Show how to calculate the pH of pure water or a neutral solution.
Keq=1.8 x 10^-16 ====> determined experimentally and is accepted as the value at 25.0 C
Assuming 1L of water is 1000g and the molecular weight of water is 18.02g/mole.......
1000g/L*(mole/18.02g)=55.5 M
H2O ------------> H^+ + OH^-
Let X =H^+=OH^-
Keq=1.8 x 10^-16=[X][X]/[55.5M]
1.8 x 10^-16*[55.5M]= X^2
9.99 x 10^-15= 1 x 10^-14= X^2
√(1 x 10^-14)= X^2
1 x 10^-7=X
Back to the following relationship:
9.99 x 10^-15= 1 x 10^-14= X^2
1 x 10^-14= [H^+][OH^-]
-log[1 x 10^-14]=-log [H^+]*-log[OH^-]
14=pH+pOH
H2O ==> H^+ + OH^-
(H^+)(OH^-) = Kw = 1E-14
The equation tells you (H^+) = (OH^-)
(H^+)(H^+) = 1E-14 = (H^)^2
(H^+) = sqrt (1E-14) = 1E-7 M
pH = -log(H^+) = -log (1E-7) = 7
Since H^+ = OH^-, then pOH is 7 also and OH^- =1E-7 M
You will find pH + pOH = 14 helpful also.
To calculate the pH of pure water or a neutral solution, you need to know the concentration of hydrogen ions (H+). In pure water, the concentration of H+ ions is equal to the concentration of hydroxide ions (OH-).
The pH scale is a logarithmic scale that represents the acidity or basicity of a solution. It ranges from 0 to 14, where 7 is considered neutral. The lower the pH value, the more acidic the solution, and the higher the pH value, the more basic the solution.
To calculate the pH of pure water or a neutral solution, follow these steps:
1. Identify the concentration of H+ ions in the solution. In pure water, this concentration is 1 x 10^-7 moles per liter since the concentration of H+ ions is equal to OH- ions in neutral solutions.
2. Use the formula pH = -log[H+], where [H+] represents the concentration of H+ ions. In this case, pH = -log(1 x 10^-7) = 7.
Therefore, the pH of pure water or a neutral solution is 7.