# How much OH- must be added to achieve desired pH?

• physicsnnewbie
In summary, adding 5 M KOH to 1.0 L of 0.1 M glycine at pH 9 will neutralize the -NH3+ and increase the pH to 10. Using the Henderson-Hasselbalch equation, the amount of -NH3+ can be calculated at pH 9 and 10, and then a simple stoichiometry can determine the amount of KOH needed.

## Homework Statement

Glycine which has a pKa of 9.6 can exist in protonated form (-NH3+) or as the free base (-NH2) because of the reversible equalibrium R-NH3+ <------> R-NH2 + H+.

How much 5 M KOH must be added to 1.0 L of 0.1 M glycine at pH 9 to bring the pH to exactly 10?

## The Attempt at a Solution

I have spent a couple hours trying to figure this out but don't really know where to start. A couple hints might point me in the right direction

When you add KOH to pH 9 glycine solution you are in fact neutralizing -NH3+.

Use Henderon-Hasselbalch equation to calculate amount of -NH3+ in solution at pH 9 and 10, then it is a simple stoichiometry.

## 1. How do you determine the desired pH?

The desired pH is determined based on the specific needs of the experiment or solution. It is important to consider the purpose of the solution and any potential changes that may occur during the experiment. pH can also be calculated using the Henderson-Hasselbalch equation.

## 2. What is the relationship between OH- and pH?

OH- is a base and is responsible for increasing the pH of a solution. As OH- ions are added, the pH increases towards a more basic level.

## 3. How do you calculate the amount of OH- needed?

The amount of OH- needed can be calculated using the Henderson-Hasselbalch equation or by using a pH calculator. The solution's initial pH and desired pH are used in the calculation to determine the amount of OH- needed to achieve the desired pH.

## 4. What factors can affect the amount of OH- needed?

The initial pH of the solution, the volume of the solution, and the strength of the OH- solution can all affect the amount of OH- needed to achieve the desired pH. Temperature and other chemicals present in the solution can also play a role.

## 5. Can you add too much OH- and overshoot the desired pH?

Yes, it is possible to add too much OH- and overshoot the desired pH. It is important to carefully monitor the pH while adding OH- to avoid overshooting. If this happens, the pH can be adjusted by adding an acid to neutralize the excess OH- ions.