Titration

Determination of the Percent Acetic Acid in Vinegar Objectives: (1) To introduce and use the concept of solution geochemistry (2) To specifically use solution geochemistry to determine the percent of acetic acid in vinegar. (3) To prepare a standard solution by the method of titration.

Consider the following balanced chemical equations: IPPP + + OH (2) (4) (5) HCI + Noah HASPS + Noah CLC + – HASPS + – Niacin + HO Nassau + OHO acacia + OHO cases + OHO These reactions in water have one feature in common: a hydrogen ion from one impound reacts with a hydroxide ion from the other compound to form water. The compound furnishing the hydrogen ion is called an acid and the one furnishing the hydroxide ion is called a base. The metal ion (the action) of the base and the anion of the acid combine to form a salt. In this context, salt is essentially synonymous with ionic compound.

Reactions such as these are called acid-base reactions. The concepts of solution reactions and geochemistry in this experiment are applicable to any chemical reaction taking place in solution, not Just the acid base reactions indicated here. Geochemistry is the area of chemistry that deals with how much of one compound reacts with another. When compounds are mixed in amounts such that these amounts Just exactly react and none of any reactant is in excess (they are all the limiting reagent), this mixture is said to be a psychometric mixture or that psychometric amounts have been mixed.

Observation of the above balanced equations indicates that symptomatically reaction occurs so that the total number of hydrogen ions available in the amount of acid reacting is the same as the total number of hydroxide ions available in the amount of base reacting. Thus in reaction 2) above, one mole (or one molecule) of HASPS (sulfuric acid) can furnish the same number of hydrogen as the number of hydroxides that two mole (or two molecules) of Noah can furnish.

Therefore one mole of HASPS reacts with 2 moles of Noah (or one molecule of HASPS reacts with two molecules of Noah). This type of geochemistry information is obtained from any balanced chemical equation. In a solution the militarily, M, is the number of moles of solute in a liter of solution. Thus where n is the number of moles and V the volume in liters. By equation (6), the number of moles of solute in V liters of a solution of militarily M is Suppose one takes 34. 56 ml off 0. 13 M solution of sulfuric acid (HASPS).

If one has a certain volume of sulfuric acid solution, there is one volume of a given Noah solution needed such that equivalent amounts of the two reactants are mixed. Equivalent amounts are the amounts that symptomatically react (that is, none of either reactant is left over). When the amount of Noah (in solution or otherwise) needed for psychometric reaction has been added, this is called the equivalence point. In the laboratory, the determination of the volume (the amount) of Noah required to exact symptomatically with the sulfuric acid solution is done by a procedure called titration.

A burette is used to measure an accurate volume of the sulfuric acid solution into a flask. A few drops of an indicator is added and another burette is used to add the Noah solution to the sulfuric acid solution until there is a visual change in color of the solution (due to the indicator). There is a visual change in color in the solution caused by the indicator,

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a substance that changes color as close as possible to the point when the psychometric amount of Noah (in this case) has been added. When the solution changes color (the indicator changes color) this is called the endpoint of the titration.

The solution should be colorless and change to a pink color (for the phenolphthalein indicator used here) upon the addition of one drop of Noah iterant. The indicator phenolphthalein is pink in basic solutions and colorless in acid solutions. The solution for the titration of sulfuric acid with Noah changes from acidic (indicator colorless) to basic (indicator pink) at the endpoint. At the endpoint the solution is slightly basic when the iterant is a base. Other indicators have a different color change but work the same in principle. The endpoint and the equivalence point should be as nearly the same as possible.

In general for a sample of an acid which has z acid hydrogen titrated with Noah, the equation using normality, CEQ 38, is unchanged but CEQ 39 becomes CEQ 40 (40) % acid = (1 of For a sample of an acid with acid acid hydrogen titrated with a base with Sybase hydroxide ions, the percent of the acid in the sample is given by (41) (Sybase/acid)(Numb)(mom of Titration are usually used to determine the amount of a substance in a sample of a old or in a solution by determining the volume of iterant that is needed to react with the desired compound.

In order to do this, the militarily and/or normality of the iterant solution must be accurately known and the chemical reaction between them must be known. This concepts and calculations above are not restricted to acid/base reactions and can be used for other types of chemical reactions. The definition of gram equivalent weight may change, however, to keep the requirement that one equivalent react with one equivalent. See the appendix to Experiment 9 for more illustration of this. If one considers the operations above, it will become clear why solutions are used in the laboratory.

It would be difficult without using solutions to effect the reaction of the sodium hydroxide (a solid) with the vinegar sample (a liquid) and make accurate measurements in regard to how much sodium hydroxide would be required to react with a given sample of the vinegar. Using solutions makes the process much easier and convenient and is one of the reasons chemists use solutions. It does, however, require that one learn about solution concentrations and how they can relate to reaction geochemistry.

In CEQ 32, note that in reaction only one of the four hydrogen in acetic acid reacts with the Noah to give a salt and water. Not all the hydrogen in compounds will react with the hydroxide of Noah to form water. Those that will are called acid hydrogen and the acid hydrogen are written first in the formula for a compound. Thus the formula for acetic acid is HACHURE indicating that it has one acid hydrogen. The determination of which and how many of the hydrogen are acid hydrogen in a compound must be done experimentally but once this is done, the formula is written so as to indicate this.

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