Calculating the pH of solutions

We calculate the pH of solutions of weak bases in the same way as we calculate the pH of solutions of weak acids—by using an equilibrium table. The protonation equilibrium is given in Eq. 9. To calculate the pH of the solution, we first calculate the concentration of OH ions at equilibrium, express that concentration as pOH, and then calculate the pH at 25°C from the relation pH + pOH = 14.00. For very weak or very dilute bases, the autoprotolysis of water must be taken into consideration. 

Calculate the pH of solutions with the following OH moles/liter)... 

We calculate the pH of solutions of weak bases in the same way we calculate the pH of solutions of weak acids—by using the equilibrium table technique. The protonation equilibrium is... 

June 3, 1978, Lynn, Massachusetts, USA - Feb. 10, 1942 Boston, USA) Henderson studied medicine at Harvard and was Professor of Biological Chemistry at Harvard University, Cambridge, Massachusetts, from 1904 to 1942 [i]. Henderson published on the physiological role of -> buffers [ii-vii] and the relation of medicine to fundamental science. Because he and also - Hasselbalch made use of the law of mass action to calculate the - pH of solutions containing corresponding acid-base pairs, the buffer equation is frequently (esp. in the biological sciences) referred to as -> Henderson-Hasselbalch equation. 

This log form of the expression for Ka is called the Henderson-Hasselbalch equation and is useful for calculating the pH of solutions when the ratio [HA]/[A ] is known. 

Calculating the pH of solutions of strong acids and strong bases... 

Equation 2-7 is more commonly called the Henderson-Ha.sselbalch equation and is the basis for most calculations involving weak acids and bases. It is used to calculate the pH of solutions of weak acids, weak ba.ses. and buffers consisting of weak acids and their conjugate bases or weak bases and their conjugate acids. Because the pK is a modified equilibrium constant, it corrects for the fact that weak acids do itnl completely react with water. 

Calculate the % relative error in hydronium ion concentration by using concentrations instead of activities in calculating the pH of solution of the following species using the thermodynamic constants found in Appendix 3. 

Thus far, we have not considered how to calculate the pH of solutions of salts that have both acidic and basic properties—that is, salts that are amphiprotic. Such salts are formed during neutralization titration of polyfunctional acids and bases. For example, when 1 mol of NaOH is added to a solution containing 1 mol of the acid... 

Chemists often use Henderson-Hasselbach equation to calculate the pH of solutions containing a weak acid of known pKa, provided that the other concentrations are known. Henderson-Hasselbach equation is ... 

Solutions of acid salts can be acidic or alkaline, depending on which of the above equilibria predominates. In order to calculate the pH of solutions of this type, it is necessary to take both equilibria into account. 

These simple relationships may be used to calculate the pH of solutions of each type of salt considered in section 3.4. 

Calculating the pH of solutions containing the salts of polyprotic acids is made difficult by the fact that two or more equilibria occur simultaneously. Yet for certain solutions, the calculations can be reduced to a simple form (expressions 17.10 and 17.11). 

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