The process of formation of weakly dissociated compounds with a change in the hydrogen index of the medium during the interaction of water and salt is called hydrolysis.
Hydrolysis of salts occurs when one water ion binds to form sparingly soluble or weakly dissociated compounds due to a shift in the dissociation equilibrium. For the most part, this process is reversible and is enhanced by dilution or increased temperature.
To find out which salts undergo hydrolysis, you need to know what strength bases and acids were used in its formation. There are several types of their interactions.
Obtaining a salt from a base and a weak acid
Examples include aluminum and chromium sulfide, as well as ammonium acetate and ammonium carbonate. These salts, when dissolved in water, form bases and weakly dissociating acids. To trace the reversibility of the process, it is necessary to create an equation for the reaction of salt hydrolysis:
Ammonium acetate + water ↔ ammonia + acetic acid
In ionic form, the process looks like:
CH 3 COO- + NH 4 + + H 2 O ↔ CH 3 COOH + NH 4 OH.
In the above hydrolysis reaction, ammonia and acetic acid are formed, that is, weakly dissociating substances.
The hydrogen index of aqueous solutions (pH) directly depends on the relative strength, that is, the dissociation constants of the reaction products. The above reaction will be slightly alkaline, since the decomposition constant of acetic acid is less than the constant of ammonium hydroxide, that is, 1.75 ∙ 10 -5 is less than 6.3 ∙ 10 -5. If bases and acids are removed from solution, then the process is completed.
Consider an example of irreversible hydrolysis:
Aluminum sulfate + water = aluminum hydroxide + hydrogen sulfide
In this case, the process is irreversible, because one of the reaction products is removed, that is, precipitates.
Hydrolysis of compounds obtained by reacting a weak base with a strong acid
This type of hydrolysis describes the decomposition reactions of aluminum sulfate, copper chloride or bromide, and ferric or ammonium chloride. Consider the reaction of ferric chloride, which occurs in two stages:
Stage one:
Ferric chloride + water ↔ ferric hydroxychloride + hydrochloric acid
The ionic equation for the hydrolysis of ferric chloride salts takes the form:
Fe 2+ + H 2 O + 2Cl - ↔ Fe(OH) + + H + + 2Cl -
Second stage of hydrolysis:
Fe(OH)+ + H 2 O + Cl - ↔ Fe(OH) 2 + H + + Cl -
Due to the deficiency of hydroxo group ions and the accumulation of hydrogen ions, the hydrolysis of FeCl 2 proceeds in the first stage. A strong hydrochloric acid and a weak base, iron hydroxide, are formed. In the case of such reactions, the medium turns out to be acidic.
Non-hydrolysing salts obtained by reacting strong bases and acids
Examples of such salts include calcium or sodium chlorides, potassium sulfate and rubidium bromide. However, these substances do not hydrolyze, since when dissolved in water they have a neutral environment. The only low-dissociating substance in this case is water. To confirm this statement, you can create an equation for the hydrolysis of sodium chloride salts with the formation of hydrochloric acid and sodium hydroxide:
NaCl + H 2 O ↔ NaOH + HCl
Reaction in ionic form:
Na + + Cl - + H 2 O↔ Na + + OH - + H + + Cl -
H 2 O ↔ H + + OH -
Salts as a product of the reaction of a strong alkali and a weak acid
In this case, the hydrolysis of salts occurs through the anion, which corresponds to an alkaline pH value. Examples include sodium acetate, sodium sulfate and carbonate, potassium silicate and sulfate, and sodium hydrocyanic acid. For example, let’s create ionic-molecular equations for the hydrolysis of sodium sulfide and sodium acetate salts:
Dissociation of sodium sulfide:
Na 2 S ↔ 2Na + + S 2-
The first stage of hydrolysis of a polybasic salt occurs at the cation:
Na 2 S + H 2 O ↔ NaH S + NaOH
Notation in ionic form:
S 2- + H 2 O ↔ HS - + OH -
The second step is feasible if the reaction temperature is increased:
HS - + H 2 O ↔ H 2 S + OH -
Let's consider another hydrolysis reaction using sodium acetate as an example:
Sodium acetate + water ↔ acetic acid + caustic soda.
In ionic form:
CH 3 COO - + H 2 O ↔ CH 3 COOH + OH -
As a result of the reaction, weak acetic acid is formed. In both cases the reactions will be alkaline.
Reaction equilibrium according to Le Chatelier's principle
Hydrolysis, like other chemical reactions, can be reversible or irreversible. In the case of reversible reactions, one of the reagents is not completely consumed, while irreversible processes occur with complete consumption of the substance. This is due to a shift in the equilibrium of reactions, which is based on changes in physical characteristics such as pressure, temperature and mass fraction of reagents.
According to the concept of Le Chatelier's principle, the system will be considered equilibrium until one or more external conditions of the process are changed. For example, when the concentration of one of the substances decreases, the equilibrium of the system will gradually begin to shift towards the formation of the same reagent. Hydrolysis of salts also has the ability to obey Le Chatelier’s principle, with the help of which the process can be weakened or strengthened.
Increased hydrolysis
Hydrolysis can be enhanced to the point of complete irreversibility in several ways:
- Increase the rate of formation of OH - and H + ions. To do this, the solution is heated, and due to the increase in heat absorption by water, that is, endothermic dissociation, this indicator increases.
- Add water.
- Convert one of the products into a gaseous state or bind into a heavily soluble substance.
Hydrolysis suppression
The hydrolysis process can be suppressed, as well as enhanced, in several ways.
Add one of the substances formed in the process into the solution. For example, to alkalize the solution if the pH is 7, or, on the contrary, to acidify it, where the reaction medium is less than 7 in pH.
Mutual enhancement of hydrolysis
Mutual enhancement of hydrolysis is applied if the system has become equilibrium. Let's look at a specific example where systems in different vessels have become equilibrium:
Al 3+ + H 2 O ↔ AlOH 2+ + H +
CO 3 2- + H 2 O ↔ NCO 3 - + OH -
Both systems are slightly hydrolyzed, therefore, if you mix them with each other, the binding of hydroxoins and hydrogen ions will occur. As a result, we obtain the molecular equation for the hydrolysis of salts:
Aluminum chloride + sodium carbonate + water = sodium chloride + aluminum hydroxide + carbon dioxide.
According to Le Chatelier's principle, the equilibrium of the system will move towards the reaction products, and hydrolysis will proceed to completion with the formation of aluminum hydroxide, which precipitates. Such an intensification of the process is possible only if one of the reactions proceeds through the anion, and the other through the cation.
Hydrolysis by anion
Hydrolysis of aqueous solutions of salts is carried out by combining their ions with water molecules. One of the methods of hydrolysis is carried out by anion, that is, the addition of an aqueous ion H +.
For the most part, salts that are formed through the interaction of a strong hydroxide and a weak acid are subject to this method of hydrolysis. An example of anion-decomposing salts is sodium sulfate or sulfite, as well as potassium carbonate or phosphate. The hydrogen index is more than seven. As an example, let's look at the dissociation of sodium acetate:
In solution, this compound is divided into a cation - Na +, and an anion - CH 3 COO -.
The dissociated sodium acetate cation, formed by a strong base, cannot react with water.
In this case, acid anions easily react with H 2 O molecules:
CH 3 COO - + HON = CH 3 COOH + OH -
Consequently, hydrolysis occurs at the anion, and the equation takes the form:
CH3COONa + HON = CH 3 COOH + NaOH
If polybasic acids undergo hydrolysis, the process occurs in several stages. Under normal conditions, such substances are hydrolyzed in the first stage.
Hydrolysis by cation
Cationic hydrolysis mainly affects salts formed by the interaction of a strong acid and a weak base. Examples include ammonium bromide, copper nitrate, and zinc chloride. In this case, the environment in the solution during hydrolysis corresponds to less than seven. Let's consider the process of hydrolysis by cation using aluminum chloride as an example:
In an aqueous solution, it dissociates into the anion - 3Cl - and the cation - Al 3+.
Strong hydrochloric acid ions do not react with water.
Ions (cations) of the base, on the contrary, are subject to hydrolysis:
Al 3+ + HOH = AlOH 2+ + H +
In molecular form, the hydrolysis of aluminum chloride is as follows:
AlCl3 + H 2 O = AlOHCl + HCl
Under normal conditions, it is preferable to neglect hydrolysis in the second and third stages.
Degree of dissociation
Any hydrolysis reaction of salts is characterized by the degree of dissociation, which shows the ratio between the total number of molecules and molecules capable of transitioning to an ionic state. The degree of dissociation is characterized by several indicators:
- Temperature at which hydrolysis occurs.
- Concentration of the dissociated solution.
- Origin of soluble salt.
- The nature of the solvent itself.
According to the degree of dissociation, all solutions are divided into strong and weak electrolytes, which, in turn, exhibit different degrees when dissolved in different solvents.
Dissociation constant
A quantitative indicator of the ability of a substance to decompose into ions is the dissociation constant, also called the equilibrium constant. In simple terms, the equilibrium constant is the ratio of electrolytes decomposed into ions to undissociated molecules.
Unlike the degree of dissociation, this parameter does not depend on external conditions and the concentration of the saline solution during the hydrolysis process. When polybasic acids dissociate, the degree of dissociation at each step becomes an order of magnitude less.
Indicator of acid-base properties of solutions
Hydrogen index or pH is a measure for determining the acid-base properties of a solution. Water dissociates into ions in limited quantities and is a weak electrolyte. When calculating the hydrogen index, a formula is used, which is the negative decimal logarithm of the accumulation of hydrogen ions in solutions:
pH = -log[H + ]
- For an alkaline environment, this figure will be more than seven. For example, [H + ] = 10 -8 mol/l, then pH = -log = 8, that is, pH ˃ 7.
- For an acidic environment, on the contrary, the pH value should be less than seven. For example, [H + ] = 10 -4 mol/l, then pH = -log = 4, that is, pH ˂ 7.
- For a neutral environment, pH = 7.
Very often, to determine the pH of solutions, an express method using indicators is used, which, depending on the pH, change their color. For a more accurate determination, ionomers and pH meters are used.
Quantitative characteristics of hydrolysis
Hydrolysis of salts, like any other chemical process, has a number of characteristics that make the process possible. The most significant quantitative characteristics include the constant and degree of hydrolysis. Let's take a closer look at each of them.
Degree of hydrolysis
To find out which salts undergo hydrolysis and in what quantity, a quantitative indicator is used - the degree of hydrolysis, which characterizes the completeness of hydrolysis. The degree of hydrolysis is the portion of a substance from the total number of molecules capable of hydrolysis, written as a percentage:
h = n/N∙ 100%,
where the degree of hydrolysis is h;
number of salt particles subjected to hydrolysis - n;
the total sum of salt molecules participating in the reaction is N.
Factors influencing the degree of hydrolysis include:
- constant hydrolysis;
- temperature, with an increase in which the degree increases due to increased interaction of ions;
- salt concentration in solution.
Hydrolysis constant
It is the second most important quantitative characteristic. In general, the equations for hydrolysis of salts can be written as:
MA + NON ↔ MON + NA
It follows that the equilibrium constant and the concentration of water in the same solution are constant quantities. Accordingly, the product of these two indicators will also be a constant value, which means the hydrolysis constant. In general, Kg can be written as:
Kg = ([NA]∙[MON])/[MA],
where HA is an acid,
MON - base.
In a physical sense, the hydrolysis constant describes the ability of a particular salt to undergo the process of hydrolysis. This parameter depends on the nature of the substance and its concentration.
We study the effect of a universal indicator on solutions of certain salts 
As we can see, the environment of the first solution is neutral (pH = 7), the second is acidic (pH< 7), третьего щелочная (рН >7). How can we explain such an interesting fact? 🙂
First, let's remember what pH is and what it depends on.
pH is a hydrogen index, a measure of the concentration of hydrogen ions in a solution (according to the first letters of the Latin words potentia hydrogeni - the strength of hydrogen).
pH is calculated as the negative decimal logarithm of the hydrogen ion concentration expressed in moles per liter:
In pure water at 25 °C, the concentrations of hydrogen ions and hydroxide ions are the same and amount to 10 -7 mol/l (pH = 7).
When the concentrations of both types of ions in a solution are equal, the solution is neutral. When > the solution is acidic, and when > it is alkaline.
What causes a violation of the equality of concentrations of hydrogen ions and hydroxide ions in some aqueous solutions of salts?
The fact is that there is a shift in the equilibrium of water dissociation due to the binding of one of its ions ( or ) with salt ions with the formation of a slightly dissociated, sparingly soluble or volatile product. This is the essence of hydrolysis.
- this is the chemical interaction of salt ions with water ions, leading to the formation of a weak electrolyte - an acid (or acid salt) or a base (or basic salt).
The word "hydrolysis" means decomposition by water ("hydro" - water, "lysis" - decomposition).
Depending on which salt ion interacts with water, three types of hydrolysis are distinguished:
- hydrolysis by cation (only the cation reacts with water);
- hydrolysis by anion (only the anion reacts with water);
- joint hydrolysis - hydrolysis at the cation and at the anion (both the cation and the anion react with water).
Any salt can be considered as a product formed by the interaction of a base and an acid:
Hydrolysis of a salt is the interaction of its ions with water, leading to the appearance of an acidic or alkaline environment, but not accompanied by the formation of precipitate or gas.
The hydrolysis process occurs only with the participation soluble salts and consists of two stages:
1)dissociation salts in solution - irreversible reaction (degree of dissociation, or 100%);
2) actually , i.e. interaction of salt ions with water, - reversible reaction (degree of hydrolysis ˂ 1, or 100%)
Equations of the 1st and 2nd stages - the first of them is irreversible, the second is reversible - you cannot add them!
Note that salts formed by cations alkalis and anions strong acids do not undergo hydrolysis; they only dissociate when dissolved in water. In solutions of salts KCl, NaNO 3, NaSO 4 and BaI, the medium neutral.
Hydrolysis by anion
In case of interaction anions dissolved salt with water the process is called hydrolysis of salt at anion.
1) KNO 2 = K + + NO 2 - (dissociation)
2) NO 2 - + H 2 O ↔ HNO 2 + OH - (hydrolysis)
The dissociation of the KNO 2 salt occurs completely, the hydrolysis of the NO 2 anion occurs to a very small extent (for a 0.1 M solution - by 0.0014%), but this is enough for the solution to become alkaline(among the products of hydrolysis there is an OH - ion), it contains p H = 8.14.
Anions undergo hydrolysis only weak acids (in this example, the nitrite ion NO 2, corresponding to the weak nitrous acid HNO 2). The anion of a weak acid attracts the hydrogen cation present in water and forms a molecule of this acid, while the hydroxide ion remains free:
NO 2 - + H 2 O (H +, OH -) ↔ HNO 2 + OH -
Examples:
a) NaClO = Na + + ClO -
ClO - + H 2 O ↔ HClO + OH -
b) LiCN = Li + + CN -
CN - + H 2 O ↔ HCN + OH -
c) Na 2 CO 3 = 2Na + + CO 3 2-
CO 3 2- + H 2 O ↔ HCO 3 — + OH —
d) K 3 PO 4 = 3K + + PO 4 3-
PO 4 3- + H 2 O ↔ HPO 4 2- + OH —
e) BaS = Ba 2+ + S 2-
S 2- + H 2 O ↔ HS — + OH —
Please note that in examples (c-e) you cannot increase the number of water molecules and instead of hydroanions (HCO 3, HPO 4, HS) write the formulas of the corresponding acids (H 2 CO 3, H 3 PO 4, H 2 S). Hydrolysis is a reversible reaction, and it cannot proceed “to the end” (until the formation of acid).
If such an unstable acid as H 2 CO 3 were formed in a solution of its salt NaCO 3, then the release of CO 2 gas from the solution would be observed (H 2 CO 3 = CO 2 + H 2 O). However, when soda is dissolved in water, a transparent solution is formed without gas evolution, which is evidence of the incompleteness of the hydrolysis of the anion with the appearance in the solution of only carbonic acid hydranions HCO 3 -.
The degree of hydrolysis of the salt by anion depends on the degree of dissociation of the hydrolysis product – the acid. The weaker the acid, the higher the degree of hydrolysis. For example, CO 3 2-, PO 4 3- and S 2- ions are hydrolyzed to a greater extent than the NO 2 ion, since the dissociation of H 2 CO 3 and H 2 S is in the 2nd stage, and H 3 PO 4 in The 3rd stage proceeds significantly less than the dissociation of the acid HNO 2. Therefore, solutions, for example, Na 2 CO 3, K 3 PO 4 and BaS will be highly alkaline(which is easy to see by how soapy the soda is to the touch) .
An excess of OH ions in a solution can be easily detected with an indicator or measured with special devices (pH meters).
If in a concentrated solution of a salt that is strongly hydrolyzed by the anion,
for example, Na 2 CO 3, add aluminum, then the latter (due to amphotericity) will react with alkali and the release of hydrogen will be observed. This is additional evidence of hydrolysis, because we did not add NaOH alkali to the soda solution!
Pay special attention to salts of medium-strength acids - orthophosphoric and sulfurous. In the first step, these acids dissociate quite well, so their acidic salts do not undergo hydrolysis, and the solution environment of such salts is acidic (due to the presence of a hydrogen cation in the salt). And medium salts hydrolyze at the anion - the medium is alkaline. So, hydrosulfites, hydrogen phosphates and dihydrogen phosphates do not hydrolyze at the anion, the medium is acidic. Sulfites and phosphates are hydrolyzed by anion, the medium is alkaline.
Hydrolysis by cation
When a dissolved salt cation interacts with water, the process is called
hydrolysis of salt at cation
1) Ni(NO 3) 2 = Ni 2+ + 2NO 3 − (dissociation)
2) Ni 2+ + H 2 O ↔ NiOH + + H + (hydrolysis)
The dissociation of the Ni(NO 3) 2 salt occurs completely, the hydrolysis of the Ni 2+ cation occurs to a very small extent (for a 0.1 M solution - by 0.001%), but this is enough for the medium to become acidic (the H + ion is present among the hydrolysis products ).
Only cations of poorly soluble basic and amphoteric hydroxides and ammonium cation undergo hydrolysis NH4+. The metal cation splits off the hydroxide ion from the water molecule and releases the hydrogen cation H +.
As a result of hydrolysis, the ammonium cation forms a weak base - ammonia hydrate and a hydrogen cation:
NH 4 + + H 2 O ↔ NH 3 H 2 O + H +
Please note that you cannot increase the number of water molecules and write hydroxide formulas (for example, Ni(OH) 2) instead of hydroxocations (for example, NiOH +). If hydroxides were formed, then precipitation would form from the salt solutions, which is not observed (these salts form transparent solutions).
Excess hydrogen cations can be easily detected with an indicator or measured with special devices. Magnesium or zinc is added to a concentrated solution of a salt that is strongly hydrolyzed by the cation, and the latter react with the acid to release hydrogen.
If the salt is insoluble, then there is no hydrolysis, because the ions do not interact with water.
Chemistry, like most exact sciences, which 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 is important only for chemist 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 during the interaction of H 2 O with both organic and inorganic substances. Its result directly depends on what the water came into contact with, and also whether additional catalyst substances were used, or whether the temperature and pressure were changed.
For example, the hydrolysis reaction of a salt promotes the formation of acids and alkalis. And if we are talking about organic substances, other products are obtained. Aqueous solvolysis of fats promotes the formation of glycerol and higher fatty acids. If the process occurs with proteins, the result is the formation of various amino acids. Carbohydrates (polysaccharides) are broken down into monosaccharides.
In the human body, which is unable to fully assimilate proteins and carbohydrates, the hydrolysis reaction “simplify” them into substances that the body is able to digest. So solvolysis in water plays an important role in the normal functioning of each biological individual.
Hydrolysis of salts
Having learned about hydrolysis, it is worth familiarizing yourself with its occurrence in substances of inorganic origin, namely salts.
The peculiarity of this process is that when these compounds interact with water, the weak electrolyte ions in 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 latter you can notice instead of one arrow there are two, both 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 is simultaneously not only decomposed into components (which allow new compounds to arise), but also formed again.
However, not all hydrolysis is reversible, otherwise it would not make sense, since the new substances would be unstable.
There are a number of factors that can contribute to such a reaction becoming irreversible:
- Temperature. Whether it increases or decreases determines in which direction the equilibrium in the ongoing reaction shifts. If it becomes 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 increases, the 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
- By anion (ion with a negative charge). Solvolysis in water of salts of acids of weak and strong bases. Due to the properties of the interacting substances, such a reaction 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 implies 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 presented below.
N is the number of molecules of a substance that have undergone hydrolysis, and N0 is their total number in the 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 producing 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 difficult-to-pronounce term refers to fatty acids, which most of us know as fats.
They come in both animal and plant origin. However, everyone knows that water is not capable of dissolving such substances, so how does fat hydrolysis occur?
The reaction in question is called saponification of fats. This is aqueous solvolysis of triacylglycerols under the influence of enzymes in an alkaline or acidic environment. Depending on it, alkaline and acid hydrolysis are distinguished.
In the first case, the reaction results in the formation of salts of higher fatty acids (better known to everyone as soaps). 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 is worth noting that it can be freely carried out in fats of both plant and animal origin.
The reaction in question is the reason that soap washes rather poorly in hard water and does not wash 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 the water, again undergoes hydrolysis, breaking down into sodium ions and a hydrocarbon residue. As a result of the interaction of these substances, insoluble salts are formed in water, which look like white flakes. To prevent this from happening, sodium bicarbonate NaHCO 3, better known as baking soda, is added to the water. This substance increases the alkalinity of the solution and thereby helps the soap perform its functions. By the way, to avoid such troubles, in modern industry synthetic detergents are made from other substances, for example from salts of esters of higher alcohols and sulfuric acid. Their molecules contain from twelve to fourteen carbon atoms, due to which they do not lose their properties in salty or hard water.
If the environment in which the reaction occurs is acidic, the process is called acid hydrolysis of triacylglycerols. In this case, under the influence of a certain acid, the 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 purification, such as removing traces of acetylene from ethylene or oxygen impurities from various systems.
Hydrolysis of carbohydrates
The substances in question are among the most important components of human and animal food. However, the body is not able to absorb sucrose, lactose, maltose, starch and glycogen in their pure form. Therefore, as in the case of fats, these carbohydrates are broken down into digestible elements using a hydrolysis reaction.
Aqueous solvolysis of carbons is also actively used in industry. From starch, as a result of the reaction in question with H 2 O, glucose and molasses are extracted, which are included in 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 the well-known ethyl alcohol are extracted from it.
Hydrolysis of cellulose occurs under prolonged exposure to high temperature and the presence of mineral acids. The end product of this reaction is, as in the case of starch, glucose. It should be taken into account 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 walls of all higher plants, the 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 suited for nutrition.
Protein hydrolysis
Proteins are the main building material for the cells of all living organisms. They consist of numerous amino acids and are a very important product for the normal functioning of the body. However, being high-molecular compounds, they can be poorly absorbed. To simplify this task, they are hydrolyzed.
As with other organic substances, this reaction breaks down proteins into low molecular weight products that are easily absorbed by the body.
Hydrolysis of esters occurs reversibly in an acidic environment (in the presence of an inorganic acid) to form the corresponding alcohol and carboxylic acid.
To shift the chemical equilibrium towards the reaction products, hydrolysis is carried out in the presence of alkali.
Historically, the first example of such a reaction was the alkaline cleavage of higher fatty acid esters to produce soap. This happened in 1811, when the French scientist E. Chevreul. By heating fats with water in an alkaline environment, he obtained glycerin and soaps - salts of higher carboxylic acids. Based on this experiment, the composition of fats was established; they turned out to be esters, but only “triple esters,” derivatives of the trihydric alcohol glycerol - triglycerides. And the process of hydrolysis of esters in an alkaline environment is still called “saponification.”
For example, saponification of an ester formed by glycerin, palmitic and stearic acids:
Sodium salts of higher carboxylic acids are the main components of solid soap, potassium salts are the main components of liquid soap.
The French chemist M. Berthelot in 1854 carried out the esterification reaction and synthesized fat for the first time. Consequently, the hydrolysis of fats (as well as other esters) is reversible. The reaction equation can be simplified as follows:
Enzymatic hydrolysis of fats occurs in living organisms. In the intestine, under the influence of the lipase enzyme, food fats are hydrated into glycerol and organic acids, which are absorbed by the intestinal walls, and new fats characteristic of the given organism are synthesized in the body. They travel through the lymphatic system into the blood and then into the adipose tissue. From here, fats enter other organs and tissues of the body, where, in the process of metabolism in cells, they are again hydrolyzed and then gradually oxidized to carbon monoxide and water, releasing the energy necessary for life.
In technology, hydrolysis of fats is used to obtain glycerin, higher carboxylic acids, and soap.
Hydrolysis of carbohydrates
As you gape, carbohydrates are the most important components of our food. Moreover, di- (sucrose, lactose, maltose) and polysaccharides (starch, glycogens) are not directly absorbed by the body. They, like fats, first undergo hydrolysis. Starch hydrolysis occurs in stages.
In laboratory and industrial conditions, acid is used as a catalyst for these processes. Reactions are carried out by heating.
The reaction of hydrolysis of starch to glucose under the catalytic action of sulfuric acid was carried out in 1811 by the Russian scientist K. S. Kirchhoff.
In the human and animal bodies, hydrolysis of carbohydrates occurs under the action of enzymes (Scheme 4).
Industrial hydrolysis of starch produces glucose and molasses (a mixture of dextrins, maltose and glucose). Molasses is used in confectionery.
Dextrins, as a product of partial hydrolysis of starch, have an adhesive effect: they are associated with the appearance of a crust on bread and fried potatoes, as well as the formation of a dense film on linen covered with malene under the influence of a hot iron.
Another polysaccharide you know - cellulose - can also be hydrolyzed to glucose when heated for a long time with mineral acids. The process proceeds step by step, but briefly. This process underlies many hydrolysis industries. They are used to obtain food, feed and technical products from non-food plant raw materials - waste from logging, wood processing (sawdust, shavings, wood chips), processing of agricultural crops (straw, seed husks, corn cobs, etc.).
The technical products of such industries are glycerin and ethylene glycol. organic acids, feed yeast, ethyl alcohol, sorbitol (six-atom alcohol).
Protein hydrolysis
Hydrolysis can be suppressed (significantly reducing the amount of salt undergoing hydrolysis).
a) increase the concentration of the solute
b) cool the solution;
a) introduce one of the hydrolysis products into the solution; for example, acidify the solution if it is acidic as a result of hydrolysis, or alkalize it if it is alkaline.
Meaning of hydrolysis
Hydrolysis of salts has both practical and biological significance.
Even in ancient times, mola was used as a detergent. The ash contains potassium carbonate, which hydrolyzes into an anion in water; the aqueous solution becomes soapy due to the OH ions formed during hydrolysis.
Currently, in everyday life we use soap, washing powders and other detergents. The main component of soap is sodium or potassium salts of higher fatty carboxylic acids: stearates, palmitates, which are hydrolyzed.
Salts of inorganic acids (phosphates, carbonates) are specially added to the composition of washing powders and other detergents, which enhance the cleaning effect by increasing the pH of the environment.
Salts that create the necessary alkaline solution are contained in the photographic developer. These are sodium carbonate, potassium carbonate, borax and other salts that are hydrolyzed by the anion.
If the acidity of the soil is insufficient, the plants develop a disease - chlorosis. Its signs are yellowing or whitening of leaves, retarded growth and development. If the pH is > 7.5, then ammonium sulfate fertilizer is added to it, which helps to increase acidity due to hydrolysis of the cation occurring in the soil.
The biological role of hydrolysis of certain salts that make up the body is invaluable. 
Please note that in all hydrolysis reactions, the oxidation states of the chemical elements do not change. Redox reactions are usually not classified as hydrolysis reactions, although the substance interacts with water.
What factors can influence the degree of hydrolysis
As you already know, from the definition, hydrolysis is the process of decomposition using water. In a solution, salts are present in the form of ions and their driving force, which provokes such a reaction, is called the formation of low-dissociating particles. This phenomenon is characteristic of many reactions occurring in solutions.
But ions, when interacting with water, do not always create slightly dissociating particles. So, as you already know that salt is made up of a cation and an anion, the following types of hydrolysis are possible:
If water reacts with a cation, we get hydrolysis of the cation;
If water reacts only with an anion, then we obtain hydrolysis at the anion;
When a cation and anion react simultaneously with water, we obtain joint hydrolysis.
Because we already know that hydrolysis has a reversible reaction, the state of its equilibrium is influenced by several factors, which include: temperature, concentration of hydrolysis products, concentrations of reaction participants, additions of foreign substances. But, when gaseous substances do not take part in the reaction, then these substances do not affect the pressure, with the exception of water, since its concentration is constant.
Now let's look at examples of expressions for hydrolysis constants:
Temperature can be a factor that affects the equilibrium state of hydrolysis. Thus, with increasing temperature, the equilibrium of the system shifts to the right and in this case the degree of hydrolysis increases.
If we follow Le Chatelier's principles, we see that as the concentration of hydrogen ions increases, the equilibrium shifts to the left, while the degree of hydrolysis decreases, and as the concentration increases, we see the effect on the reaction in the second formula.
With the concentration of salts, we can observe that the equilibrium in the system shifts to the right, however, the degree of hydrolysis, if we follow Le Chatelier’s principles, decreases. If we consider this process from the point of view of a constant, we will see that with the addition of phosphate ions, the equilibrium will shift to the right and their concentration will increase. That is, to double the concentration of hydroxide ions, it is necessary to increase the concentration of phosphate ions fourfold, although the value of the constant should not change. From this it follows that the relationship 
will decrease by 2 times.
With the dilution factor, there is a simultaneous decrease in the particles that are in the solution, except for water. If we follow Le Chatelier's principle, we see that the equilibrium shifts and the number of particles increases. But this hydrolysis reaction occurs without taking into account water. In this case, the dilution of the equilibrium shifts towards the course of this reaction, that is, to the right and it is natural that the degree of hydrolysis will increase.
The equilibrium position can be affected by additions of foreign substances, provided that they react with one of the participants in the reaction. For example, if we add a solution of sodium hydroxide to a solution of copper sulfate, then the hydroxide ions present in it will begin to interact with hydrogen ions. In this case, it follows from Le Chatelier’s principle that eventually the concentration will decrease, the equilibrium will shift to the right, and the degree of hydrolysis will increase. Well, when sodium sulfide is added to the solution, the equilibrium will shift to the left, due to the binding of copper ions into practically insoluble copper sulfide.
Let us summarize the material studied and come to the conclusion that the topic of hydrolysis is not complicated, but it is necessary to clearly understand what hydrolysis is, have a general understanding of the shift in chemical equilibrium and remember the algorithm for writing equations.
Tasks
1. Select examples of organic substances that undergo hydrolysis:
glucose, ethanol, bromomethane, methanal, sucrose, methyl formic acid, stearic acid, 2-methyl butane.
Write down equations for hydrolysis reactions; in the case of reversible hydrolysis, indicate the conditions that allow the chemical equilibrium to shift towards the formation of the reaction product.
2. Which salts undergo hydrolysis? What kind of environment can aqueous solutions of salts have? Give examples.
3. Which salts undergo cation hydrolysis? Write down equations for their hydrolysis and indicate the medium.
Transcript
1 HYDROLYSIS OF ORGANIC AND INORGANIC SUBSTANCES
2 Hydrolysis (from the ancient Greek “ὕδωρ” water and “λύσις” decomposition) is one of the types of chemical reactions where, when substances interact with water, the original substance decomposes with the formation of new compounds. The mechanism of hydrolysis of compounds of various classes: - salts, carbohydrates, fats, esters, etc. has significant differences
3 Hydrolysis of organic substances Living organisms carry out the hydrolysis of various organic substances during 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, 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 feed yeast, wax, fertilizers, etc.
4 1. Hydrolysis of organic compounds fats are hydrolyzed to produce glycerol and carboxylic acids (with NaOH saponification):
5 starch and cellulose are hydrolyzed to glucose:
7 TEST 1. During the hydrolysis of fats, 1) alcohols and mineral acids are formed 2) aldehydes and carboxylic acids 3) monohydric alcohols and carboxylic acids 4) glycerin and carboxylic acids ANSWER: 4 2. Hydrolysis is subject to: 1) Acetylene 2) Cellulose 3) Ethanol 4) Methane ANSWER: 2 3. Hydrolysis is subject to: 1) Glucose 2) Glycerol 3) Fat 4) Acetic acid ANSWER: 3
8 4. The hydrolysis of esters produces: 1) Alcohols and aldehydes 2) Carboxylic acids and glucose 3) Starch and glucose 4) Alcohols and carboxylic acids ANSWER: 4 5. The hydrolysis of starch produces: 1) Sucrose 2) Fructose 3) Maltose 4) Glucose ANSWER: 4
9 2. Reversible and irreversible hydrolysis Almost all considered reactions of hydrolysis of organic substances are reversible. But there is also irreversible hydrolysis. A 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. Saz₂ + 2n₂o = sa (it) ₂ + s₂n₂ with hydrolysis of salts: al₄c₃ + 12 h₂o = 4 al (oh) ₃ + 3ch₄ al₂s₃ + 6 h₂o cah₂ + 2 h₂o = 2 al (Оh) ₃ + 3 h₂s = 2ca (oh )₂ + H₂
10 HYDROLYSIS OF SALTS Hydrolysis of salts is a type of hydrolysis reaction 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”). A distinction is made 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 a salt of a weak acid and a weak base (irreversible) A 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 (hydrolysis by an anion): (the solution has an alkaline medium, the reaction proceeds reversibly, hydrolysis in the second stage occurs to an insignificant extent) 2. Hydrolysis of a salt of a strong acid and a weak base (hydrolysis by a cation): (the solution has an acidic medium, the reaction is reversible, hydrolysis in the second stage occurs to an insignificant extent)
13 3. Hydrolysis of a salt of a weak acid and a weak base: (equilibrium is shifted towards the products, 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]+ ALKALINE MEDIUM ACIDIC SALT, hydrolysis by ANION
15 First stage of hydrolysis Na₂CO₃ + H₂O NaOH + NaHCO₃ 2Na+ + CO₃ ² + H₂O Na+ + OH + Na+ + HCO₃ CO₃ ² + H₂O OH + HCO₃ Second stage of hydrolysis NaHCO₃ + H₂O = NaOH + H₂CO ₃ CO₂ H ₂O Na+ + HCO₃ + H₂O = Na+ + OH + CO₂ + H₂O HCO₃ + H₂O = OH + CO₂ + H₂O
16 SCHEME FOR HYDROLYSIS OF COPPER (II) CHLORIDE 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 SCHEME FOR HYDROLYSIS OF ALUMINUM SULPHIDE Al₂S₃ Al(OH)₃ H₂S weak base weak acid = [H]+ NEUTRAL REACTION OF THE MEDIUM hydrolysis irreversible
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 hydrolysis does not occur NaCl + H₂O = NaOH + HCl Na+ + Cl + H₂O = Na+ + OH + H+ + Cl
20 Transformation of the earth's crust Providing a slightly alkaline environment in sea water THE ROLE OF HYDROLYSIS IN HUMAN LIFE Washing Washing dishes Washing with soap Digestive processes
21 Write the hydrolysis equations: A) K₂S B) FeCl₂ C) (NH₄)₂S D) BaI₂ K₂S: KOH - strong base H₂S weak acid HYDROLYSIS BY ANION SALT ACIDIC ALKALINE K₂S + H₂O KHS + KOH 2K+ + S ² + H₂O K+ + ( FeOH)+ + Cl + H+ + Cl Fe +² + H₂O (FeOH)+ + H+
22 (NH₄)₂S: NH₄OH - weak base; H₂S - weak acid IRREVERSIBLE HYDROLYSIS (NH₄)₂S + 2H₂O = H₂S + 2NH₄OH 2NH₃ 2H₂O BaI₂ : Ba(OH)₂ - strong base; HI - strong acid NO HYDROLYSIS
23 Complete on a piece of paper. At the next lesson, hand in your work to the teacher.
25 7. An aqueous solution of which salt has a neutral medium? a) Al(NO₃)₃ b) ZnCl₂ c) BaCl₂ d) Fe(NO₃)₂ 8. In which solution will the litmus color 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 are not subject to hydrolysis 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 environment as a result of hydrolysis of sodium carbonate is 1) alkaline 2) strongly acidic 3) acidic 4) neutral 12. Hydrolysis is subjected to 1) CH 3 COOK 2) KCI 3) CaCO 3 4) Na 2 SO 4
27 13. The following are not subject to hydrolysis: 1) ferrous sulfate 2) alcohols 3) ammonium chloride 4) esters 14. The solution medium as a result of ammonium chloride hydrolysis: 1) weakly alkaline 2) strongly alkaline 3) acidic 4) neutral
28 PROBLEM Explain why when the solutions - FeCl₃ and Na₂CO₃ - are merged, a precipitate forms 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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