Under appropriate conditions, glycerol undergoes hydrolysis. Hydrolysis of organic compounds

Chemistry, like most of the exact sciences that require a lot of attention and solid knowledge, has never been a favorite discipline for schoolchildren. But in vain, because with its help you can understand many processes occurring around and inside a person. Take, for example, the hydrolysis reaction: at first glance it seems that it matters only for chemical scientists, but in fact, without it, no organism could fully function. Let's learn about the features of this process, as well as its practical significance for humanity.

Hydrolysis reaction: what is it?

This phrase refers to a specific reaction of exchange decomposition between water and a substance dissolved in it with the formation of new compounds. Hydrolysis can also be called solvolysis in water.

This chemical term is derived from 2 Greek words: "water" and "decomposition".

Hydrolysis products

The reaction under consideration can occur when H 2 O interacts with both organic and inorganic substances. Its result directly depends on what the water was in contact with, and also whether additional catalyst substances were used, whether the temperature and pressure changed.

For example, the reaction of salt hydrolysis promotes the formation of acids and alkalis. And if we are talking about organic substances, other products are obtained. Water solvolysis of fats promotes the formation of glycerol and higher fatty acids. If the process occurs with proteins, various amino acids are formed as a result. Carbohydrates (polysaccharides) are broken down into monosaccharides.

In the human body, unable to fully absorb proteins and carbohydrates, the hydrolysis reaction "simplifies" them to substances that the body is able to digest. So solvolysis in water plays an important role in the normal functioning of each biological individual.

Salt hydrolysis

Having learned hydrolysis, it is worth familiarizing yourself with its course in substances of inorganic origin, namely salts.

The peculiarities of this process are that when these compounds interact with water, weak electrolyte ions in the composition of the salt are detached from it and form new substances with H 2 O. It could be either acid or both. As a result of all this, a shift in the equilibrium of water dissociation occurs.

Reversible and irreversible hydrolysis

In the example above, in the last one, you can see two arrows instead of one, and both are directed in different directions. What does it mean? This sign indicates that the hydrolysis reaction is reversible. In practice, this means that, interacting with water, the taken substance not only simultaneously decomposes into components (which allow the formation of new compounds), but also forms again.

However, not every hydrolysis is reversible, otherwise it would not make sense, since new substances would be unstable.

There are a number of factors that can contribute to such a reaction becoming irreversible:

Temperature. It depends on whether it rises or falls, in which direction the equilibrium shifts in the ongoing reaction. If it gets higher, there is a shift towards an endothermic reaction. If, on the contrary, the temperature decreases, the advantage is on the side of the exothermic reaction.
Pressure. This is another thermodynamic quantity that actively influences ionic hydrolysis. If it goes up, chemical equilibrium is shifted towards the reaction, which is accompanied by a decrease in the total amount of gases. If it goes down, vice versa.
High or low concentration of substances involved in the reaction, as well as the presence of additional catalysts.

Types of hydrolysis reactions in saline solutions

An anion (an ion with a negative charge). Solvolysis in water of acid salts of weak and strong bases. Such a reaction, due to the properties of the interacting substances, is reversible.

Degree of hydrolysis

When studying the features of hydrolysis in salts, it is worth paying attention to such a phenomenon as its degree. This word means the ratio of salts (which have already entered into a decomposition reaction with H 2 O) to the total amount of this substance contained in the solution.

The weaker the acid or base involved in hydrolysis, the higher its degree. It is measured in the range of 0-100% and is determined by the formula below.

N is the number of molecules of the substance that have undergone hydrolysis, and N 0 is their total number in solution.

In most cases, the degree of aqueous solvolysis in salts is low. For example, in a 1% sodium acetate solution, it is only 0.01% (at a temperature of 20 degrees).

Hydrolysis in substances of organic origin

The process under study can also occur in organic chemical compounds.

In almost all living organisms, hydrolysis occurs as part of energy metabolism (catabolism). With its help, proteins, fats and carbohydrates are broken down into easily digestible substances. At the same time, water itself is rarely able to start the process of solvolysis, so organisms have to use various enzymes as catalysts.

If we are talking about a chemical reaction with organic substances aimed at obtaining new substances in a laboratory or production environment, then strong acids or alkalis are added to the solution to speed up and improve it.

Hydrolysis in triglycerides (triacylglycerols)

This hard-to-pronounce term refers to fatty acids, which most of us know as fats.

They are both animal and plant origin. However, everyone knows that water is not capable of dissolving such substances, how does the hydrolysis of fats occur?

The reaction in question is called saponification of fats. This is an aqueous solvolysis of triacylglycerols under the influence of enzymes in an alkaline or acidic medium. Depending on it, alkaline hydrolysis and acid hydrolysis are released.

In the first case, as a result of the reaction, salts of higher fatty acids (better known to everyone as soaps) are formed. Thus, ordinary solid soap is obtained from NaOH, and liquid soap is obtained from KOH. So alkaline hydrolysis in triglycerides is the process of forming detergents. It should be noted that it can be freely carried out in fats of both vegetable and animal origin.

The reaction in question is the reason why soap does not wash well in hard water and does not lather at all in salt water. The fact is that hard is called H 2 O, which contains an excess of calcium and magnesium ions. And soap, once in water, again undergoes hydrolysis, decomposing into sodium ions and a hydrocarbon residue. As a result of the interaction of these substances in water, insoluble salts are formed, which look like white flakes. To prevent this from happening, sodium bicarbonate NaHCO 3, better known as baking soda. This substance increases the alkalinity of the solution and thereby helps the soap to perform its functions. By the way, in order to avoid such troubles, synthetic detergents from other substances, for example from salts of esters of higher alcohols and sulfuric acid. Their molecules contain from twelve to fourteen carbon atoms, so they do not lose their properties in salt or hard water.

If the environment in which the reaction occurs is acidic, this process is called acid hydrolysis of triacylglycerols. In this case, under the action of a certain acid, substances evolve to glycerol and carboxylic acids.

Hydrolysis of fats has another option - the hydrogenation of triacylglycerols. This process is used in some types of cleaning, for example, when removing traces of acetylene from ethylene or oxygen impurities from various systems.

Hydrolysis of carbohydrates

The considered substances are one of the most important components of human and animal food. However, sucrose, lactose, maltose, starch and glycogen in its pure form, the body is not able to absorb. Therefore, just as with fats, these carbohydrates are broken down into digestible elements through a hydrolysis reaction.

Also, aqueous solvolysis of carbons is actively used in industry. From starch, due to the reaction with H 2 O under consideration, glucose and molasses are extracted, which are part of almost all sweets.

Another polysaccharide that is actively used in industry for the manufacture of many useful substances and products is cellulose. Technical glycerin, ethylene glycol, sorbitol and well-known ethyl alcohol are extracted from it.

Hydrolysis of cellulose occurs with prolonged exposure to high temperature and the presence of mineral acids. end product this reaction is, as in the case of starch, glucose. It should be borne in mind that the hydrolysis of cellulose is more difficult than that of starch, since this polysaccharide is more resistant to mineral acids. However, since cellulose is the main component of the cell membranes of all higher plants, raw materials containing it are cheaper than for starch. At the same time, cellulose glucose is more used for technical needs, while the product of starch hydrolysis is considered better suitable for nutrition.

Protein hydrolysis

Proteins are the main construction material for the cells of all living organisms. They are composed of numerous amino acids and are very important product for the normal functioning of the body. However, being high molecular weight compounds, they can be poorly absorbed. To simplify this task, they are hydrolyzed.

As in the case of other organic substances, this reaction breaks down proteins into low molecular weight products that are easily absorbed by the body.

Hydrolysis is the exchange reaction of a salt with water ( solvolysis with water ). In this case, the original substance is destroyed by water, with the formation of new substances.

Since hydrolysis is an ion exchange reaction, its driving force is the formation of a weak electrolyte (precipitation or (and) gas evolution). It is important to remember that the hydrolysis reaction is a reversible reaction (in most cases), but there is also an irreversible hydrolysis (it proceeds to the end, there will be no starting substance in the solution). Hydrolysis is an endothermic process (with an increase in temperature, both the rate of hydrolysis and the yield of hydrolysis products increase).

As can be seen from the definition that hydrolysis is an exchange reaction, it can be assumed that an OH group goes to the metal (+ a possible acid residue if a basic salt is formed (during the hydrolysis of a salt formed by a strong acid and a weak polyacid base)), and to the acid residue there is a hydrogen proton H + (+ a possible metal ion and a hydrogen ion, with the formation acid salt, if a salt formed by a weak polybasic acid is hydrolyzed)).

There are 4 types of hydrolysis:

1. Salt formed by a strong base and a strong acid. Since it has already been mentioned above, hydrolysis is an ion exchange reaction, and it proceeds only in the case of the formation of a weak electrolyte. As described above, an OH group goes to the metal, and a hydrogen proton H + goes to the acid residue, but neither a strong base nor a strong acid are weak electrolytes, therefore hydrolysis does not occur in this case:

NaCl+HOH≠NaOH+HCl

Medium reaction is close to neutral: pH≈7

2. Salt is formed by a weak base and a strong acid. As stated above: an OH group goes to the metal, and a hydrogen proton H + goes to the acidic residue. For example:

NH4Cl+HOH↔NH4OH+HCl

NH 4 + +Cl - +HOH↔NH 4 OH+H + +Cl -

NH 4 + +HOH↔NH 4 OH+H +

As can be seen from the example, hydrolysis proceeds along the cation, the reaction of the medium is acidic pH < 7.При написании уравнений гидролиза для солей, образованных сильной кислотой и слабым многокислотным основанием, то в правой части следует писать основную соль, так как гидролиз идёт только по первой ступени:

FeCl 2 + HOH ↔ FeOHCl + HCl

Fe 2+ +2Cl - +HOH↔FeO + +H + +2Cl -

Fe 2+ + HOH ↔ FeOH + + H +

3. The salt is formed by a weak acid and a strong base. As mentioned above: an OH group goes to the metal, and a hydrogen proton H + goes to the acid residue. For example:

CH 3 COONa+HOH↔NaOH+CH 3 COOH

СH 3 COO - +Na + +HOH↔Na + +CH 3 COOH+OH -

СH 3 COO - +HOH↔+CH 3 COOH+OH -

Hydrolysis proceeds along the anion, the reaction of the medium is alkaline, pH > 7. When writing the equations for the hydrolysis of a salt formed by a weak polybasic acid and a strong base, the formation of an acid salt should be written on the right side, hydrolysis proceeds in 1 step. For example:

Na 2 CO 3 + HOH ↔ NaOH + NaHCO 3

2Na + +CO 3 2- +HOH↔HCO 3 - +2Na + +OH -

CO 3 2- +HOH↔HCO 3 - +OH -

4. Salt is formed by a weak base and a weak acid. This is the only case when hydrolysis goes to the end, is irreversible (until the initial salt is completely consumed). For example:

CH 3 COONH 4 +HOH↔NH 4 OH+CH 3 COOH

This is the only case when hydrolysis goes to the end. Hydrolysis occurs both in the anion and in the cation; it is difficult to predict the reaction of the medium, but it is close to neutral: pH ≈ 7.

There is also a hydrolysis constant, consider it using the example of an acetate ion, denoting it Ac- . As can be seen from the examples above, acetic (ethanoic) acid is a weak acid, and, therefore, its salts are hydrolyzed according to the scheme:

Ac - +HOH↔HAc+OH -

Let's find the equilibrium constant for this system:

Knowing ionic product of water, we can express the concentration through it [ OH] - ,

Substituting this expression into the equation for the hydrolysis constant, we get:

Substituting the water ionization constant into the equation, we get:

But the constant dissociation of the acid (on the example of hydrochloric acid) is equal to:

Where is a hydrated hydrogen proton: . Similarly for acetic acid, as in the example. Substituting the value for the acid dissociation constant into the hydrolysis constant equation, we get:

As follows from the example, if the salt is formed by a weak base, then the denominator will contain the dissociation constant of the base, calculated on the same basis as the dissociation constant of the acid. If the salt is formed by a weak base and a weak acid, then the denominator will be the product of the dissociation constants of the acid and the base.

degree of hydrolysis.

There is also another value that characterizes hydrolysis - the degree of hydrolysis -α. Which is equal to the ratio of the amount (concentration) of salt undergoing hydrolysis to the total amount (concentration) of dissolved saltThe degree of hydrolysis depends on the concentration of salt, the temperature of the solution. It increases with dilution of the salt solution and with an increase in the temperature of the solution. Recall that the more dilute the solution, the lower the molar concentration of the original salt; and the degree of hydrolysis increases with increasing temperature, since hydrolysis is an endothermic process, as mentioned above.

The degree of salt hydrolysis is the higher, the weaker the acid or base that forms it. As follows from the equation for the degree of hydrolysis and types of hydrolysis: with irreversible hydrolysisα≈1.

The degree of hydrolysis and the hydrolysis constant are interconnected through the Ostwald equation (Wilhelm Friedrich Ostwald-sdilution akon Ostwald, bred in 1888year).The dilution law shows that the degree of electrolyte dissociation depends on its concentration and dissociation constant. Let us take the initial concentration of the substance asC 0 , and the dissociated part of the substance - forγ, recall the scheme of dissociation of a substance in solution:

AB↔A + +B -

Then Ostwald's law can be expressed as follows:

Recall that the equation contains concentrations at the moment of equilibrium. But if the substance is slightly dissociated, then (1-γ) → 1, which brings the Ostwald equation into the form: K d \u003d γ 2 C 0.

The degree of hydrolysis is similarly related to its constant:

In the vast majority of cases, this formula is used. But if necessary, you can express the degree of hydrolysis through the following formula:

Special cases of hydrolysis:

1) Hydrolysis of hydrides (compounds of hydrogen with elements (here we will consider only metals of groups 1 and 2 and metam), where hydrogen exhibits an oxidation state of -1):

NaH+HOH→NaOH+H 2

CaH 2 + 2HOH → Ca (OH) 2 + 2H 2

CH 4 +HOH→CO+3H 2

The reaction with methane is one of industrial ways obtaining hydrogen.

2) Hydrolysis of peroxides.Alkaline peroxides and alkaline earth metals decomposed by water, with the formation of the corresponding hydroxide and hydrogen peroxide (or oxygen):

Na 2 O 2 +2 H 2 O → 2 NaOH + H 2 O 2

Na 2 O 2 + 2H 2 O → 2NaOH + O 2

3) Hydrolysis of nitrides.

Ca 3 N 2 + 6HOH → 3Ca (OH) 2 + 2NH 3

4) Hydrolysis of phosphides.

K 3 P+3HOH→3KOH+PH 3

escaping gas PH 3 -phosphine, very poisonous, striking nervous system. It is also capable of spontaneous combustion upon contact with oxygen. Have you ever walked through a swamp at night or walked past cemeteries? We saw rare bursts of lights - "wandering lights", appear as phosphine burns.

5) Hydrolysis of carbides. Here are two reactions having practical use, since with their help 1 members of the homologous series of alkanes (reaction 1) and alkynes (reaction 2) are obtained:

Al 4 C 3 +12 HOH →4 Al (OH) 3 +3CH 4 (reaction 1)

CaC 2 +2 HOH →Ca(OH) 2 +2C 2 H 2 (reaction 2, the product is acylene, according to UPA With ethyn)

6) Hydrolysis of silicides. As a result of this reaction, 1 representative of the homologous series of silanes is formed (there are 8 in total) SiH 4 is a monomeric covalent hydride.

Mg 2 Si + 4HOH → 2Mg (OH) 2 + SiH 4

7) Hydrolysis of phosphorus halides. Phosphorus chlorides 3 and 5, which are acid chlorides of phosphorous and phosphoric acids, respectively, will be considered here:

PCl 3 + 3H 2 O \u003d H 3 PO 3 + 3HCl

PCl 5 + 4H 2 O \u003d H 3 PO 4 + 5HCl

8) Hydrolysis of organic substances. Fats are hydrolyzed, with the formation of glycerol (C 3 H 5 (OH) 3) and carboxylic acid (an example of limiting carboxylic acid) (C n H (2n + 1) COOH)

Esters:

CH 3 COOCH 3 + H 2 O↔CH 3 COOH + CH 3 OH

Alcohol:

C 2 H 5 ONa+H 2 O↔C 2 H 5 OH+NaOH

Living organisms carry out the hydrolysis of various organic substances in the course of reactions catabolism with the participation enzymes. For example, during hydrolysis with the participation of digestive enzymes proteins are broken down into amino acids, fats into glycerol and fatty acids, polysaccharides into monosaccharides (for example, into glucose).

When fats are hydrolyzed in the presence of alkalis, soap; hydrolysis of fats in the presence catalysts applied to obtain glycine and fatty acids.

Tasks

1) The degree of dissociation a of acetic acid in a 0.1 M solution at 18 ° C is 1.4 10 -2. Calculate the acid dissociation constant K d. (Hint - use the Ostwald equation.)

2) What mass of calcium hydride must be dissolved in water in order to reduce the released gas to iron 6.96 g of iron oxide ( II, III)?

3) Write the equation for the reaction Fe 2 (SO 4) 3 + Na 2 CO 3 + H 2 O

4) Calculate the degree, the constant of the hydrolysis of the Na 2 SO 3 salt for the concentration Cm = 0.03 M, taking into account only the 1st stage of hydrolysis. (The dissociation constant of sulfurous acid is taken equal to 6.3∙10 -8)

Solutions:

a) Substitute these problems into the Ostwald dilution law:

b) K d \u003d [C] \u003d (1.4 10 -2) 0.1 / (1 - 0.014) \u003d 1.99 10 -5

Answer. K d \u003d 1.99 10 -5.

c) Fe 3 O 4 + 4H 2 → 4H 2 O + 3Fe

CaH 2 +HOH→Ca(OH) 2 +2H 2

We find the number of moles of iron oxide (II, III), it is equal to the ratio of the mass of a given substance to its molar mass, we get 0.03 (mol). According to the UCR, we find that the moles of calcium hydride are 0.06 (mol). So the mass of calcium hydride is 2.52 (grams).

Answer: 2.52(grams).

d) Fe 2 (SO 4) 3 + 3Na 2 CO 3 + 3H 2 O → 3СO2 + 2Fe (OH) 3 ↓ + 3Na 2 SO 4

e) Sodium sulfite undergoes anion hydrolysis, the reaction of the salt solution medium is alkaline (pH > 7):
SO 3 2- + H 2 O<-->OH - + HSO 3 -
The hydrolysis constant (see equation above) is: 10 -14 / 6.3 * 10 -8 \u003d 1.58 * 10 -7
The degree of hydrolysis is calculated by the formula α 2 /(1 - α) = K h /C 0 .
So, α \u003d (K h / C 0) 1/2 \u003d (1.58 * 10 -7 / 0.03) 1/2 \u003d 2.3 * 10 -3

Answer: K h \u003d 1.58 * 10 -7; α \u003d 2.3 * 10 -3

Editor: Kharlamova Galina Nikolaevna

one). Hydrolysis is an endothermic reaction, so an increase in temperature enhances hydrolysis.

2). An increase in the concentration of hydrogen ions weakens the hydrolysis, in the case of hydrolysis by the cation. Similarly, increasing the concentration of hydroxide ions weakens the hydrolysis, in the case of anion hydrolysis.

3). When diluted with water, the equilibrium shifts in the direction of the reaction, i.e. to the right, the degree of hydrolysis increases.

4). Additives of foreign substances can affect the equilibrium position when these substances react with one of the participants in the reaction. So, when copper sulfate is added to a solution

2CuSO4 + 2H2O<=>(CuOH)2SO4 + H2SO4

sodium hydroxide solution, the hydroxide ions contained in it will interact with hydrogen ions. As a result, their concentration will decrease, and, according to Le Chatelier's principle, the equilibrium in the system will shift to the right, the degree of hydrolysis will increase. And if a solution of sodium sulfide is added to the same solution, then the equilibrium will not shift to the right, as one might expect (mutual enhancement of hydrolysis), but, on the contrary, to the left, due to the binding of copper ions into practically insoluble copper sulfide.

5). salt concentration. Consideration of this factor leads to a paradoxical conclusion: the equilibrium in the system shifts to the right, in accordance with Le Chatelier's principle, but the degree of hydrolysis decreases.

Example,

Al(NO 3 ) 3

The salt is hydrolyzed at the cation. It is possible to enhance the hydrolysis of this salt if:

heat or dilute the solution with water;
add a solution of alkali (NaOH);
add a solution of salt hydrolyzed by the anion Na 2 CO 3 ;

The hydrolysis of this salt can be weakened if:

lead dissolution in the cold;
prepare the most concentrated solution of Al(NO 3 ) 3 as possible;
add an acid to the solution, such as HCl

Hydrolysis of salts of polyacid bases and polybasic acids proceeds stepwise

For example, the hydrolysis of iron (II) chloride includes two steps:

1st step

FeCl 2 + HOH<=>Fe(OH)Cl + HCl
Fe2+ + 2Cl - + H + + OH -<=>Fe(OH) + + 2Cl - + H +

2nd stage

Fe(OH)Cl + HOH<=>Fe(OH) 2 + HCl
Fe(OH) + + Cl - + H + + OH -<=>Fe( OH) 2 + H + + Cl -

The hydrolysis of sodium carbonate includes two steps:

1st step

Na 2 CO 3 + HOH<=>NaHCO 3 + NaOH
CO 3 2- + 2Na + + H + + OH - => HCO 3 - + OH - + 2Na +

2nd stage

NaHCO 3 + H 2 O<=>NaOH + H 2 CO 3
HCO 3 - + Na + + H + + OH -<=>H 2 CO 3 + OH - + Na +

Hydrolysis is a reversible process. An increase in the concentration of hydrogen ions and hydroxide ions prevents the reaction from proceeding to completion. In parallel with hydrolysis, a neutralization reaction takes place when the resulting weak base (Fe (OH) 2) interacts with a strong acid, and the resulting weak acid (H 2 CO 3) reacts with an alkali.

Hydrolysis proceeds irreversibly if an insoluble base and (or) a volatile acid is formed as a result of the reaction:

Al 2 S 3 + 6H 2 O \u003d\u003e 2Al (OH) 3 ↓ + 3H 2 S

Salts completely decomposed by water - Al2S3 , cannot be obtained by the exchange reaction in aqueous solutions, since instead of the exchange, the reaction of joint hydrolysis proceeds:

2AlCl 3 +3Na 2 S≠Al 2 S 3 +6NaCl

2AlCl 3 +3Na 2 S+6H 2 O=2Al(OH) 3 ↓+6NaCl+3H 2 S(mutual enhancement of hydrolysis)

Therefore, they are obtained in anhydrous media by sintering or other methods, for example:

2Al+3S = t°C\u003d Al 2 S 3

Examples of hydrolysis reactions

(NH 4) 2 CO 3 ammonium carbonate salt, weak acid and weak base. Soluble. Hydrolyzes both cation and anion at the same time. The number of steps is 2.

Stage 1: (NH 4) 2 CO 3 + H 2 O ↔ NH 4 OH + NH 4 HCO 3

2 step: NH 4 HCO 3 + H 2 O ↔NH 4 OH + H 2 CO 3

The reaction of the solution is slightly alkaline pH > 7, because ammonium hydroxide is a stronger electrolyte than carbonic acid. K d (NH 4 OH)> K d (H 2 CO 3)

CH 3 COONH 4 ammonium acetate salt, weak acid and weak base. Soluble. Hydrolyzes both cation and anion at the same time. The number of steps is 1.

CH 3 COONH 4 + H 2 O ↔NH 4 OH + CH 3 COOH

The reaction of the solution is neutral pH \u003d 7, because K d (CH 3 COO H) \u003d K d (NH 4 OH)

K2HPO4– potassium hydrogen phosphate salt, weak acid and strong base. Soluble. Hydrolyzed at the anion. The number of steps is 2.

1 step: K 2 HPO 4 +H 2 O ↔KH 2 PO 4 +KOH

2 step: KH 2 PO 4 +H 2 O ↔H 3 PO 4 +KOH

solution reaction 1 step slightly alkalinepH=8,9 , since as a result of hydrolysis, OH - ions accumulate in the solution and the hydrolysis process prevails over the process of dissociation of HPO 4 2- ions, giving H + ions (HPO 4 2- ↔H + + PO 4 3-)

solution reaction 2 stages slightly acidicpH=6,4 , since the process of dissociation of dihydroorthophosphate ions prevails over the process of hydrolysis, while hydrogen ions not only neutralize hydroxide ions, but also remain in excess, which causes a weakly acid reaction of the medium.

Task: Determine the medium of sodium bicarbonate and sodium hydrosulfite solutions.

Decision:

1) Consider the processes in a solution of sodium bicarbonate. The dissociation of this salt proceeds in two stages, hydrogen cations are formed in the second stage:

NaHCO 3 \u003d Na + + HCO 3 - (I)

HCO 3 - ↔ H + + CO 3 2- ( II )

The dissociation constant for the second stage is K 2 of carbonic acid, equal to 4.8∙10 -11.

The hydrolysis of sodium bicarbonate is described by the equation:

NaHCO 3 + H 2 O ↔ H 2 CO 3 + NaOH

HCO 3 - + H 2 O ↔H 2 CO 3 + OH -, whose constant is

K g \u003d K w / K 1 (H 2 CO 3) \u003d 1 ∙ 10 -14 / 4.5 ∙ 10 -7 \u003d 2.2 ∙ 10 -8.

The hydrolysis constant is noticeably larger than the dissociation constant, therefore solutionNaHCO 3 has an alkaline environment.

2) Consider the processes in a solution of sodium hydrosulfite. The dissociation of this salt proceeds in two stages, hydrogen cations are formed in the second stage:

NaHSO 3 \u003d Na + + HSO 3 - (I)

HSO 3 - ↔ H + + SO 3 2- (II)

The dissociation constant for the second stage is K 2 of sulfurous acid, equal to 6.2∙10 -8.

The hydrolysis of sodium hydrosulfite is described by the equation:

NaHSO 3 + H 2 O ↔H 2 SO 3 + NaOH

HSO 3 - + H 2 O ↔H 2 SO 3 + OH -, whose constant is

K g \u003d K w / K 1 (H 2 SO 3) \u003d 1 ∙ 10 -14 / 1.7 ∙ 10 -2 \u003d 5.9 ∙ 10 -13.

In this case, the dissociation constant is greater than the hydrolysis constant, so solution

NaHSO 3 has an acidic environment.

Task: Determine the medium of the ammonium cyanide salt solution.

Decision:

NH 4 CN ↔NH 4 + + CN -

NH 4 + + 2H 2 O ↔NH 3. H 2 O + H 3 O +

CN - + H 2 O ↔HCN + OH -

NH 4 CN + H 2 O↔ NH 4 OH + HCN

K d (HCN) =7.2∙10 -10; K d (NH 4 OH) \u003d 1.8 ∙ 10 -5

Answer: Hydrolysis by cation and anion, because K o > K k, slightly alkaline, pH > 7

hydrolysis
called
reactions
exchange
interactions
substances with water, leading to their
decomposition.

Peculiarities

Hydrolysis of organic
substances
Living organisms carry out
hydrolysis of various organic
substances during reactions
the participation of enzymes.
For example, during hydrolysis
participation of digestive
enzymes PROTEINS are broken down
for AMINO ACIDS,
FATS - to GLYCERIN and
FATTY ACID,
POLYSACCHARIDES (eg.
starch and cellulose)
MONOSACCHARIDES (eg.
GLUCOSE), NUCLEIC
ACIDS - for free
NUCLEOTIDES.
During the hydrolysis of fats
the presence of alkalis
receive soap; hydrolysis
fat in the presence
catalysts used
for glycerin and
fatty acids. hydrolysis
wood get ethanol, and
peat hydrolysis products
find application in
fodder production
yeast, wax, fertilizers and
others

Hydrolysis of organic compounds

fats are hydrolyzed to form glycerol and
carboxylic acids (with NaOH - saponification).
starch and cellulose are hydrolyzed to
glucose:

Reversible and irreversible hydrolysis

Almost all hydrolysis reactions
organic matter
reversible. But there is also
irreversible hydrolysis.
General property irreversible
hydrolysis - one (preferably both)
from hydrolysis products
be removed from the sphere of reaction
as:
- DRAINAGE,
- GAS.
CaC₂ + 2H₂O = Ca(OH)₂↓ + C₂H₂
In the hydrolysis of salts:
Al₄C₃ + 12 H₂O = 4 Al(OH)₃↓ + 3CH₄
Al₂S₃ + 6 H₂O = 2 Al(OH)₃↓ + 3 H₂S
CaH₂ + 2 H₂O = 2Ca(OH)₂↓ + H₂

H I D R O L I S S O L E Y

HYDROLYSIS OF SALT
Salt hydrolysis -
kind of reactions
hydrolysis due to
reactions
ion exchange in solutions
(water) soluble
electrolyte salts.
The driving force behind the process
is the interaction
ions with water, leading to
weak
electrolyte in ionic or
molecular form
("binding of ions").
Distinguish between reversible and
irreversible hydrolysis of salts.
1. Hydrolysis of weak salt
acid and strong base
(hydrolysis by anion).
2. Hydrolysis of strong salt
acid and weak base
(hydrolysis by cation).
3. Hydrolysis of weak salt
acid and weak base
(irreversible).
Salt of a strong acid and
no strong foundation
undergoes hydrolysis.

Reaction equations

Hydrolysis of a salt of a weak acid and a strong base
(hydrolysis by anion):
(the solution has an alkaline environment, the reaction proceeds
reversibly, hydrolysis in the second stage proceeds in
negligible degree).
Hydrolysis of a salt of a strong acid and a weak base
(hydrolysis by cation):
(the solution is acidic, the reaction proceeds reversibly,
hydrolysis in the second stage proceeds in negligible
degrees).

10.

Hydrolysis of a salt of a weak acid and a weak base:
(the equilibrium is shifted towards products, hydrolysis
proceeds almost completely, since both products
reactions leave the reaction zone in the form of a precipitate or
gas).
Salt of a strong acid and a strong base
undergoes hydrolysis and the solution is neutral.

11. SCHEME OF SODIUM CARBONATE HYDROLYSIS

Na₂CO₃
NaOH
strong base
H₂CO₃
weak acid
ALKALINE ENVIRONMENT
SALT ACID, hydrolysis by
ANION

12. SCHEME OF HYDROLYSIS OF COPPER(II) CHLORIDE

CuCl₂
Cu(OH)₂↓
weak base
HCl
strong acid
ACID ENVIRONMENT
BASIC SALT, hydrolysis according to
CATION

13. ALUMINUM SULFIDE HYDROLYSIS SCHEME

Al₂S₃
Al(OH)₃↓
weak base
H₂S
weak acid
NEUTRAL REACTION
ENVIRONMENTS
hydrolysis irreversible

14.

ROLE OF HYDROLYSIS IN NATURE
transformation earth's crust
Ensuring a slightly alkaline marine environment
water
ROLE OF HYDROLYSIS IN LIFE
HUMAN
Wash
washing dishes
Washing with soap
Digestion processes

transcript

1 HYDROLYSIS OF ORGANIC AND INORGANIC SUBSTANCES

2 Hydrolysis (from the ancient Greek "ὕδωρ" water and "λύσις" decomposition) one of the types chemical reactions, where, when substances interact with water, the initial substance decomposes with the formation of new compounds. The mechanism of hydrolysis of compounds various classes: - salts, carbohydrates, fats, esters, etc. have significant differences

3 Hydrolysis of organic substances Living organisms carry out the hydrolysis of various organic substances in the course of reactions with the participation of ENZYMES. For example, during hydrolysis, with the participation of digestive enzymes, PROTEINS are broken down into AMINO ACIDS, FATS into GLYCEROL and FATTY ACIDS, POLYSACCHARIDES (for example, starch and cellulose) into MONOSACCHARIDES (for example, into GLUCOSE), NUCLEIC ACIDS into free NUCLEOTIDES. When fats are hydrolyzed in the presence of alkalis, soap is obtained; hydrolysis of fats in the presence of catalysts is used to obtain glycerol and fatty acids. Ethanol is obtained by hydrolysis of wood, and peat hydrolysis products are used in the production of fodder yeast, wax, fertilizers, etc.

4 1. Hydrolysis of organic compounds fats are hydrolyzed to obtain glycerol and carboxylic acids (saponification with NaOH):

5 starch and cellulose are hydrolyzed to glucose:

7 TEST 1. During the hydrolysis of fats, 1) alcohols and mineral acids 2) aldehydes and carboxylic acids 3) monohydric alcohols and carboxylic acids 4) glycerol and carboxylic acids ANSWER: 4 2. Hydrolysis undergoes: 1) Acetylene 2) Cellulose 3) Ethanol 4) Methane ANSWER: 2 3. Hydrolysis undergoes: 1) Glucose 2) Glycerin 3) Fat 4) Acetic acid ANSWER: 3

8 4. During the hydrolysis of esters, the following are formed: 1) Alcohols and aldehydes 2) carboxylic acids and glucose 3) Starch and glucose 4) Alcohols and carboxylic acids ANSWER: 4 5. Starch hydrolysis produces: 1) Sucrose 2) Fructose 3) Maltose 4) Glucose ANSWER: 4

9 2. Reversible and irreversible hydrolysis Almost all the considered reactions of hydrolysis of organic substances are reversible. But there is also irreversible hydrolysis. The general property of irreversible hydrolysis is that one (preferably both) of the hydrolysis products must be removed from the reaction sphere in the form of: - SEDIMENT, - GAS. CaC₂ + 2H₂O = Ca(OH)₂ + C₂H₂ During the hydrolysis of salts: Al₄C₃ + 12 H₂O = 4 Al(OH)₃ + 3CH₄ Al₂S₃ + 6 H₂O CaH₂ + 2 H₂O = 2 Al(OH)₃ + 3 H₂S = 2Ca(OH )₂ + H₂

10 HYDROLYSIS SOLEY Hydrolysis of salts is a kind of hydrolysis reactions caused by the occurrence of ion exchange reactions in solutions of (aqueous) soluble electrolyte salts. The driving force of the process is the interaction of ions with water, leading to the formation of a weak electrolyte in ionic or molecular form (“ion binding”). Distinguish between reversible and irreversible hydrolysis of salts. 1. Hydrolysis of a salt of a weak acid and a strong base (anion hydrolysis). 2. Hydrolysis of a salt of a strong acid and a weak base (cation hydrolysis). 3. Hydrolysis of the salt of a weak acid and a weak base (irreversible) The salt of a strong acid and a strong base does not undergo hydrolysis

12 1. Hydrolysis of a salt of a weak acid and a strong base (anion hydrolysis): (solution has an alkaline environment, the reaction is reversible, hydrolysis in the second stage proceeds to an insignificant degree) 2. Hydrolysis of a salt of a strong acid and a weak base (cation hydrolysis): (the solution has an acidic environment, the reaction proceeds reversibly, hydrolysis in the second stage proceeds to an insignificant degree)

13 3. Hydrolysis of a salt of a weak acid and a weak base: (the equilibrium is shifted towards the products, the hydrolysis proceeds almost completely, since both reaction products leave the reaction zone in the form of a precipitate or gas). The salt of a strong acid and a strong base does not undergo hydrolysis and the solution is neutral.

14 SCHEME OF SODIUM CARBONATE HYDROLYSIS NaOH strong base Na₂CO₃ H₂CO₃ weak acid > [H]+ BASIC MEDIUM ACID SALT, ANION hydrolysis

15 First hydrolysis stage Na₂CO₃ + H₂O NaOH + NaHCO₃ 2Na+ + CO₃ ² + H₂O Na+ + OH + Na+ + HCO₃ CO₃ ² + H₂O OH + HCO₃ Second hydrolysis stage NaHCO₃ + H₂O = NaOH + H₂CO ₃ CO₂ H₂O Na+ + HCO + OH + CO₂ + H₂O HCO₃ + H₂O = OH + CO₂ + H₂O

16 COPPER(II) CHLORIDE HYDROLYSIS SCHEME Cu(OH)₂ weak base CuCl₂ HCl strong acid< [ H ]+ КИСЛАЯ СРЕДА СОЛЬ ОСНОВНАЯ, гидролиз по КАТИОНУ

17 First stage of hydrolysis CuCl₂ + H₂O (CuOH)Cl + HCl Cu+² + 2 Cl + H₂O (CuOH)+ + Cl + H+ + Cl Cu+² + H₂O (CuOH)+ + H+ Second stage of hydrolysis (СuOH)Cl + H₂O Cu(OH)₂ + HCl (Cu OH)+ + Cl + H₂O Cu(OH)₂ + H+ + Cl (CuOH)+ + H₂O Cu(OH)₂ + H+

18 ALUMINUM SULFIDE HYDROLYSIS SCHEME Al₂S₃ Al(OH)₃ H₂S weak base weak acid = [H]+ NEUTRAL REACTION OF THE MEDIUM irreversible hydrolysis

19 Al₂S₃ + 6 H₂O = 2Al(OH)₃ + 3H₂S HYDROLYSIS OF SODIUM CHLORIDE NaCl NaOH HCl strong base strong acid = [H]+ NEUTRAL REACTION OF THE ENVIRONMENT no hydrolysis occurs NaCl + H₂O = NaOH + HCl Na+ + Cl + H₂O = Na+ + OH + H+ + Cl

20 Transformation of the earth's crust Providing a slightly alkaline environment for sea water THE ROLE OF HYDROLYSIS IN HUMAN LIFE Laundry Washing dishes Washing with soap Digestion processes

21 Write the hydrolysis equations: A) K₂S B) FeCl₂ C) (NH₄)₂S D) BaI₂ K₂S: KOH is a strong base H₂S weak acid HS + K+ + OH S² + H₂O HS + OH FeCl₂ : Fe(OH)₂ - weak base HCL - strong acid FeOH)+ + Cl + H+ + Cl Fe +² + H₂O (FeOH)+ + H+

22 (NH₄)₂S: NH₄OH - weak base; H₂S - weak acid HI - strong acid HYDROLYSIS NO

23 Perform on a sheet of paper. Hand in your work to the teacher at the next lesson.

25 7. An aqueous solution of which of the salts has a neutral environment? a) Al(NO₃)₃ b) ZnCl₂ c) BaCl₂ d) Fe(NO₃)₂ 8. In which solution will the color of litmus be blue? a) Fe₂(SO₄)₃ b) K₂S c) CuCl₂ d) (NH₄)₂SO₄

26 9. 1) potassium carbonate 2) ethane 3) zinc chloride 4) fat 10. During the hydrolysis of fiber (starch), the following can be formed: 1) glucose 2) only sucrose 3) only fructose 4) carbon dioxide and water 11. The solution medium as a result of the hydrolysis of sodium carbonate 1) alkaline 2) strongly acidic 3) acidic 4) neutral 12. Hydrolysis undergoes 1) CH 3 COOK 2) KCI 3) CaCO 3 4) Na 2 SO 4

27 13. Hydrolysis is not subjected to 1) iron sulfate 2) alcohols 3) ammonium chloride 4) esters

28 PROBLEM Explain why when pouring solutions - FeCl₃ and Na₂CO₃ - precipitates and gas is released? 2FeCl₃ + 3Na₂CO₃ + 3H₂O = 2Fe(OH)₃ + 6NaCl + 3CO₂

29 Fe+³ + H₂O (FeOH)+² + H+ CO₃ ² + H₂O HCO₃ + OH CO₂ + H₂O Fe(OH)₃

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