ACKNOWLEDGEMENT:
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Figure
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Source of Figure
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Figure 1
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www.mysutro.com
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Acids:
Acids are defined as solvents that produce Hydrogen, H+,
ions as the only positive ions in their aqueous solutions, and whose pH is less
than 7 on the pH scale.
pH Scale:
pH is defined as the – log of H+ ions
concentration in an aqueous solution. The scale is a number line beginning from
0 and ending on 14. The pH of all acids ranges from 0 to 6, pH 7 is the pH of
neutral solutions, while the pH of bases ranges from 8 to 14. The smaller the
pH, the stronger the acid and the larger the pH the stronger the base.
Figure 1:
Calculating pH:
Acids:
pH = - log(H+ ions concentration in mol/dm3
or M)
Example 1: An aqueous solution of H2SO4
contains 1 x 10-3 M of H+ ions. Calculate its
pH.
pH = - log(H+ ions concentration in mol/dm3
or M)
pH = - log (1 x 10-3)
pH = 3
Bases:
p(OH) = - log(OH- ions concentration in mol/dm3
or M)
pH = 14 – p(OH)
Example 2: An aqueous solution of NaOH contains
1 x 10-2 M of OH- ions. Calculate its pH.
p(OH) = - log(OH- ions concentration in mol/dm3
or M)
p(OH) = - log(1 x 10-2)
p(OH) = 2
pH = 14 – p(OH)
pH = 14 – 2
pH = 12
Table 1: Indicators
and their colour change in acidic and basic medium
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Indicator
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Colour in Acids
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Colour in Bases
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pH at which colour changes
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Litmus paper
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Red
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Blue
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4.5 to 8.3
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Methyl Orange
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Red
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Yellow
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3.1 to 4.4
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Screened Methyl Orange
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Red
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Green
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3.2 to 4.5
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Universal Indicator
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Red
| Voilent |
7
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Phenolphthalein
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Colourless
| Pink |
8.3 to 10
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