion is based on what?
avdhesh Reply
What is greatest modification made in dalton's atomic theory?
Ngwesse Reply
Types of electrolytes
Treasure Reply
Strong, weak and non-electrolytes
Grace
welcome
Alieu
thanks what's this platform all about
Nnamdi
list 6 subatomic particles and their mass, speed and charges
Dubem Reply
combination of acid and base
Ayibiro Reply
that salt
Talhatu
calculate the mass in gram of NaOH present in 250cm3 of 0.1mol/dm3 of its solution
Omego Reply
The mass is 1.0grams. First you multiply the molecular weight and molarity which is 39.997g/mol x 0.1mol/dm3= 3.9997g/dm3. Then you convert dm3 to cm3. 1dm3 =1000cm3. In this case you would divide 3.9997 by 1000 which would give you 3.9997*10^-3 g/cm3. To get the mass you multiply 3.9997*10^-3 and
Kokana
250cm3 and get the mass as .999925, with significant figures the answer is 1.0 grams
Kokana
nitrogen, phosphorus, arsenic, antimony and Bismuth
faith Reply
What is d electronic configuration of for group 5
Miracle Reply
Can I know d electronic configuration of for group 5 elements
Miracle
2:5, 2:8:5, 2:8:8:5,...
Maxime
Thanks
Miracle
Pls what are d names of elements found in group 5
Miracle
define define. define
Muh Reply
what is enthalpy
Ayilaran Reply
total heat contents of the system is called enthalpy, it is state function.
Sajid
background of chemistry
Banji Reply
what is the hybridisation of carbon in formic acid?
Maham Reply
sp2 hybridization
Johnson
what is the first element
Josh Reply
HYDROGEN
Liklai
Element that has positive charge and its non metal Name the element
Liklai
helium
oga
sulphur
oga
hydrogen
Banji
account for the properties of organic compounds
mercy Reply
properties of organic compounds
mercy
what's the difference between molecules and compounds
Amha Reply
A compound can be a molecule however compounds must contain more than one element. For example ozone, O3 is a molecule but not a compound.
Justin
what is che? nd what is mistry?
Mukhtar

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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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