Acids equivalent mass

Zeolites exhibit a considerably lower proton (acid site) concentration than liquid acids. For example, 1 g of H2SO4 contains 20 X 10-3 moles of protons, whereas 1 g of zeolite HY, with a Si/Al atomic ratio of five, contain no more than 3 X 10-3 moles of protons. (Note that this is a cmde approximation of the acidic sites available for catalysis, because it assumes that with both materials all protons are available and catalytically active.) Moreover, 1 g of H2SO4 occupies far less volume (i.e., 0.5 cm3) than the equivalent mass of zeolite (4-6 cm3). 

In an experiment to determine the equivalent mass of an unknown acid, a student measured out a 0.250-gram sample of an unknown solid acid and then used 45.77 mL of 0.150 M NaOH solution for neutralization to a phenolphthalein end point. Phenolphthalein is colorless in acid solutions but becomes pink when the pH of the solution reaches 9 or higher. During the course of the experiment, a back-titration was further required using 1.50 mL of 0.010 M HC1. 

In Part II, a weak acid is titrated with the strong base from Part I and the equivalence point will be somewhat higher than 7 (8 - 9). By titrating a known amount of solid acid with the standardized NaOH, it will be possible to determine the number of moles of ff the acid furnished. From this information, one can obtain the equivalent mass (EMa) of the acid ... 

However, the equivalent mass of the acid may or may not be the same as the molecular mass of the acid since some acids produce more than one mole of ff per mole of acid. In order to find the molecular mass from the EMa, the molecular formula is required. 

Once the student had determined the exact concentration of the base, the student then proceeded to determine the equivalent mass of an unknown acid. To do this, the student measured out 0.500 grams of an unknown solid acid and titrated it with the standardized base, recording pH with a calibrated pH meter as the base was added. The student added 43.2 mL of the base but went too far past the end point and needed to back-titrate with 5.2 mL of the 0.100 M HC1 to exactly reach the end point. 

Normality is sometimes used in acid-base or ion-exchange chemistry. With respect to adds and bases, the equivalent mass of a reagent is the amount that can donate or accept 1 mole of H+. With respect to ion exchange, the equivalent mass is the mass of reagent containing 1 mole of charge. 

The equivalent mass of an acid is that fraction of the molar mass which contains or can supply one mole of H+. A simple way of looking at the equivalent mass is that it is the mass of the acid divided by the number of H s per molecule, assuming that complete ionization occurs. 

Sometimes, the calculation involves a monoprotic acid and a dihydroxy base or another set of conditions in which the relationship is not 1 1. We have to keep track of the various concentrations so that the molarities do not get mixed up. However, stoichiometric calculations involving solutions of specified normalities are even simpler. By the definition of equivalent mass in Chapter 12, two solutions will react exactly with each other if... 

In a case like this problem, where a substance can have several equivalent masses, the normality determined by one type of reaction is not necessarily the normality in other reactions. For instance, if a weak base like NH3 were to be used instead of a strong base for neutralizing the acid, or if the method of detecting the point of neutralization were changed (a different indicator), the equivalent mass of phosphoric acid (and the normality) might well be different. 

The mass of 1.243 g of an acid is required to neutralize 31.72mL of 0.1923 N standard base. What is the equivalent mass of this acid ... 

As part of a study of the persistence of silvex in water, the PGBE ester was applied as an emulsion. The ester is distributed as a 64.5% concentrate (42.8% acid equivalent). In this study, floating masses of alligatorweed (Altemanthera philoxeroides [Mart.] Griseb.) contained in 1500-gallon plastic swimming pools, were sprayed. To simulate natural conditions, the bottoms of the pools were covered with a 4 to 5-inch thick layer of soils, the tanks were filled with water, alligatorweed was added, and the system was allowed to equilibrate for 3 months prior to treatment. Three different soil types—Piedmont, Coastal Plains, and Florida muck—taken from their representative areas in the southeastern United States, were used as discrete bottom muds. 

EXAMPLE 15.22. Calculate the molar mass of an acid with three replaceable hydrogen ions and an equivalent mass of 31.2 g/equiv, assuming complete neutralization. 

Calculate the equivalent mass of each of the following acids toward complete neutralization, (a) H3PO3, b) H2SO4, (c) HBr, d) HC2H3O2, and (e) H2C2O4. 

A sample of 5.00 g of a solid acid was treated with 50.00 mL of 2.500 N NaOH, which dissolved it completely (by reacting with it). There was enough excess NaOH to require 9.13 mL of 1.000 N HCl to neutralize the excess base. What is the equivalent mass of the acid ... 

The half-reaction and thus the equivalent mass are given in the prior problem. The 1 mol of acid liberates 2 mol of electrons, and so there are 2 equiv of acid per mole of acid. If we wrote the half-reaction for the equation given, we would find that there was 10 mol of electrons involved in reducing 5 mol of acid, and so again we get... 

Chemistry is a very wide field however, only a very small portion, indeed, of this seemingly complex subject is used in this book. These include equivalents and equivalent mass, methods of expressing concentrations, activity and active concentration, equilibrium and solubility product constants, and acids and bases. This knowledge of chemistry will be used under the unit processes part of this book. 

Equivalent mass based on acid-base reactions. In this method, the equivalent mass is defined as (Snoeyink and Jenkins, 1980) ... 

Take the two reactions of phosphoric acid with sodium hydroxide that follow. These reactions will illustrate that the equivalent mass of a given substance depends upon the chemical reaction in which the substance is involved. 

To establish the equivalence of the component alkalinities, they must all be referred to a common end point when the acid is added to the solution. From general chemistry, we learned that this is the methyl orange end point. As far as the OH ion is concerned, the end point for the reaction + OFT HOH has already been reached well before the methyl orange end point. Thus, for the purpose of determining equivalents, the reaction for the hydroxide alkalinity is simply H" -1- OH HOH and the equivalent mass of the hydroxide is OH/1. One gram equivalent of the hydroxide is then equal to one gram mole. Therefore,... 

Carbon dioxide will be used as the source of acidity in the derivation below. To determine the equivalent mass of carbon dioxide, the species it is reacting with must be known. Whatever alkalinity species are present, it is expected that carbon dioxide will react with them until the end point is reached. Since the hydroxyl ion is always present no matter what stage of pH any solution is in, the OH is the very ion that will take carbon dioxide to this end point thus, it determines the equivalent mass of carbon dioxide. 

To obtain the equivalent mass of the lime, consider that it must neutrahze the acidity first before raising the pH. Thus,... 

Similar statements also hold with respect to bases added to raise the pH. They need to react first with existing acidities before the pH can increase, and then-equivalent masses also need to be determined by referring to a single unifying species. This single unifying species is the hydrogen ion. We will discuss the hydroxide ion first. 

Let us derive the formulas for calculating the quantities of sulfuric acid, hydrochloric acid, and nitric acid and the formulas for calculating the quantities of caustic soda and soda ash that may be needed to lower and to raise the pH, respectively. To find the equivalent masses of the acids, they must be reacted with the hydroxyl ion. Reaction with this ion is necessary, since total alkalinity may be represented by the hydroxyl ion. Remember that the acids must first consume all the existing alkalinity represented in the overall by the OH before they can lower the pH. Thus, proceed as follows ... 

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