Acid-base reactions equivalent mass

Equivalent weight in acid-base reactions The mass of an acid or base that furnishes or reacts with 6.022 X 10 H3O+ or OH ions. 

The equivalent is defined in terms of a chemical reaction. It is defined in one of two different ways, depending on whether an oxidation-reduction reaction or an acid-base reaction is under discussion. For an oxidation-reduction reaction, an equivalent is the quantity of a substance that will react with or yield 1 mol of electrons. For an acid-base reaction, an equivalent is the quantity of a substance that will react with or yield 1 mol of hydrogen ions or hydroxide ions. Note that the equivalent is defined in terms of a reaction, not merely in terms of a formula. Thus, the same mass of the same compound undergoing different reactions can correspond to different numbers of equivalents. The ability to determine the number of equivalents per mole is the key to calculations in this chapter. 

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

MCAT 1 MORGAN if. Chemistry Remember that solution concentrations are always given in terms of the form of the solute before dissolution. For instance, when 1 mole of NaCl is added to 1 liter of water, it is approximately a 1 molar solution and NOT a 2 molar solution even though each NaCl dissociates into two ions. Normality measures the number of equivalents per liter of solution. The definition of an equivalent will depend upon the type of reaction taking place in the solution. The only time normality is likely to appear on the MCAT is with an acid-base reaction. In an acid-base reaction an equivalent is defined as the mass of add or base that can furnish or accept one mole of protons. For instance, a 1 molar solution of H2S04 would be called a 2 normal solution because it can donate 2 protons for each h2so4. 

For example, one mole of H2SO4 in an acid-base reaction supplies two moles of H+. The mass of one equivalent of H2SO4 is half of the mass of one mole of H2SO4, and its normality is twice its molarity. In a redox reaction (see competency 9), an equivalent is the quantity of substance that gains or loses one mol of electrons. 

Normality is another unit of concentration that is sometimes used, especially when dealing with acids and bases. The use of normality focuses mainly on the H and OH" available in an acid-base reaction. Before we discuss normality, however, we need to define some terms. One equivalent of an acid is the amount of that acid that can furnish 1 mol ofH ions. Similarly, one equivalent of a base is defined as the amount of that base that can furnish 1 mol ofOH ions. The equivalent weight of an acid or a base is the mass in grams of 1 equivalent (equiv) of that acid or base. 

Another concentration measure sometimes encountered is normality (symbolized by N). Normality is defined as the number ot equivalents per liter of solution, where the definition of an equivalent depends on the reaction taking place in the solution. For an acid-base reaction, the equivalent is the mass of acid or base that can furnish or accept exactly 1 mole of protons (H ions). In Table 11.2 note, for example, that the equivalent mass of sulfuric acid is the molar mass divided by 2, since each mole of H2SO4 can furnish 2 moles of protons. The equivalent mass of calcium hydroxide is also half the molar mass, since each mole of Ca(OH)2 contains 2 moles of OH ions that can react with 2 moles of protons. The equivalent is defined so that 1 equivalent of acid will react with exactly 1 equivalent of base. 

One equivalent mass of an acid neutralizes one equivalent mass of a base. It is important to note that the equivalent mass of a polyprotic acid is not invariant for H3PO4 it may be the gram formula mass, one half this, or one third, depending on whether one, two, or three hydrogens are effective in the reaction under consideration. 

In ordinary acid-base reactions there are one, two, or three equivalents per mole. It follows that the equivalent mass of an acid or a base is the same as, one half of, or one third of the molar mass. The molar mass of phosphoric acid is 97.99 g/mol. For the three reactions of phosphoric acid (Equations 16.6, 16.7, and 16.8), the equivalent masses are... 

In the case of an acid-base reaction,/eq is chosen in such a way that only one proton exchange is considered during the titration reaction. For example, hydrochloric acid can liberate only one proton per mole. Hence, its equivalent is equal to its molar mass, and its equivalent factor is equal to 1 ... 

Titrations can be carried out in cases in which the solubility relations are such that potentiometric or visual indicator methods are unsatisfactory for example, when the reaction product is markedly soluble (precipitation titration) or appreciably hydrolysed (acid-base titration). This is because the readings near the equivalence point have no special significance in amperometric titrations. Readings are recorded in regions where there is excess of titrant, or of reagent, at which points the solubility or hydrolysis is suppressed by the Mass Action effect the point of intersection of these lines gives the equivalence point. 

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. 

Titrations are widely used in analytical chemistry to determine acids, bases, oxidants, reductants, metal ions, proteins, and many other species. Titrations are based on a reaction between the analyte and a standard reagent known as the titrant. The reaction is of known and reproducible stoichiometry. The volume, or the mass, of the titrant needed to react essentially completely with the analyte is determined and used to obtain the quantity of analyte. A volume-based titration is shown in this figure, in which the standard solution is added from a buret, and the reaction occurs in the Erlenmeyer flask. In some titrations, known as coulometric titrations, the quantity of charge needed to completely consume the analyte is obtained. In any titration, the point of chemical equivalence, experimentally called the end point, is signaled by an indicator color change or a change in an instrumental response. 

The quotient of the gram formula mass of an acid by the number of hydrogen atoms which are replaceable for the reaction under consideration is called the equivalent mass of the acid. Likewise, the quotient of the gram formula mass of a base by the number of hydroxyl groups which are replaceable for the reaction under consideration is called the equivalent mass of the base. 

Given an equation for a neutralization reaction, state the number of equivalents of acid or base per mole and calculate the equivalent mass of the acid or base. 

Words that can be used as topics in essays 5% rale buffer common ion effect equilibrium expression equivalence point Henderson-Hasselbalch equation heterogeneous equilibria homogeneous equilibria indicator ion product, P Ka Kb Kc Keq KP Ksp Kw law of mass action Le Chatelier s principle limiting reactant method of successive approximation net ionic equation percent dissociation pH P Ka P Kb pOH reaction quotient, Q reciprocal rule rule of multiple equilibria solubility spectator ions strong acid strong base van t Hoff equation weak acid weak base... 

In a neutralization reaction, moles of H+ ions equal moles of OH ions. This relationship is the basis for the procedure called titration, which you will use to standardize a base solution. Standardizing a base means determining its molar concentration. You will then use your standardized base to determine the molar mass of an acid. To determine when the moles of H+ equal the moles of OH, you will monitor the pH of an acid solution as a solution of base is added slowly. The pH will rise suddenly when the concentrations of the two ions are equal (the equivalence point). 

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