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Below are some examples:

  1. HCl ( g ) + NH 3 ( g ) NH 4 + + Cl - In order to decide which substance is a proton donor and which is a proton acceptor, we need to look at what happens to each reactant. The reaction can be broken down as follows: HCl Cl - + H + and NH 3 + H + NH 4 + From these reactions, it is clear that HCl is a proton donor and is therefore an acid , and that NH 3 is a proton acceptor and is therefore a base .
  2. CH 3 COOH + H 2 O H 3 O + + CH 3 COO - The reaction can be broken down as follows: CH 3 COOH CH 3 COO - + H + and H 2 O + H + H 3 O + In this reaction, CH 3 COOH (acetic acid) is a proton donor and is therefore the acid . In this case, water acts as a base because it accepts a proton to form H 3 O + .
  3. NH 3 + H 2 O NH 4 + + OH - The reaction can be broken down as follows: H 2 O OH - + H + and NH 3 + H + NH 4 + In this reaction, water donates a proton and is therefore an acid in this reaction. Ammonia accepts the proton and is therefore the base . Notice that in the previous equation, water acted as a base and that in this equation it acts as an acid. Water can act as both an acid and a base depending on the reaction. This is also true of other substances. These substances are called ampholytes and are said to be amphoteric .

An amphoteric substance is one that can react as either an acid or base. Examples of amphoteric substances include water, zinc oxide and beryllium hydroxide.

Conjugate acid-base pairs

Look at the reaction between hydrochloric acid and ammonia to form ammonium and chloride ions:

HCl + NH 3 NH 4 + + Cl -

Looking firstly at the forward reaction (i.e. the reaction that proceeds from left to right ), the changes that take place can be shown as follows:

HCl Cl - + H + and

NH 3 + H + NH 4 +

Looking at the reverse reaction (i.e. the reaction that proceeds from right to left ), the changes that take place are as follows:

NH 4 + NH 3 + H + and

Cl - + H + HCl

In the forward reaction , HCl is a proton donor (acid) and NH 3 is a proton acceptor (base). In the reverse reaction , the chloride ion is the proton acceptor (base) and NH 4 + is the proton donor (acid). A conjugate acid-base pair is two compounds in a reaction that change into each other through the loss or gain of a proton. The conjugate acid-base pairs for the above reaction are shown below.

The reaction between ammonia and water can also be used as an example:

Conjugate acid-base pair

The term refers to two compounds that transform into each other by the gain or loss of a proton.

Khan academy video on acids and bases

Acids and bases

  1. In the following reactions, identify (1) the acid and the base in the reactants and (2) the salt in the product.
    1. H 2 SO 4 + Ca ( OH ) 2 CaSO 4 + 2 H 2 O
    2. CuO + H 2 SO 4 CuSO 4 + H 2 O
    3. H 2 O + C 6 H 5 OH H 3 O + + C 6 H 5 O -
    4. HBr + C 5 H 5 N ( C 5 H 5 NH + ) Br -
  2. In each of the following reactions, label the conjugate acid-base pairs.
    1. H 2 SO 4 + H 2 O H 3 O + + HSO 4 -
    2. NH 4 + + F - HF + NH 3
    3. H 2 O + CH 3 COO - CH 3 COOH + OH -
    4. H 2 SO 4 + Cl - HCl + HSO 4 -

Acid-base reactions

When an acid and a base react, they neutralise each other to form a salt . If the base contains hydroxide (OH - ) ions, then water will also be formed. The word salt is a general term which applies to the products of all acid-base reactions. A salt is a product that is made up of the cation from a base and the anion from an acid. When an acid reacts with a base, they neutralise each other. In other words, the acid becomes less acidic and the base becomes less basic. Look at the following examples:

Questions & Answers

what is the parallel circuit
Philani Reply
how many moles of H2O can be formed if 12,5 moi CH4 reacts with sufficient NH3 and O2
Nomcebo Reply
what atoms form covalent bond
hehe Reply
what is a mole
Thandeka Reply
a mole is a measure of large quantities of small entities such as atoms, molecules etc
what does STP stand for?
STP stands for Standard Temperature and Pressure.
A car drives straight off the edge of a cliff that is 54m high. The police at the scene of the accident observed that the point of the impact is 130m from the base of the clif. Calculate the initial velocity of the car when it went ovet the clif.
hanyani Reply
wat happens to current if resistors are in parallel connection
Mosima Reply
more current flows from the source that would flow for any of them individually,so the total total resistance is lower
what are the isotopes
Tlotlisang Reply
are different types of the same elemant but with different mass or atomic no.
i sotopes are different type of element with same atomic number but different mass number
yes i forgot some details😁
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why don't we insert the negative sign for 5 × 10 - 9 when substituting
Mpho Reply
Why does an enclosed gas exert pressure on the walls of a container
Palesa Reply
State the gay lussacs law
Anna Reply
what is the coefficient of Na in order to balanced the equation?_Na + MgCl2=2NaCl+Mg?
Arcel Reply
the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with.
Dealon Reply
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what are orbitals
Sphe Reply
examples of atoms whose Valence energy levels are not full and more to bond and become more stable
What is a valency
what is vacuum
Njabulo Reply
Vacuum, space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal).
evidence of reaction
Jason Reply

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Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
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