Buffer Preparation Tips

• 1). Create a buffer solution by picking compounds that have a pKa (acid dissociation constant) close to the pH desired for a working solution.
  
  
• 2). Pick a buffer with a pKa lower than the working pH if the pH is suppose to decrease during the experiment.
  
  
• 3). Pick a buffer with a pKa higher than the working pH if the pH is suppose to increase during the experiment.
  
  
• 4). Use this formula to determine Ka: Ka=([H+][B-])/[HB]. B is the conjugate base of the acid HB.
  
  
• 5). Now solve for pKa. The formula is: pKa= -Log10(Ka)
  
  

Ionic Strength

• 1). Use this formula to calculate ionic strength: I=1/2 ' Ci Zi^2
  
  
• 2). Let "I" equal ionic strength of the solution. The formula in Step 1 states that ionic strength is a squared sum of concentrations and valences of all ions in the solution.
  
  
• 3). Allow the molar concentration of ions to be represented by "C." In mixed solutions, there will be several concentrations to sum. The unit is moles per liter for all ions.
  
  
• 4). Represent the ion with "i." This could be sodium, chloride, etc. For example, there will be two "Ci" for the concentration of sodium in sodium chloride and the concentration of chloride in sodium chloride.
  
  
• 5). Symbolize the valence or the oxidation number of the ions with Z. This is also known as the electrical charge of the ion. Again, the "i" indicates the ion.
  
  
• 6). Square the valences on ions.
  
  
• 7). Sum the concentrations and valences.
  
  

Example for Ionic Strength

• 1). Determine the ionic strength of 1.0 M sodium chloride (NaCl) solution.
  
  
• 2). List the concentrations and valences to reduce confusion. Therefore, Na+= 1.0M and Cl-= 1.0M
  
  
• 3). Input this information into the formula and solve. For example:
  
  I (ionic strength)= ½ (1*1 (squared)+ (1*1 (squared))
  
  I=1