Reaction neutralization

So far we have considered the stoichiometry of reactions in solution that result in the formation of a precipitate. Another common type of solution reaction occurs between an acid and a base. We introduced these reactions in Chapter 8. Recall from that discussion that an acid is a substance that furnishes H+ ions. A strong acid, such as hydrochloric acid, HCl, dissociates (ionizes) completely in water. 

Strong bases are water-soluble metal hydroxides, which are completely dissociated in water. An example is NaOH, which dissolves in water to give Na and OH ions. 

An acid-base reaction is often called a neutralization reaction. When just enough strong base is added to react exactly with the strong acid in a solution, we say the acid has been neutralized. One product of this reaction is always water. The steps in dealing with the stoichiometry of any neutralization reaction are the same as those we followed previously. 

What does it mean to say an acid has been neutralized  

Solution Stoichiometry Calculating Volume in Neutralization Reactions 

OBJECTIVE To learn how to do calculations involved in acid-base reactions. 

When a strong acid and a strong base react, the net ionic reaction is 

When acidic and basic solutions containing hydroxide are mixed, a neutralization reaction occurs in which the acid and 

For complete neutralization to take place, the proper amounts of acid and base must be present. The salt formed in the above reaction is NaCl. If the water were evaporated after completing the reaction, we would be left with common table salt. Sodium chloride is just one of hundreds of salts that form during neutralization reactions. While we commonly think of salt, NaCl, as a seasoning for food, in chemistry a salt is any ionic compound containing a metal cation and a nonmetal anion (excluding hydroxide and oxygen). Some examples of salts that result from neutralization reactions include potassium chloride (KCl), calcium fluoride (CaF ), ammonium nitrate (NH NOj), and sodium acetate (NaC2H302). 

The reactions in Table 13.8 show that carbon dioxide is a common product in many neutralization reactions. This is clearly displayed when a drop of vinegar (acetic acid) is added to baking soda (sodium bicarbonate). Some aspirin includes an antacid in their formulation to neutralize some of the acidity imparted by the aspirin (acetylsalicylic acid). These are commonly referred to as buffered aspirins. 

Product Active Ingredient Active Ingredient Formula Neutralizing Reaction 

Alka-Seltzer Sodium bicarbonate NaHCOs H3O+ HCOa + — CO2 + 2H2O 

One of the most important reactions of acids and bases is neutralization, first introduced in Qiapter 7. When an acid and a base are mixed, the H aq) from the acid combines with the OH ( q ) from the base to form H20(l). For example, consider the reaction between hydrochloric acid and potassium hydroxide. 

Acid-base reactions generally form water and a salt— an ionic compoimd— that usually remains dissolved in the solution. The salt contains the cation from the base and the anion from the acid. 

Ionic compound that contains the cation from the base and the anion from the acid 

A slightly different but common type of neutralization reaction involves an acid reacting with carbonates or bicarbonates (compounds containing or 

HCOj ). This type of neutralization reaction produces water, gaseous carbon dioxide, and a salt. As an example, consider the reaction of hydrochloric acid and sodium bicarbonate. 

Neutralization means that relatively stronger acids and bases are combining to becoming relatively weaker acids and bases. In neutralization reactions, water-which is both a weak acid and a weak base-is often formed. 

In a typical acid-base reaction, what mainly happens is the transfer of H+ from the acid to the base. When equal amounts of a strong acid are mixed with a strong base, the result is neutrahzation. The resulting solution is much less acidic or basic than either of the original solutions in fact, the resulting solution could be neutral, that is, neither acidic nor basic. The reaction between nitric acid and sodium hydroxide is an example of just such a reaction, as shown by the following equation  

The reaction of an acid with a base to the destruction of the properties of both is a neutralization, and H20 (an unionized product) results. Thus, the following equations represent neutralization reactions because the acidic and basic properties of the reactants are removed  

As a result of the ionization of acids and bases in water, the essential reaction in each case can be shown as 

In the Br0nsted description of acids and bases, an acid is a proton donor and a base is a proton acceptor. Therefore, the reaction 

According to the Lewis theory of acids and bases (to be discussed in detail in Chapter 5), an acid is an electron pair acceptor and a base is an electron pair donor. Accordingly, the following reactions are acid-base reactions because they represent processes in which electron pair donation and acceptance occurs  

In the first two of these reactions, BC13 behaves as a Lewis acid because the boron atom has only three pairs of electrons surrounding it in the BC13 molecule so it functions as an electron pair acceptor. Typical of most ions of transition metals, Cu2+ readily accepts electron pairs from NH3 molecules. 

Carboxylic acids react with bases in the same way as inorganic acids do to form salt and water. Because carboxylic acids are weak acids, their salts hydrolyse in solution and so carboxylic acid salt solutions show basic properties. 

Material Beakers, test tubes, burette, magnetic stirrer, measuring equipment for electrical conductivity, graduated cylinder, burner diluted hydrochloric acid solution, 0.1 M sodium hydroxide solution, phenolphthalein, universal indicator paper. 

Procedure (a) In the preliminary test, add a few drops of phenolphthalein solution to 10 ml of sodium hydroxide solution until it becomes wine-red, then add hydrochloric acid until the indicator color changes. Heat part of the 

Tip The concentration of hydronium ions can be calculated from the amount of the known concentration of the sodium hydroxide solution. The concentration of hydroxide ions can be confirmed by taking the pH value by a pH meter. 

If a computer is available with all needed equipment and the conductivity tester can be connected, the conductivity curve can be obtained directly on the screen. The same is possible for pH measurements with the pH meter to obtain the curve of the pH values during titration. 

Step 3 The balanced equation tells us that one Ba ion reacts with one CtO/ ion. Because the number of moles of Cr04 - ions (2.65 x 10 ) is smaller than the number of moles of Ba ions (3.50 X 10 ), the Cr04 will run out first. 

Step 5 The mass of BaCr04 formed is obtained from its molar mass (253.3 g) as follows  

When aqueous solutions of Na2S04 and Pb(N03)2 are mixed, PbS04 precipitates. Calculate the mass of PbS04 formed when 1.25 L of 0.0500 M Pb(N03)2 and 2.00 L of 0.0250 M Na2S04 are mixed. 

Hint Calculate the moles of Pb and SO42- in the mixed solution, decide which ion is limiting, and calculate the moles of PbS04 formed. 

---

Ferguson E E 1972 Review of laboratory measurements of aeronomic ion-neutral reactions A/ / . Geophys. 28 389... 

Adams N G and Smith D 1976 The selected ion flow tube (SIFT) a technique for studying ion-neutral reactions Int J. Mass Spectrom. Ion Phys. 21 349... 

Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Adv. At Mol. Phys. 24 1-49... 

Cordonnier M, Uy D, Dickson R M, Kew K E, Zhang Y and Oka T 2000 Selection rules for nuclear spin modifications in ion-neutral reactions involving Hg" J. Chem. Phys. 113 3181-93... 

Figure Bl.7.12. A schematic diagram of a typical selected-ion flow (SIFT) apparatus. (Smith D and Adams N G 1988 The selected ion flow tube (SIFT) studies of ion-neutral reactions Advances in Atomic and Molecular Physics vol 24, ed D Bates and B Bederson p 4. Copyright Academic Press, Inc. Reproduced with pennission.)...

This preparation is an example of the use of di-M-butyl ether as a solvent in the Grignard reaction. The advantages are it is comparatively inexpensive, it can be handled without excessive loss due to evaporation, simple distillation gives an ether free from moisture and alcohol, and the vapour does not form explosive mixtures with air. n-Butyl ether cannot, of course, be employed when the boiling point of the neutral reaction product is close to 140°. 

Chaise-inversion reaction. An ion/neutral reaction wherein the charge on the reactant ion is reversed in sign. 

Ion energy loss spectrum. A spectrum that shows the loss of translation energy among ions involved in ion/neutral reactions. 

Ionizing collision. An ion/neutral reaction in which an electron or electrons are stripped from the ion and/or the neutral species in the collision. Generally, this term describes collisions of fast-moving ions or atoms with a neutral species in which the neutral species is ionized. Care should be taken to emphasize if charge stripping of the ion has taken place. 

Ion/neutral reaction. Interaction of a charged species with a neutral reactant to produce either chemically different species or changes in the internal energy of one or both of the reactants. 

Partial charge-transfer reaction. An ion/neutral reaction that reduces the charge on a multiply charged reaction ion. 

Translational spectroscopy. A technique to investigate the distribution of the velocities of product ions from ion/neutral reactions. 

Aqueous solutions of caustic soda aie highly alkaline. Hence caustic soda is ptimatily used in neutralization reactions to form sodium salts (79). Sodium hydroxide reacts with amphotoric metals (Al, Zn, Sn) and their oxides to form complex anions such as AlO, ZnO. SnO ", and (or H2O with oxides). Reaction of AI2O2 with NaOH is the primary step during the extraction of alumina from bauxite (see Aluminum compounds) ... 

Trisodium citrate is more widely used than any of the other salts of citric acid. It is generally made by neutralization of a water solution of citric acid using sodium hydroxide. The neutralization reaction is highly exothermic giving off 1109 J/g of citric acid. To conserve energy, the heat evolved can be used in the sodium citrate concentration and crystallization steps. 

Neutralization Acidic or basic wastewaters must be neutrahzed prior to discharge. If an industry produces both acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH levels. Equahzation basins can be used as neutralization basins. When separate chemical neutralization is required, sodium hydroxide is the easiest base material to handle in a hquid form and can be used at various concentrations for in-line neutralization with a minimum of equipment. Yet, lime remains the most widely used base for acid neutr zation. Limestone is used when reaction rates are slow and considerable time is available for reaction. Siilfuric acid is the primary acid used to neutralize high-pH wastewaters unless calcium smfate might be precipitated as a resmt of the neutralization reaction. Hydrochloric acid can be used for neutrahzation of basic wastes if sulfuric acid is not acceptable. For very weak basic waste-waters carbon dioxide can be adequate for neutralization. 

Aminoacridine hydrochloride monohydrate (Acramine yellow, Monacrin) [52417-22-8] M 248.7, m >355 , pKj 4.7, pKj 9.99. Recrystd from boiling H2O (charcoal Ig in 300 mL) to give pale yellow crystals with a neutral reaction. It is one of the most fluorescent substances known. At 1 1000 dilution in H2O it is pale yellow with only a faint fluorescence but at 1 100,000 dilution it is colourless with an intense blue fluorescence. [Albert and Ritchie Org Synth Coll Vol III 53 7955 Falk and Thomas Pharm J 153 158 1944.] See entry in Chapter 4 for the free base. 

Explain what a neutralization reaction is. Write a stoichiometric expression for a common neutralization reaction (give an example other than the one used in the text). 

Hydrogenation of an llj9-hydroxy-A -3-ketone over palladium in acidic media gives predominantly the 5j9-product, a complete reversal of the neutral reaction. In strong base 5j9-products also predominate in all cases... 

They arc compounds which arc, for the most pait, insoluble m water, possess an ethereal smell, have a neutral reaction, and may be distilled. 

On this basis NH4+ salts can be considered as solvo-acids in liquid NH3 and amides as solvobases. Neutralization reactions can be followed conductimetrically, potentiometrically or even with coloured indicators such as phenolphthalein ... 

The formic acid Is distilled off, and the remainder dissolved in warm benzene and washed with a bicarbonate solution to a neutral reaction. After the benzene has been distilled off, the aminomalonic ester xylidide is obtained. This Is treated with an equal quantity of sodium ethylate and boiled with twice the theoretical quantity of tetramethylene bromide in absolute alcohol. 

A solution of 7.5 grams of retroprogesterone in 500 ml of freshly distilled tertiary butyl alcohol was refluxed with 12.75 grams of finely powdered chloranil, while stirring, for 5 hours in a nitrogen atmosphere. After cooling, 2 liters of water were added and extraction was performed three times with 200 ml of methylene dichloride. The combined extracts were then diluted with 1 liter of petroleum ether (40°-60°C) washed successively with 100 ml of diluted Na2S04, four times with 75 ml of 1 N NaOH, and then water to neutral reaction. 

The melting point of the pure nicotinic acid salt is 180°C and the yield is 75% to 80% related to the used theophylline. The substance has a nearly neutral reaction and is very readily soluble in water. 

The corrosivity of a salt solution depends upon the nature of the ions present in the solution. Those salts which give an alkaline reaction will retard the corrosion of the iron as compared with the action of pure water, and those which give a neutral reaction will not normally accelerate the corrosion rate appreciably except in so far as the increased conductivity of the solution in comparison with water permits galvanic effects to assume greater importance. Chlorides are dangerous because of the ability of the anions to penetrate otherwise impervious barriers of corrosion products. 

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

---