• Weak Acid Ionization Constants and the Determination …
  • Experiment 4. Ionization Constants of Acids. Procedure
  • Ionization of Acids and Bases, pH and Buffers

History of Acids and Bases ABOUT Acids and Bases Acids and Alkalis Acids and Bases AMINO Acids AP Acids Properties and Examples

EXPERIMENT 10 TITRATION OF ACIDS AND BASES IONIZATION CONSTANTS: ..

Ionization of Acids and Bases, ..

Concept Determination of the Dissociation Constant of a Weak Acid Pre Lab Questions Data Trial 2 1
Photo provided by Flickr
Nyasulu, F.; Moehring, M.; Arthasery, P.; Barlag, R. Determination of the Acid and Base Constants, Ka and Kb, from pH and Conductivity Measurements: A General Chemistry Laboratory Exercise. Journal of Chemical Education, 2011, 88, p. 640-642.

Determination of acid ionization constants for weak …

STEP 1 Write the equation for the ionization of the weak acid in water
Photo provided by Flickr
A good EEI may be to look at the effect of drink acids on teeth. Teeth are a form of hydroxyapatite Ca5(PO4)3(OH) but you can simulate this in the lab with calcium carbonate (marble chips). The problem is: you need to control the type of acid, whether it is phosphoric acid as found in cola drinks, or citric acid as found in lemonade. A study by (2004) found that the rate of enamel dissolution of teeth was not dependent on pH but may be affected by titratable acidity. Remember that weak acids (phosphoric, citric) are not fully dissociated in water (so their pH is not that low) but they gradually release more hydrogen ions as they react. The "titratable acidity" will be a measure of this. Citric acid, for instance, is a tribasic acid which releases its H+ ions in four steps. It has a reversible reaction with CaCO3 and the reaction is controlled by diffusion of reaction products away from the 'tooth' surface; thus, consider keeping it stirred.

 

Ionization Constants of Organic Acids

Rapid Determination of Ionization Constants (p K a ) …
Photo provided by Flickr
A good EEI would be to use fresh grape juice or simulate grape juice with 150-250 g/L glucose (or an equal mix of glucose and fructose), adding a controlled amount of yeast and wine acids and fermenting to stillness at constant temperature.

Rapid Determination of Ionization Constants ..
Photo provided by Flickr
UNDER LOAD: What I did next was to try the same experiment but with the cell under load. That way the salt bridge would be the route for the internal migration of ions. Look at it this way: a cell has an internal ohmic-equivalent resistance. The salt bridge is a resistive path for the flow of ions. Ions, plus their hydration shells and possible coordination shells, have low drift velocities through a medium. The salt bridge can constrain the ion current of the cell and its material equilibrium rate. A poor salt bridge by length, diameter, concentration, and permeability will increasingly adversely affect a cell's current and voltage as discharge rate increases. Under a load resistor, the voltages for a single salt bridge was 0.70 V and for 5 bridges it was 0.92 V. So that seemed to work.


Dissociation Constants Of Organic Acids And Bases

Validity in the context of epidemiological research involving biomarkers can be defined as the relation of the biomarker test (the potentially mismeasured biomarker) to true biomarker in the population of interest. Parameters that describe the measurement error in the population are called measures of validity (White, 1997). Two indicators of measurement error are used to describe the validity of an observed measurement compared with the true measurement (Armstrong et al., 1994). The first is systematic error or bias that would occur on average for subjects measured. The second is subject error, which is additional error that varies from subject to subject. The subject error is also called imprecision or the measure of the variation of measurement error in the population. Precision can be assessed by a construct known as the validity coefficient. It ranges from 0 to 1 with the value one indicating that the observed measurement is a perfectly precise indicator of the true measurement (Armstrong et al., 1994). A validity study would be defined here as one in which a sample of individuals is measured twice: once using the biomarker test of interest and once using a perfect measure of the true biomarker (White, 1997). However, for most biomarkers such perfect measures of the true biomarker do not exist, and, in practice, validation of a method must rely on comparison to other (similarly unvalidated) methods. Then the indicator of biomarker measurement error from the validity study can be applied to what is known about the association under study in the parent study to estimate the effects of biomarker error on the association of interest (White, 1997). While the impact of measurement error on exposure-disease associations has been studied extensively, the impact on estimates of interaction of two or more risk factors has been studied less thoroughly (Greenland, 1993). Assessment of interaction of multiple exposures, gene-environment or gene-gene is an important issue in environmental epidemiology and all the more important with biomarkers depicting mechanistic events.

Weak Acid Ionization Constants and the ..

* A. Avdeef, J. Pharmaceut. Sci. 1993, 82, 183-190; pH-Metric logP.2. Refinement of Partition Coefficients and Ionization Constants of Multiprotic Substances.