What do you mean by pH value?

Solution

Sorensen in 1909 suggested a convenient method of expressing hydronium ion concentration known as pH scale. The pH of a solution may be defined as the numerical value of the negative power of which 10 must be raised in order to express hydronium ion concentration i.e.

open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space 10 to the power of negative pH end exponent

Taking logarithm on both the sides,

log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space minus pH space log space 10

pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets

Thus pH of a solution may also be defined as the negative logarithm of hydronium ion concentration.
Also,

pH space equals space log space fraction numerator 1 over denominator open square brackets straight H subscript 3 straight O to the power of plus close square brackets end fraction

Hence pH of a solution is defined as the logarithm of the reciprocal of hydronium ion concentration.

left parenthesis straight i right parenthesis space For space pure space water space and space for space other space neutral space solution colon space space space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space equals space 1 space cross times space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent therefore space space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets space space space space space space space space space space space space equals negative log space left parenthesis 1 space cross times space 10 to the power of negative 7 end exponent right parenthesis space equals space minus left parenthesis negative 7 right parenthesis space log space 10 space space space space space space space space space space space space space equals space plus 7 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left square bracket because space log space 10 space equals space 1 right square bracket

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As pH of a solution goes on decreasing below 7, the acidic nature of solution goes on increasing.
If pH lies between:
(a) 0 and 2, the solution is strongly acidic,
(b) 2 and 4, the solution is moderately acidic,
(c) 4 and 7, the solution is weakly acidic.
(iii) In basic solution:
$open square brackets straight H subscript 3 straight O close square brackets to the power of plus space less than space 1 space cross times space 10 to the power of negative 7 end exponent space mol space straight L to the power of negative 1 end exponent space such space as space 10 to the power of negative 8 end exponent comma space 10 to the power of negative 9 end exponent comma space 10 to the power of negative 10 end exponent space mol space straight L to the power of negative 1 end exponent$
$We space know comma space space space pH space equals space minus log space open square brackets straight H subscript 3 straight O to the power of plus close square brackets therefore space space space space space space pH thin space greater than 7 space such space as space 8 comma space 9 comma space 10 space etc.$

As pH of a solution goes on increasing above 7, the basic nature of the solution goes on increasing.

If pH lies between:
(a) 7 and 10, the solution is weakly basic,
(b) 10 and 12, the solution is moderately basic,
(c) 12 and 14, the solution is strongly basic.

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Equilibrium

What do you mean by pH value?

Some More Questions From Equilibrium Chapter

A crystal of common salt of a given mass is kept in its aqueous solution. After 24 hours, its mass remains the same. Is the crystal in equilibrium with the solution?

What is the role of forward and backward reactions at equilibrium of a reversible reaction?

What is a forward reaction?

What condition favours a reversible reaction?

What is a backward reaction?

What type of equilibrium is attained in a reversibe chemical change?

What is meant by a system at dynamic equilibrium?

discuss the effect of a catalyst on equilibrium ?

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