What is neutralization in chemistry. What is a neutralization reaction. External manifestations of neutralization
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=…;
in) 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 Russia 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
Types of neutralization reactions. The reaction itself implies the extinguishing of foci (microbes, acids and toxins).
Neutralization reaction in medicine
The neutralization reaction is used in microbiology. This is based on the fact that some compounds are able to bind pathogens of various diseases, or their metabolisms. As a result, microorganisms are deprived of the opportunity to use their biological properties. This also includes the inhibition reactions of viruses.Neutralization of toxins occurs according to a similar principle. Various antitoxins are used as the main component, which block the action of toxins, preventing them from showing their properties.
Neutralization reaction in inorganic chemistry
Neutralization reactions are one of the foundations of the inorganic. Neutralization refers to a type of exchange reaction. The reaction yields salt and water. Acids and bases are used for the reaction. Neutralization reactions are reversible and irreversible.irreversible reactions
The reversibility of the reaction depends on the degree of dissociation of the constituents. If two strong compounds are used, then the neutralization reaction will not be able to return to the original substances. This can be seen, for example, in the reaction of potassium hydroxide with nitric acid:KOH + HNO3 – KNO3 + H2O;
The neutralization reaction in a particular case turns into a salt hydrolysis reaction.
In ionic form, the reaction looks like this:
H(+) + OH(-) > H2O;
From this we can conclude that the reaction of a strong acid with a strong base cannot be reversible.
Reversible reactions
If the reaction occurs between a weak base and a strong acid, or a weak acid and a strong base, or between a weak acid and a weak base, then this process is reversible.Reversibility occurs as a result of a shift to the right in the equilibrium system. The reversibility of the reaction can be seen when using as starting materials, for example, or hydrocyanic acid, as well as ammonia.
Weak acid and strong base:
HCN+KOH=KCN+H2O;
In ionic form:
HCN+OH(-)=CN(-)+H2O.
Weak base and strong acid:
HCl+NH3-H2O=Nh4Cl+H2O;
In ionic form:
H(+)+NH3-H2O=NH4(+)+H2O.
Weak salt and weak base:
CH3COOH+NH3-H2O=CH3COONH4+H2O;
In ionic form:
CH3COOH+NH3-H2O=CH3COO(-)+NH4(+)+H2O.
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, the more of which, 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 different 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.
Acid-base reactions are neutralization reactions
Neutralization reaction The reaction of an acid and a base to form a salt and water is called.
For example, when potassium hydroxide is added to hydrochloric acid, the following reaction occurs:
KOH + HCl \u003d KCL + H 2 O OH - + H +
The neutralization reaction proceeds irreversibly only when a strong acid interacts with a strong base, because in this case, the only weak electrolyte in the reaction mixture is the reaction product, water. If in this case the acid and base are taken strictly in stoichiometric quantities, then the environment in the resulting salt solution will be neutral.
The neutralization reaction proceeds differently with the participation of weak acids (HNO 2, CH 3 COOH, H 2 SO 3) or weak bases (NH 3 * H 2 O, Mg (OH) 2, Fe (OH) 2).
HNO 2 + KOH ↔ KNO 2 + H 2 O
HNO 2 + K + + OH - ↔ K + + NO - 2 + H 2 O
HNO 2 + OH - ↔ NO 2 - + H 2 O
According to the reduced ion-molecular reaction equation, it can be seen that in the reaction system there are weak electrolytes not only among the reaction products (H 2 O), but also among the starting materials (HNO 2), which indicates the reversibility of the reaction. However, since it is water that is the weakest electrolyte, the reaction is spontaneously strongly shifted to the right, towards the formation of salt.
Let's look at a few examples.
Example 1 Choose from the listed acids and bases: HNO 2, HNO 3, H 2 SO 3, Ba (OH) 2, LiOH, Mn (OH) 2 - those whose pairwise interactions correspond to the neutralization reaction proceeding according to the equation: H + + OH - \u003d H 2 O. write the molecular equations of possible reactions.
Answer. This process corresponds to the interaction of a strong acid with a strong base. Among the listed compounds, a strong acid is HNO 3, strong bases are Ba (OH) 2 and LiOH. The equations for possible reactions are as follows:
2HNO 3 + Ba(OH) 2 = Ba(NO 3) 2 + 2H 2 O
HNO 3 + LiOH \u003d LiNO 3 + H 2 O
Example 2 The solution contains a mixture of HCl and CH 3 COOH. What reactions and in what sequence proceed when this solution is neutralized with potassium hydroxide?
Answer. The acids contained in the solution belong to different types of electrolytes: HCl is a strong electrolyte, CH 3 COOH is a weak one. Due to the suppression of the dissociation of a weak electrolyte by a strong one, the neutralization of these acids with the gradual addition of alkali proceeds sequentially: first, OH - ions interact with free H + ions, i.e. with a strong acid, and then weak acid molecules are involved in the process. Thus, the reaction occurs first with HCl, and then with CH 3 COOH:
1) HCl + KOH \u003d KCl + H 2 O H + + OH - \u003d H 2 O
2) CH 3 COOH + KOH \u003d CH 3 COOK + H 2 O CH 3 COOH + OH - \u003d CH 3 COO - + H 2 O
Example 3 Specify the qualitative and quantitative composition of the solution obtained by adding 3.36 g of KOH to 500 ml of H 3 PO 4 solution with a molar concentration of 0.1 mol/l
Given:
ϑ (p-ra H3RO4) = 500ml = 0.5l H 3 RO 4 with KOH can form three different salts.
c (H 3 RO 4) \u003d 0.1 mol / l Let us write the equations for the formation reactions of each of
m(KOH) = 3.36 g of possible salts and note the stoichiometric
M (KOH) \u003d 56 g / mol molar ratio of reagents:
The composition of the solution? n (H 3 RO 4) n (KOH)
H 3 RO 4 + KOH \u003d KN 2 RO 4 + H 2 O 1: 1
H 3 RO 4 + 2KOH \u003d K 2 HRO 4 + 2H 2 O 1: 2
H 3 RO 4 + 3KOH \u003d K 3 RO 4 + 3H 2 O
Let us determine the amounts of reagents according to the problem data and their molar ratio:
n (H 3 RO 4) \u003d c (H 3 RO 4) * ϑ (p-ra H3PO4) \u003d 0.1 mol / l * 0.5 l \u003d 0.05 mol
n (KOH) \u003d m (KOH) / M (KOH) \u003d 3.36 g / 56 g / mol \u003d 0.06 mol
n (H 3 RO 4): n (KOH) \u003d 0.05: 0.06 \u003d 5: 6 \u003d 1: 1.2
Comparing this ratio with the molar ratios of the reagents in possible reactions, we conclude that a mixture of KH 2 PO 4 and K 2 HPO 4 is formed in the solution, since there is more alkali than is required to form the first salt, but less than is necessary to form the next .
In accordance with the excess of KOH, according to the first equation, all the acid will turn into KH 2 RO 4, while n (KH 2 RO 4) \u003d n (H 3 RO 4) \u003d 0.05 mol.
The number of moles of KOH consumed in this reaction, n 1 (KOH) \u003d n (H 3 RO 4) \u003d 0.05 mol, 0.06 - 0.05 \u003d 0.01 (mol) will remain unused. This amount of KOH will interact with KN 2 RO 4 according to the equation:
KN 2 RO 4 + KOH \u003d K 2 HRO 4 + H 2 O
Obviously, 0.01 mol KOH will transfer 0.01 KN 2 RO 4 to 0.01 mol K 2 HPO 4, while 0.05 - 0.01 \u003d 0.04 (mol) K 2 HRO 4 will remain in the solution .
Answer: 0.04 mol KH 2 RO 4 and 0.01 mol K 2 HPO 4
The interaction of an acid and a base to form a salt and water is called a neutralization reaction. Typically, such reactions proceed with the release of heat.
general description
The essence of neutralization is that the acid and base, exchanging active parts, neutralize each other. As a result, a new substance (salt) and a neutral medium (water) are formed.
A simple and clear example of a neutralization reaction is the interaction of hydrochloric acid and sodium hydroxide:
HCl + NaOH → NaCl + H 2 O.
If you dip a litmus paper into a solution of hydrochloric acid and sodium hydroxide, then it will turn purple, i.e. will show a neutral reaction (red - acidic, blue - alkaline).
A solution of two active compounds turned into water due to the exchange of sodium and chlorine, so the ionic equation for this reaction is as follows:
H + + OH - → H 2 O.
After heating the resulting solution, the water will evaporate, and table salt - NaCl will remain in the test tube.
Rice. 1. Formation of salt after evaporation.
In such reactions, water is an essential product.
Examples
Neutralization reactions can occur between strong and weak acids and alkalis. Consider two types of reactions:
