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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 .
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 does Redox reactins mean?
kholeka Reply
Reaction in which there is transfer of electrons between elements
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state Faraday's law in word
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which rules do you have to follow to identify oxidation numbers
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Why do vectors have arrows?
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vector quantity has both direction and magnitude so arrows illustrate the direction of the vector
Mhleli
how to calculate net electric field at a point
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what are controlled variables
Link Reply
Independent variables in an experiment which influence the outcome results
Boss
Such as temperature when dealing with ohms law
Boss
variables whose amount is determined by the person doing the experiment
Clemencia
how to calculate exodation number
Cphiwe Reply
Calculate relative atomic mass
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what is chemical bonding?
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Chemical Bonding is a mutual attraction between two atoms resulting from the simultaneous attraction between their nuclei and the outer elections
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How would you go about finding the resistance of an unknown resistor using only power supply, a voltmeter and a known resistance
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who is the scientist who discovered electromagnetism
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what happens to the galvanometer when the switch is closed ?
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how do we identify an oxidising or reducing agent in a reaction?
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hey
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@zivele in your products the element with an oxidation number less than 0 is a reducing and the one with an oxidation number greater than 0 is oxidising
sessy
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Vihanga Reply
Formula for concentration
Kabelo Reply
c=m/MV
Zipho
if given number of moles and volume , can use c=n/V
sibahle
Chemistry term three topic is stressing me out, I really need a huge help
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during a snooker competition ,a 200g ball A m moving with velocity va collide head on with a identical ball B that was at rest.A after the collision ball A remains at rest wile ball B moves on with a velocity of 4m/s? With what speed was ball a moving before the collision
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a vector can be resolved into a horizontal component only
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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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