pH and Titration Flashcards
Total acidity and titratability
The total amount of acid in foods is measured by the amount dissociated and nondissociated acid. It is a good indicator of how much the acid will impact the flavor of a food.
pH, ka, and pka
The pH is equal to number of H+ ions freely moving around in a food ready to chemically react with other compounds. It is a good indicator of how well microbes will grow in a food. Ka is the equlibrium of a buffer solution and is expressed as (Cojugate acid)(conjucate base)/(undissociated Acid) when the conjugate acid and base are present along with an undissociated acid in solution. The pka is the pH at which the conjugate acids and bases are in equal concentration to the undissociated acid.
electrode, and pH meter
A pH meter is also known as a potentiometer or a unit where two electrodes, an indicator electrode and a reference electrode are placed in a sample solution. The flow of H30+ ions into the indicator electrode causes changes in electrical potential energy or energy released by electrons as they flow through the indicator column which will lead to a change an overall change in the electrode potential of a sample. The change in electrode potential of a sample can be calculated by the NERST equation N=E0 multiplied by RST. The calculated electrode poteintial can then be converted to a corrosponding pH value.
NERST equation:
N=E0+2.303(RT/NF)log(A)
N= number of charge on ion
E0=Electrode potential
Electrodes: calomel electrode, and combination electrodes
Calomel electrodes: Most popular form of reference electrodes which contains the equation Hg2Cl2 +2e»> 2Hg +2Cl-( where electrical current comes from). Platinum wire covered with Hg2Cl2 electrical current passes through. Surrounding the wire is saturated KCl solution which slowly enters into a permeable junction or opening gap into the sample solution (purpose?).
Combination electrode: Most popular type of electrode, consists of instruments to measure pH, changes in electrode potential and temperature. It must be calibrated or adjusted to three different pH’s each three intervals apart in buffer solutions of those pH values and the sample solution must be placed 2cm below the KCl saturated solution in the reference electrode.
