Activity Of The H 1 Ion example essay topic
548 words
Introduction: In 1909 S.P.L. Sorensen published a paper in Biochem Z in which he discussed the effect of H 1+ ions on the activity of enzymes. In the paper he invented the term pH to describe this effect and defined it as the -log [H 1+ ]. In 1924 Sorensen realized that the pH of a solution is a function of the 'activity' of the H 1+ ion not the concentration and published a second paper on the subject. A better definition would be pH = -log [aH 1+ ], where aH 1+ denotes the activity of the H 1+ ion. The activity of an ion is a function of many variables of which concentration is one.
It is unfortunate that chemistry texts use a definition for pH that has been obsolete for over 50 years. Because of the difficulty in accurately measuring the activity of the H 1+ ion for most solutions the International Union of Pure and Applied Chemistry (IUPAC) and the National Bureau of Standards (NBS) has defined pH as the reading on a pH meter that has been standardized against standard buffers. The following equation is used to calculate the pH of all solutions: The activity of the H 1+ ion is determined as accurately as possible for the standard solutions used. The identity of these solutions vary from one authority to another, but all give the same values of pH to +/- 0.005 pH unit.
The historical definition of pH is correct for those solutions that are so dilute and so pure the H 1+ ions are not influenced by anything but the solvent molecules (usually water). In most solutions the pH differs from the -log [H 1+ ] in the first decimal point. Purpose: In this activity, we will be using red and blue lim us paper to determine whether a solution is an acid or a base. Key terms: Buffer: a substance or combination of substances capable of neutralizing limited quantities of either acid (H 3 O+) or base (OH-) added to it.
Dynamic Equilibrium: Two offsetting processes occur at equal rates, producing a state of balance where no net changes is observed. Molar Concentration or Molarity: Concentration of a solution measured as the number of moles of solute per liter of solution. For example, a 6 M HCl solution contains 6 moles of HCl per liter of solution. Hypothesis: I predict that out of the 20 solutions that we are going to be testing, about 6 of them will be an acid, 3 will be neutral and 11 will be a base. Data Table: UNKNOWN Acid or Base pH 1 Neutral 6 2 Neutral 7 3 Base 8 4 Acid 3 5 Acid 4 6 Acid 3 7 Base 9 8 Base 8 9 Acid 4 10 Neutral 6 11 Base 10 12 Base 8 13 Acid 4 14 Base 10 15 Acid 3 16 Neutral 6 17 Neutral 7 18 Acid 2 19 Base 10 20 Neutral 6 Conclusion: After working with the lim us paper to find out which solutions were Acids, Neutral and Bases, I know how to identify it on the pH scale and what the colour stands for..
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