why was the concept of PH solution widely accepted in relation to the concentration of h + ions per litre of the solutions
Answers
Expressing the acidity of a solution by using the molarity of the hydrogen ion is cumbersome because the quantities are generally very small. Danish scientist Søren Sørensen (1868 - 1939) proposed an easier system for indicating the concentration of H+ called the pH scale. The letters pH stand for the power of the hydrogen ion. The pH of a solution is the negative logarithm of the hydrogen-ion concentration.
pH=−log[H+](8.6.5)
In pure water or a neutral solution [H+]=1.0×10−7M . Substituting this value into the pH expression:
pH=−log[1.0×10−7]=−(−7.00)=7.00(8.6.6)
The pH of pure water or any neutral solution is thus 7.00. Due to the somewhat less intuitive rules for dealing with significant figures in the context of logarithms, only the numbers ot the right of the decimal point in the pH value are the significant figures. Since 1.0×10−7 has two significant figures, the pH can be reported as 7.00.
A logarithmic scale condenses the range of acidity to numbers that are easy to use. For example, a solution in which [H+]=1.0×10−4M has a hydrogen-ion concentration that is 1000 times higher than in pure water. The pH of such a solution is 4.00, a difference of 3 pH units. Notice that when [H+] is written in scientific notation and the coefficient is 1, the pH is simply the exponent with the sign changed. The pH of a solution in which [H+]=1.0×10−2M is 2.0 and the pH of a solution in which [H+]=1.0×10−10M is 10.0. If the coefficient is not equal to 1, a calculator must be used to find the pH. For example, the pH of a solution in which [H+]=2.3×10−5M can be found as shown below.
pH=−log[2.3×10−5]=4.64(8.6.7)
As we saw earlier, a solution in which [H+] is higher than 1×10−7M acidic, while a solution in which [H+] is lower than 1.0×10−7M is basic. Consequently, solutions with pH values of less than 7 are acidic, while solutions with pH values higher than 7 are basic. The figure below illustrates this relationship, along with some examples of the pH for various solutions.