Ph of sample of rain water at 25degree cecius is 5 calculate the conc of h+
Answers
Answer:
A common means of expressing quantities, the values of which may span many orders of magnitude, is to use a logarithmic scale. One such scale that is very popular for chemical concentrations and equilibrium constants is based on the p-function, defined as shown where “X” is the quantity of interest and “log” is the base-10 logarithm:
pX = −log X
The pH of a solution is therefore defined as shown here, where [H3O+] is the molar concentration of hydronium ion in the solution:
pH = −log[H3O+]
Rearranging this equation to isolate the hydronium ion molarity yields the equivalent expression:
[H3O+] = 10−pH
Likewise, the hydroxide ion molarity may be expressed as a p-function, or pOH:
pOH = −log[OH−]
or
[OH−] = 10−pOH
Finally, the relation between these two ion concentration expressed as p-functions is easily derived from the Kw expression:
Kw = [H3O+][OH−]
−logKw = −log([H3O+][OH−]) = −log[H3O+] + −log[OH−]
pKw = pH + pOH
At 25 °C, the value of Kw is 1.0 × 10−14, and so:
14.00 = pH +pOH
As we learned earlier, the hydronium ion molarity in pure water (or any neutral solution) is 1.0 × 10−7 M at 25 °C. The pH and pOH of a neutral solution at this temperature are therefore:
pH = −log[H3O+] = −log(1.0 × 10−7) = 7.00
pOH = −log[OH−] = −log(1.0 × 10−7) = 7.00