lab manual experiment 2

lab manual experiment 2 - EXPERIMENT 2 Volumetric Analysis...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Experiment 2- Page 1 EXPERIMENT 2 Volumetric Analysis of an Organic Acid INTRODUCTION Analytical Chemistry: Volumetric Analysis In Experiment #1, the concentration of a solution of aluminum ion was determined by gravimetric analysis. Although still a commonly used method for metal ion analyses in the chemical laboratory, precipitation techniques are quite time-consuming when multiple determinations are needed. Also, the unavailability of a suitable precipitating agent for many samples limits its use. Further, as we are analyzing samples of solid acids in this experiment, precipitation is an unsuitable method in any case. A second and even more commonly used analytical method of analysis utilizes volume rather than masses: this is called volumetric analysis. Volumetric analysis involves a variety of reaction types including acid-base, oxidation- reduction, precipitation and complex ion formation. It can involve the reaction of two solutions mixed together (as is done in Experiment #4B) or the reaction of a solution with a (dissolved) solid (as is done in this experiment). This procedure is called a titration which involves the use of a piece of equipment known as a buret. To be useful in quantitative volumetric analyses, the reaction involved must be stoichiometric, fast, and must favor product formation. Titrations also tend to be performed with aqueous solutions. In titration volumetric analysis, one of the solutions used must be of an exactly known concentration. This is the solution that will be placed in the buret and is known as titrant. The titrant is then reacted with the unknown species of interest, called the analyte. The titrant solution, which is of an exactly determined concentration and of known composition, is called a standard solution. The concentration of a standard solution can be exactly determined one of two ways: 1) by measuring the exact mass of the titrant and carefully diluting it to a known volume (thus giving an exactly known concentration) or 2) by standardization (i.e. determining its composition) which involves titrating it against an exactly determined mass of a solid sample. This solid sample, called a primary standard must be: (a) readily available in pure form or in a state of known purity, (b) easy to dry and not so hygroscopic that it takes up water during the weighing process and (c) have a high molar mass to minimize the consequences of errors in weighing. It is the second method (standardization) which we will utilize in Experiment #2. Once a standard solution has been obtained as the titrant, a method of analysis is needed for detecting when stoichiometric amounts of the titrant and the analyte have reacted (this is called the stoichiometric point). A visible color change of the solution at or near the stoichiometric point is usually needed. To obtain such a color change, a third-party indicator (i.e. a compound that does not directly react with the two reactants in the titration but changes color near the stoichiometric point) is often used, especially in acid-base titrations (as in this experiment). However,
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 9

lab manual experiment 2 - EXPERIMENT 2 Volumetric Analysis...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online