PH AND CONCENTRATION OF ACID AND BASES
PH is a measure of how acidic or basic a solution is.
Solutions with higher concentrations of Hydrogen ions have low PH and are considered acidic. As the concentrations of Hydrogen ions in a solution increase the more acidic the solution becomes since the concentration of H+ is measured in PH units. Therefore this quantifies the amount of [H+] in the form of a positive number.
PH of a solution is the negative log to base 10 of Hydrogen ion concentration (H+) in moles per liter.
PH=-log [H+] (S.P.L SQ renson (1909)
Solutions with lower concentrations of H+ have higher PHs and are considered as basic. As the level of Hydroxide ions increases the more basic or alkaline the solution becomes. Thus the solution with PH greater than 7 is alkaline. OH- outnumber H+. (Bronsted and Arrhenius 1887)
A solution with PH of 5 has a concentration of 0.00001M
That is;
PH=-log [H+]
5=-log [H+]
Antilog -5=[H+]
[H+]=0.00001M
A solution with a PH of 6 has a concentration of 0.000001M
That is;
6=-log [H+]
Antilog -6=[H+]
[H+]=0.000001M
Therefore the concentration of PH 5 is higher than that of PH 6
If we compare various household solutions used below we can group them according to their PHs and [H+] Concentrations.
| Most acidic | Least acidic | |||
| Vinegar | Shampoo | Milk | water | |
| PH | 3.5 | 5.5 | 6.5 | 7.0 |
| [H+] | 10^-3 | 10^-5 | 10^-6 | 10^-7 |
Conjugate acid/base pairs are defined by proton exchange. That is the addition or subtraction of H+. (Ravi Kumar MauryaKSC; 1968)
The conjugate acid of water is hydroxonium ion, H3O+. It is formed by the association of H+ with a water molecule.
The conjugate acid of Ammonia is Ammonium ion; NH4+
The conjugate acid of SO4- is bisulfate ion; HSO4-
SO4- +H+HSO4-
The conjugate base of water is hydroxide ion (OH-)
The conjugate base of Nitric acid is Nitrate ion (NO3-)
HNO3NO3 +H+
The conjugate base of Hydrochloric acid is Chloride ion (Cl-)
REFERENCES
Atkins and Paula; Physical Chemistry; Acid and base protonations; 9th edition; 2003 pp789
Bronsted and Arrhenius; Physical Chemistry on PH scale and Concentration of solutions; 5th edition 2001; pp.756
Ravi Kumar MauryaKSC; Conjugate acid and conjugate base definitions and formation; 1968