Neutralization reaction. Neutralization reaction: definition, examples, application What is called a neutralization reaction

In the protolytic interactions considered so far (ionization of weak electrolytes and hydrolysis of salt ions), water was an obligatory component, the molecules of which, exhibiting the properties of an ampholyte, acted either as a donor or acceptor of a proton, ensuring the occurrence of these interactions. Now consider the direct interaction of acids and bases with each other, i.e. neutralization reactions.

A neutralization reaction is a protolytic reaction between an acid and a base, which results in the formation of salt and water.

Depending on the strength of the acid and base involved, the neutralization reaction can be practically irreversible or reversible to varying degrees.

When any strong acid interacts with any strong base (alkali), due to the fact that these reagents are completely dissociated into ions, the essence of such a reaction, regardless of the nature of the reagents, is expressed by the same molecular-ionic equation:

In the process of neutralization of a strong acid with an alkali, the pH of the system changes, corresponding to the neutralization curve shown in Fig. 8.1. The neutralization curve in this case is characterized by a large and sharp pH jump near the equivalence state (Veq) - The middle of this jump corresponds to the equivalence point, at which [H + ] = [OH-] = = 1 10 -7 mol / l, i.e. pH = 7.

The characteristic features of the reaction of neutralization of a strong acid with an alkali and vice versa are:

irreversibility;

exothermicity ( H 0= -57.6 kJ/mol);

Very high speed, since only mobile ions H + and OH- interact;

The pH jump during neutralization is large and abrupt;

Equivalence point at pH = 7.

These features of the neutralization reaction between strong acids and bases ensured its wide use in analytical practice for the quantitative determination of acids and bases in the objects under study.

The most common case of a neutralization reaction is the interaction of acids and bases that differ in strength. Consider the neutralization of a weak acid HA with a strong base (alkali):

Since HA and H 2 0 are weak electrolytes, protolytic equilibrium takes place due to competition for a proton between strong bases OH- and A- and, therefore, the following features will be characteristic of this neutralization reaction:

reversibility;

The pH jump during neutralization is small and less sharp (Fig. 8.2), and with a decrease in the strength of the acid, it decreases and smoothes out;

The equivalence point is at pH > 7, since the hydrolysis reaction of the anion proceeds in the system with the formation of OH- anions, which are the greater, the weaker the acid;

V E KB), when 50% alkali is added and [HA] = [A-], the pH value in the system is numerically equal to the value RK a this weak acid.

The last position follows from the equation: pH = RK a+lg ([A-]/[ON]), according to which at [A - ] = [HA] pH = RK a(because lg([A-]/[HA]) = 0). This circumstance allows not only to determine the value RK a weak acid, but also solve the inverse problem: by value RK a determine which weak acid is in the system.

Neutralization reactions of bases of various strengths with a strong acid (Fig. 8.3) are characterized by features of equilibrium protolytic processes similar to those given above. However, you need to understand and remember that the following features are characteristic of neutralizing weak bases:

-
the equivalence point is at pH< 7 из-за проте­кающей параллельно реакции гидролиза по катиону с образо­ванием катионов Н + ;

In a state of semi-neutralization (1/2 V E KB), when 50% acid is added and [B] = [BH + ], the pH value in the system is numerically equal to the pKa value of the (BH +) conjugate acid of the given weak base.

Thus, the study of the neutralization reaction makes it possible to determine not only the content of acids and bases in the system, but also the value RK a weak electrolytes, including proteins, as well as their isoelectric points.

Neutralization reactions (the process of interaction between an acid and a base) are accompanied by a thermal effect. The result is salt and water. Neutralization reactions are irreversible only when strong acids are neutralized with strong bases.

For example:

K + + OH - + H + + Cl - = K + + Cl - + H 2 O

The irreversibility of such reactions is due to the fact that in the resulting systems the only and very slightly dissociated compound is water. The ionic form of the equation in this case has the form

H + + OH - \u003d H 2 O

The exception is such reactions that are accompanied, in addition to water, by the formation of a hardly soluble compound, for example:

Ba 2+ + 2OH - + 2H + + SO 4 2- \u003d  BaSO 4 + 2H 2 O

At the same time, if strictly equivalent amounts of a strong acid and a strong alkali participate in the reaction, then the concentrations of H + and OH - ions remain the same as in water, i.e. environment becomes neutral. It has been established that when neutralizing one equivalent of a strong acid (alkali) with one equivalent of a strong alkali (acid), 57.22 kJ (13.7 kcal) is always released. For example:

NaOH + Hcl - \u003d NaCl + H 2 O, H \u003d - 13.7 kcal

This is because the reaction of neutralization of a strong acid (alkali) with a strong alkali (acid) will always be accompanied by the formation of water, and the heat of formation of one mole of water from ions is 57.22 kJ (13.7 kcal).

When neutralizing a weak acid (alkali) with a strong alkali (acid), more or less than 57.22 kJ (13.7 kcal) of heat will be released (Table I appendix).

Examples of other types of neutralization reaction

weak acid strong base:

CH 3 COOH + KOH  CH 3 COOK + H 2 O

CH 3 COOH + OH -  CH 3 COO - + H 2 O

weak base with strong acid:

NH 4 OH + HNO 3  NH 4 NO 3 + H 2 O

NH 4 OH + H +  NH 4 + + H 2 O

3) weak base with weak acid:

NH 4 OH + CH 3 COOH  CH 3 COOHNH 4 + H 2 O

NH 4 OH + CH 3 COOH  NH 4 + + CH 3 COO - + H 2 O

In the resulting systems, the equilibrium is strongly shifted to the right, i.e. towards the formation of water, but not completely, since water in them is not the only poorly dissociated substance.

With strictly equivalent amounts, the first system has a slightly alkaline, the second - slightly acidic, and the third - a neutral reaction. In the latter case, the neutrality of the system does not mean that this reaction proceeds irreversibly, but is a consequence of the equality of the dissociation constants of NH 4 OH and acetic acid.

Exercise

Experience 1.

Neutralization of sulfuric acid with caustic soda in two stages.

1) measure 50 ml of a one-molar solution of sulfuric acid H 2 S0 4 into the calorimeter;

2) measure the temperature of the acid solution t 1 in the calorimeter;

3) quickly (and without loss) pour into the acid 25 ml of a two-molar solution of alkali NaOH from a vessel and carefully mix the resulting solution of the acid salt NaHS0 4 (volume V1);

4) determine the temperature t 2 of the solution after the reaction, which proceeds according to the equation:

H 2 SO 4 + NaOH \u003d NaHSO 4 + H 2 O H 1 \u003d? (1)

where H 1 - heat of reaction;

5) determine the temperature difference t 1 \u003d t 2 - t 1 and the volume V 1 of the resulting solution;

6) quickly add the remaining 25 ml of alkali solution to the resulting NaHSO 4 solution, mix and determine the temperature of the solution t 3 . In this case, the acid salt is converted into an average salt by the reaction:

NaHSO 4 + NaOH = Na 2 SO 4 + H 2 O H 2 =? (2)

where H 2 - heat of reaction;

7) determine the temperature difference t 2 \u003d t 3 - t 2 and the volume V 2 of the resulting solution;

8) enter the results of the experiment in table. 1;

Table 1

________________________________________________________________

| 50 | 25 | t 1 | 1.09(V1) | 5.02(v1) | H 1 |

| | 25 | t2 | 1.12(v2) | 6.28(V) | H 2 |

|________________________________________________________________|

Experience 2.

Neutralization of sulfuric acid with caustic soda in one stage.

Carry out the experiment in the following order:

1) measure 50 ml of a one-molar solution of sulfuric acid H 2 S0 4 into the calorimeter;

2) measure the temperature of the acid solution t 4 in the calorimeter;

3) quickly (and without loss) pour 50 ml of a two-molar solution of alkali NaOH from a vessel into the acid and carefully mix the resulting solution of an average salt Na 2 S0 4;

4) determine the temperature t 5 of the complete neutralization reaction solution,

H 2 SO 4 + 2 NaOH \u003d Na 2 SO 4 + 2 H 2 O: H 3 (3)

where H 3 - heat of reaction;

5) determine the temperature difference t 3 \u003d t 5 - t 4 and the volume V 3 of the resulting solution;

6) enter the results of the experiment in table. 2;

table 2 ___

_____________________________________________________________

| Solution volume, ml | Difference | Density | Heat capacity | Observed |

| __________________ | tempera- | solution, | J/(g.K) | warmth, |

| H2SO4 | NaOH | tour,  С | g/mol | | kJ/mol |

|________________________________________________________________|

| 50 | 50 | t 3 | 1.12 | C3 = 6.28 | H 3 |

|________________________________________________________________|

9) calculate the enthalpy (H 1, H 2,H 3) of the neutralization reaction using the formula:

10) calculate the total heat H 1 + H 2 of the neutralization reaction;

11) compare the value of the total heat of reaction H 1 + H 2 with the value H 3 and draw the appropriate conclusions;

12) calculate the absolute and relative errors in determining the heat of reaction (3);

13) write the reaction equation (1, 2 and 3) in the form of thermochemical equations.

Work results

Let's conduct an experiment of neutralizing sulfuric acid with caustic soda in two stages

Table1

Let's conduct an experiment of neutralizing sulfuric acid with caustic soda in one stage

according to the scheme described above, and the measurement results will be entered in the table.

Table 2

Calculate the enthalpy (H 1, H 2,H 3) of the neutralization reaction using the formula:

H = V * d * C * t * 10 * 0.001,

where H is the corresponding heat of reaction; V is the volume of the resulting salt solution, ml; d is the density of this solution, g/cm 3 ; C - specific heat capacity of the solution, J (kcal); t - the corresponding difference between the observed temperatures before the reaction and after the reaction, °C; 10 is the conversion factor for the heat of reaction per equivalent taken to neutralize the acid; 0.001 - conversion factor, kJ (kcal);

H 1 \u003d 75 * 1.09 * 5.02 *  * 10 * 0.001 \u003d 40.92 kJ

H 2 \u003d 100 * 1.12 * 6.28 *  * 10 * 0.001 \u003d 19.06 kJ

H 3 \u003d 100 * 1.12 * 6.28 *  * 10 * 0.001 \u003d 60.77 kJ

Let's calculate the total heat H 1 + H 2 of the neutralization reaction:

H 1 H 2 = 59.98 kJ

Comparing the value of the total heat of reaction H 1 + H 2 with the value H 3 we see that they are almost equal. This suggests that the thermal effect of a chemical reaction proceeding at constant pressure or at constant volume does not depend on the reaction path, but depends only on the nature of the initial and final substances and their state (Hess's law).

Let us calculate the absolute and relative errors in determining the heat of reaction (3).

The standard heat of formation of a mole of water is H 0 = 57.22 kJ.

Absolute error in determining the heat of reaction:

|H 3 -H 0 | = |60.77 – 57.22| = 3.55 kJ.

Relative error in determining the heat of reaction:

|H 3 -H 0 | / H 0 \u003d 3.55 / 57.22 \u003d 6.2%

Let us write the reaction equations (1, 2 and 3) in the form of thermochemical equations:

H 2 SO 4 + NaOH \u003d NaHSO 4 + H 2 O, H 1 \u003d 41 kJ;

NaHSO 4 + NaOH = Na 2 SO 4 + H 2 O, H 2 = 19 kJ;

H 2 SO 4 + 2NaOH \u003d Na 2 SO 4 + 2H 2 O, H 3 \u003d 61 kJ.

Conclusion on work

The basic principle on which all thermochemical calculations are based was established in 1840 by the Russian chemist, Academician G. I. Hess. This principle, known as the Hess law and being a special case of the law of conservation of energy, can be formulated as follows: “The thermal effect of a reaction depends only on the initial and final states of substances and does not depend on the intermediate stages of the process. And we proved this when preparing a solution of sodium sulfate from sulfuric acid solutions of sodium hydroxide in two ways.

Outcome:

According to Hess' law, the thermal effect is the same in both cases.

Neutralization- a chemical reaction that occurs between two compounds that have the properties of an acid and a base. As a result of their interaction, the properties of both substances are lost, which leads to the release of salt and water.

Scope of neutralization

Calculations on this reaction are especially often used:

• in agrochemical laboratories;
• in chemical production;
• when handling waste.

The neutralization method is used in clinical laboratories to determine the buffer capacity of blood plasma, the acidity of gastric juice. It is also actively used in pharmacology, when it is necessary to carry out a quantitative analysis of inorganic and organic acids. This process can be carried out according to all correctly composed equations.

External manifestations of neutralization

The process of acid neutralization can be observed if, first, a few drops of an indicator are added to the solution, which will change the color of the solution. When alkali is added to this mixture, the color disappears completely. But it should be taken into account that the indicators change their color not strictly at the equivalent point, but with a deviation. Therefore, even with the correct choice of the indicator, an error is allowed. If it was chosen incorrectly, then all the results are distorted.

In the conditions of the school curriculum, citric acid and ammonia are used for this. As an example, consider the reaction process between hydrochloric acid and caustic soda. As a result of their interaction, a well-known solution of edible salt in water is formed. The following can also serve as indicators:

• methyl orange;
• litmus;
• methyl red;
• phenolphthalein.

It should be noted that the reverse reaction of neutralization is called hydrolysis. Its result is the formation of a weak acid or base.

When choosing a neutralizing agent, the following must be taken into account:

• industrial properties of the compound;
• availability;
• cost price.

Previously, magnesium oxide was used as a neutralizer. Now it is not popular because it has a high cost and reacts rather slowly.

Types of neutralization reactions

In the process of interaction of a strong base with the same strong acid, the reaction shifts towards the formation of water. However, this process does not reach the end, since salt hydrolysis begins.

When a weak acid is neutralized with a strong base, the reaction is reversible. As a rule, in such systems the course of the reaction is shifted towards the formation of salt, since water is a weaker electrolyte than, for example, hydrocyanic acid, acetic acid or ammonia.

The rate of the neutralization process varies depending on the specifics of the substances used. For example, when using NaOH, the required degree of acidity appears almost immediately. CaO leads to the desired reaction only after 15-20 minutes, and MgO - after 45 minutes. Moreover, in the last two cases, the strongest decrease in acidity is observed in the first 5 minutes after the neutralizing agent has been introduced. If the rate of the process is not very high, then secondary oxidation begins to slow it down even more.

Heat generation during the neutralization process

Often this happens under the influence of nitric acid. The higher the amount, the more heat is released. When salt is obtained, exposure to heat leads to undesirable consequences, since it begins to decompose with the release of chlorine. Due to the release of heat, it can be said that all neutralization reactions are exothermic. Its release occurs due to the difference between the total energy of H+ and OH- ions, as well as the energy of formation of water molecules.

Lesson topic: "Neutralization reaction as an example of an exchange reaction"

The purpose of the lesson: to form an idea of ​​the neutralization reaction as a particular case of the exchange reaction.

Tasks:

Create conditions for the development of ideas about the neutralization reaction as a particular case of the exchange reaction;

To expand students' knowledge of the properties of acids and bases;

Continue developing the skills of compiling equations of chemical reactions;

To cultivate observation and attention during the demonstration experiment.

Lesson type : combined

Equipment and reagents : hydrochloric acid, solutions of sodium hydroxide, copper (II) hydroxide, phenolphthalein, test tubes.

During the classes

Organizing time.

Guys, let's continue our journey through the country called Chemistry. In the last lesson, we got acquainted with the city called Foundations and its inhabitants. The main inhabitants of this city are the foundations. Define the term "foundation". Well, now let's check how you did your homework.

Checking homework.

№ 7, 8.

Questioning and further updating of knowledge.

What classes of inorganic substances do you know?

Define the terms "oxides", "acids", "salts".

What substances does water react with?

What substances are formed when water reacts with basic and acidic oxides?

How to prove that acid is formed as a result of the interaction of water with an acidic oxide?

What are indicators?

What indicator are you talking about?

From alkali I am yellow, as in a fever,

I blush from acids, as from shame.

And I'm looking for saving moisture

So that Wednesday could not seize me.

(Methyl orange)

To get into acid is a failure for him,

But he will endure without a sigh or cry.

But in the alkalis of such a blond

Not life will begin, but solid raspberries.

(Phenolphthalein.)

What other indicators do you know?

Define the terms "acidic oxide", "basic oxide".

What groups are bases divided into?

What color is phenolphthalein, methyl orange, litmus in alkali solution?

Learning new material.

You already know that alkalis are soluble bases, when working with them, special rules of safe behavior must be observed, since they have a corrosive effect on our skin. But they can be "neutralized" by adding an acid solution to them - to neutralize. And the topic of today's lesson: "Neutralization reaction as an example of an exchange reaction" (recording the topic on the board and in a notebook).

The purpose of today's lesson: to form an idea of ​​\u200b\u200bthe neutralization reaction; learn to write the equations of neutralization reactions.

Let's remember what types of chemical reactions you already know. Define reaction data type

Na 2 O + H 2 O = 2 NaOH

2H 2 O = 2H 2 +O 2

Zn + 2HCl = ZnCl 2 +H 2

Define these types of reactions.

You also already know that if phenolphthalein is added to alkali, the solution will turn crimson. But if an acid is added to this solution, the color disappears (dem. interactionsNaOHAndHCl). This is a neutralization reaction.

Write the equation on the board:NaOH + HCl=NaCl+H 2 O

The result is salt and water.

Let's all together try to define a neutralization reaction.

The neutralization reaction does not belong to any of the hitherto known types of reactions. This is an exchange reaction. General scheme of the exchange reaction: AB + CD = AD + CB

That is, it is a reaction between complex substances, during which they exchange their constituent parts.

And who knows what acid is in our stomach? Why do you think it is recommended for heartburn, if there is no pill at hand, to drink a little soda solution?

The fact is that a soda solution also has an alkaline environment, and when we drink this solution, a neutralization reaction occurs. A solution of soda neutralizes the hydrochloric acid found in our stomach.

Do you think insoluble bases react with acids? (Student answers). Dem. Cu(OH) interactions 2 And HCl .

Write the equation on the board:Cu(OH) 2 + 2 HCl = CuCl 2 + 2 H 2 O.

Anchoring

Add the following reaction equations:

A) KOH+ H 2 SO 4 = …;

b) Fe(OH) 2 + HCl=…;

V) Ca(OH) 2 + H 2 SO 4 =…. .

What initial substances must be taken to obtain the following salts by neutralization reaction:Ca( NO 3 ) 2 ; NaI; BaSO 4.

Substances given:HCl; H 2 SO 4 ; Fe( Oh) 3 . Write equations for all possible neutralization reactions between them.

Physical education: The teacher shows the substances, and the students need to determine which class of substances the substance belongs to and perform the following actions: oxide - hands up, salt - stand up, acid - hands to the sides, bases - do nothing.

Generalization

Complete the proposed scheme

Main classes of inorganic substances

SO 2 ; Na 2 Oh? ? ?

H 2 SO 4 ; HCl NaOH;Ca(OH) 2 CaCl 2; Na 2 SO 4

2. Complete the sentences below:

A group of OH atoms is called...

The valency of this group is constant and equal to ....

Bases are made up of atoms.... and one or more... .

The chemical properties of bases include their effect on .... At the same time, the indicators acquire color: litmus - ....; phenolphthalein - ....; methyl orange - ....

In addition, the bases react with .... .

This reaction is called...

The products of this reaction are... And …. .

An exchange reaction is a reaction between... substances, in which they exchange their ... parts.

The neutralization reaction is a special case of the reaction ....

VII Reflection

What did you learn in today's lesson? Have we reached the goals set in the lesson?

Homework: § 33 No. 6, prepare for practical work No. 6

Additional Information:Did you know that the women of Ancient Rus' washed their hair with a solution of spruce ash or sunflower ash? The ash solution is soapy to the touch and is called "lye". Such a solution has an alkaline environment, like the substances that we study. Ash in Arabic is al-kali.

The historical names of the most important alkalis: sodium hydroxide - caustic soda, potassium hydroxide - caustic potash. Alkalis are used to make glass and soap.

Mystery:

It contains metal and oxygen,

Plus hydrogen.

And this combination

Call -….. (bottom)

Leonid Chueshkov

Ahead is always here "ash",

And what is left behind.

She stings and stings.

And at first glance it is simple,

And it's called - ... (acid)

Leonid Chueshkov