Copper hydroxide is a weak or strong base. Strong and weak electrolytes (2023)

All acids, their properties and bases are divided into strong and weak. But don't you dare confuse concepts like "strong acid" or "strong base" with their concentration. For example, you cannot make a strong solution of a weak acid or a dilute solution of a strong base. For example, hydrochloric acid, when dissolved in water, gives each of two water molecules one of its protons.

When a chemical reaction takes place on the hydronium ion, the hydrogen ion binds tightly to the water molecule. The reaction itself will continue until its reagents are completely used up. Our water in this case plays the role of a base, as it receives a proton from hydrochloric acid. Acids that completely dissociate in aqueous solutions are called strong acids.

When we know the initial concentration of a strong acid, in this case it is not difficult to calculate the concentration of hydronium ions and chloride ions in the solution. For example, if you take and dissolve 0.2 mol of gaseous hydrochloric acid in 1 liter of water, the ion concentration after dissociation will be exactly the same.

Examples of strong acids:

1)HCl, hydrochloric acid;
2)HBr, hydrogen bromide;
3)HI, hydrogen iodine;
4)HNO3, nitric acid;
5)HClO4 - perchloric acid;
6)H2SO4 is sulfuric acid.

All known acids (with the exception of sulfuric acid) are listed above and are monoprotic in that their atoms donate one proton each; Sulfuric acid molecules can easily donate two of their protons, so sulfuric acid is diprotic.

Electrolytes are strong bases; they completely dissociate in aqueous solutions to form a hydroxide ion.

As with acids, calculating the hydroxide ion concentration is very easy once you know the initial concentration of the solution. For example, a NaOH solution with a concentration of 2 mol/l dissociates at the same ion concentration.

weak acids. foundations and properties

As for weak acids, they do not dissociate completely, that is, partially. It is very easy to distinguish between strong and weak acids: if the reference table shows its constant next to the name of an acid, then that acid is weak; if the constant is not given, then this acid is strong.

Weak bases also react well with water to form an equilibrium system. Weak acids are also characterized by a dissociation constant K.

The hydrolysis constant is equal to the ratio of the product of the concentrations of hydrolysis products and the concentration of unhydrolyzed salt.

Example 1Calculate the degree of hydrolysis of NH 4 Cl.

Decision:From the table we find Kd (NH 4 OH) \u003d 1.8 ∙ 10 -3, from here

Kγ \u003d Kv / Kd k \u003d \u003d 10 -14 / 1,8 10 -3 \u003d 5,56 10 -10.

Example 2Calculate the degree of hydrolysis of ZnCl 2 in 1 step in a 0.5 M solution.

Decision:Ionic equation for the hydrolysis of Zn 2 + H 2 OZnOH + + H +

KdZnOH+1=1.5∙10-9; hγ=√(Kv/ [basic Kd ∙Cm]) = 10 -14 /1.5∙10 -9 ∙0.5=0.36∙10 -2 (0.36%).

Example 3Compose ionic-molecular and molecular equations for salt hydrolysis: a) KCN; b) Na2CO3; c) ZnSO4. Determine the reaction of half solutions of these salts.

Decision:a) Potassium cyanide KCN is a salt of a weak monobasic acid (see Appendix Table I) HCN and a strong base KOH. When dissolved in water, KCN molecules completely dissociate into K+ cations and CN- anions. K + cations cannot bind to OH - water ions, as KOH is a strong electrolyte. CN - anions bind to H+ ions in water, forming molecules of a weak electrolyte HCN. The salt hydrolyses to the anion. Ionic-molecular hydrolysis equation

CN - + H 2 OHCN+OH-

or in molecular form

Parque Industrial + H 2 OHCN + KOH

As a result of hydrolysis, a certain excess of OH - ions appears in the solution; therefore, the KCN solution has an alkaline reaction (pH > 7).

b) Sodium carbonate Na 2 CO 3 is a salt of a weak polybasic acid and a strong base. In this case, the anions of the CO 3 2- salt, which bind to the hydrogen ions of the water, form anions of the acid salt of HCO - 3, and not molecules of H 2 CO 3, since the HCO - 3 ions they dissociate much harder than H2CO3 molecules. Under normal conditions, hydrolysis occurs in the first stage. The salt hydrolyses to the anion. Ionic-molecular hydrolysis equation

CO2-3+ H 2 OHCO - 3 + OH -

or in molecular form

Na2CO3 + H2O NaHCO3 + NaOH

An excess of OH - ions appears in the solution, so the Na 2 CO 3 solution has an alkaline reaction (pH > 7).

c) Zinc sulfate ZnSO 4 - a salt of a weak polyacid base Zn (OH) 2 and a strong acid H 2 SO 4. In this case, the Zn + cations bind to the hydroxide ions of water, forming cations of the basic salt ZnOH + . The formation of Zn(OH) 2 molecules does not occur, as ZnOH + ions dissociate much more difficult than Zn(OH) 2 molecules. Under normal conditions, hydrolysis occurs in the first stage. The salt hydrolyses to the cation. Ionic-molecular hydrolysis equation

Zn 2+ + H 2 OZnOH + + H +

or in molecular form

2ZnSO4 + 2H2O (ZnOH)2SO4 + H2SO4

An excess of hydrogen ions appears in the solution, so the ZnSO 4 solution has an acidic reaction (pH < 7).

Example 4What products are formed when A1(NO 3) 3 and K 2 CO 3 solutions are mixed? Make an ion-molecular and molecular reaction equation.

Decision.The salt A1 (NO 3) 3 is hydrolyzed by the cation and K 2 CO 3 - by the anion:

A1 3+ + H2OA1OH 2+ + H +

CO2-3+H2OHCO - s + OH -

If the solutions of these salts are in the same container, then there is a mutual increase in the hydrolysis of each of them, because the H + and OH - ions form a weak electrolyte H 2 O molecule. right and the hydrolysis of each of the salts taken goes to the end with the formation of A1 (OH) 3 and CO 2 (H 2 CO 3). Ionic-molecular equation:

2A1 3+ + ZSO 2- 3+ZN 2 O \u003d 2A1 (OH) 3 + ZSO 2

molecular equation: ZSO 2 + 6KNO 3

2A1 (NO 3) 3 + ZK 2 CO 3 + ZN 2 O \u003d 2A1 (OH) 3

Before talking about the chemical properties of amphoteric bases and hydroxides, let's clearly define what they are.

1) Bases or basic hydroxides include metallic hydroxides in the +1 or +2 oxidation state, that is, whose formulas are written as MeOH or as Me(OH) 2 . However, there are exceptions. Therefore, the hydroxides Zn (OH) 2, Be (OH) 2, Pb (OH) 2, Sn (OH) 2 do not belong to the bases.

2) Amphoteric hydroxides include metallic hydroxides in the +3, +4 oxidation state and, as exceptions, hydroxides Zn(OH) 2, Be(OH) 2, Pb(OH) 2, Sn(OH) 2. The +4 oxidation state is not found in USE assignments, so they will not be considered.

Chemical properties of bases.

All bases are divided into:

Remember that beryllium and magnesium are not alkaline earth metals.

In addition to being soluble in water, alkalis also dissociate very well in aqueous solutions, while insoluble bases show a low degree of dissociation.

This difference in solubility and dissociation ability between insoluble alkalis and hydroxides leads, in turn, to remarkable differences in their chemical properties. Thus, in particular, alkalis are chemically more active compounds and are often able to participate in those reactions in which insoluble bases do not participate.

Reaction of bases with acids.

Alkalis absolutely react with all acids, even very weak and insoluble ones. For example:

Insoluble bases react with almost all soluble acids, they do not react with insoluble silicic acid:

It should be noted that both strong and weak bases with the general formula of the form Me (OH) 2 can form basic salts with a lack of acid, for example:

Interaction with acid oxides

Alkalis react with all acid oxides to form salts and often water:

Insoluble bases can react with all higher acid oxides corresponding to stable acids, for example P 2 O 5, SO 3, N 2 O 5, with the formation of medium salts:

Insoluble bases of the Me(OH) 2 form react in the presence of water with carbon dioxide exclusively with the formation of basic salts. For example:

Cu(OH)2 + CO2 = (CuOH)2CO3 + H2O

With silicon dioxide, due to its exceptional inertness, only the strongest bases, alkalis, react. In this case, normal salts are formed. The reaction does not occur with insoluble bases. For example:

Interaction of bases with amphoteric oxides and hydroxides

All alkalis react with amphoteric oxides and hydroxides. If the reaction is carried out by fusing an amphoteric oxide or hydroxide with a solid alkali, such a reaction leads to the formation of free hydrogen salts:

If alkaline aqueous solutions are used, hydroxocomplex salts are formed:

In the case of aluminum, under the action of an excess of concentrated alkali, instead of the Na salt, the Na3 salt is formed:

The interaction of bases with salts.

Any base reacts with any salt only if two conditions are met simultaneously:

1) solubility of starting compounds;

2) the presence of a precipitate or gas among the reaction products

For example:

Thermal stability of bases

All alkalis, except Ca(OH) 2 , are heat resistant and melt without decomposition.

All insoluble bases, as well as slightly soluble Ca(OH) 2 , decompose when heated. The highest decomposition temperature for calcium hydroxide is around 1000°C:

Insoluble hydroxides have much lower decomposition temperatures. So, for example, copper(II) hydroxide already decomposes at temperatures above 70°C:

Chemical properties of amphoteric hydroxides

Interaction of amphoteric hydroxides with acids.

Amphoteric hydroxides react with strong acids:

Amphoteric metal hydroxides in the +3 oxidation state, i.e. Me(OH) 3 type, do not react with acids such as H 2 S, H 2 SO 3 and H 2 CO 3 because the salts that can be formed as a result of such reactions are subject to irreversible hydrolysis to the original amphoteric hydroxide and the corresponding acid:

Interaction of amphoteric hydroxides with acidic oxides

Amphoteric hydroxides react with higher oxides, which correspond to stable acids (SO 3, P 2 O 5, N 2 O 5):

Amphoteric metallic hydroxides in the +3 oxidation state, that is, Me (OH) 3 type, do not react with the acidic oxides SO 2 and CO 2.

Interaction of amphoteric hydroxides with bases.

Of the bases, amphoteric hydroxides react only with alkalis. In this case, if an alkaline aqueous solution is used, hydroxocomplex salts are formed:

And when amphoteric hydroxides are fused with solid alkalis, their anhydrous analogues are obtained:

Interaction of amphoteric hydroxides with basic oxides

Amphoteric hydroxides react when fused with oxides of alkali and alkaline earth metals:

Thermal decomposition of amphoteric hydroxides

All amphoteric hydroxides are insoluble in water and, like any insoluble hydroxide, decompose when heated to the corresponding oxide and water.

Salt hydrolysis" - To get an idea of ​​\u200b\u200bchemistry as a productive force of society. Acetic acid CH3COOH is the oldest of organic acids. In acids - carboxyl groups, but all acids here are weak.

All acids, their properties and bases are divided into strong and weak. For example, you cannot make a strong solution of a weak acid or a dilute solution of a strong base. Our water in this case plays the role of a base, as it receives a proton from hydrochloric acid. Acids that completely dissociate in aqueous solutions are called strong acids.

For hydrated oxides with an indefinite number of water molecules, for example Tl2O3 n H2O, it is unacceptable to write formulas like Tl(OH)3. It is also not recommended to call these compounds hydroxides.

For bases, one can quantify their strength, that is, the ability to separate a proton from an acid. All bases are solid with different colors. Attention! Alkalis are highly caustic substances. If it comes into contact with the skin, alkaline solutions cause severe long-lasting burns, if they come into contact with the eyes they can cause blindness. When arsenic-containing cobalt ores are roasted, volatile toxic arsenic oxide is released.

You already know these properties of the water molecule. II) and an acetic acid solution. HNO2) - only one proton.

All bases are solids that have different colors. 1. Act on indicators. Indicators change color depending on interaction with different chemicals. When interacting with bases, they change color: the methyl orange indicator turns yellow, the litmus indicator turns blue, and phenolphthalein turns fuchsia.

Cool containers, for example, by placing them in a container filled with ice. Three solutions will remain clear and the fourth will quickly become cloudy, a white precipitate will begin to fall out. This is where barium salt is found. Set this container aside. You can quickly determine barium carbonate in another way. This is very easy to do, all you need are porcelain evaporating cups and a lamp. If it is a lithium salt, the color will be bright red. By the way, if barium salt were tested in the same way, the color of the flame should be green.

An electrolyte is a substance that in the solid state is dielectric, that is, it does not conduct electric current, but in dissolved or molten form it becomes conductive. Remember that the degree of dissociation and, consequently, the strength of the electrolyte depends on many factors: the nature of the electrolyte itself, the solvent and the temperature. Therefore, this division itself is to some extent conditional. After all, the same substance can, under different conditions, be both a strong electrolyte and a weak electrolyte.

Hydrolysis does not occur, new compounds are not formed, the acidity of the medium does not change. How does the acidity of the environment change? The reaction equations cannot yet be written. It remains for us to sequentially discuss 4 groups of salts and for each of them to give a specific "scenario" of hydrolysis. In the next part, we'll start with salts formed by a weak base and a strong acid.

After reading the article, you will be able to separate substances into salts, acids and bases. H solution, what are the general properties of acids and bases. If they refer to the definition of a Lewis acid, then in the text such an acid is called a Lewis acid.

The smaller this value, the stronger the acid. Strong or weak - this is required in the Ph.D. look, but you need to know the classics. Strong acids are acids that can displace the anion of another acid in the salt.

we definehydrolysisremembered some facts aboutsales🇧🇷 We will now discuss strong and weak acids and discover that the "setup" of hydrolysis depends precisely on which acid and which base formed that salt.

← Hydrolysis of salts. Part I

Strong and weak electrolytes.

Let me remind you that all acids and bases can be conditionally divided intoForteyweak🇧🇷 Strong acids (and, in general, strong electrolytes) dissociate almost completely in aqueous solution. Weak electrolytes break down into ions to a small extent.

Strong acids include:

• H 2 SO 4 (sulfuric acid),
• HClO 4 (perchloric acid),
• HClO3 (hydrochloric acid),
• HNO 3 (nitric acid),
• HCl (hydrochloric acid),
• HBr (hydrobromic acid),
• HI (ioditric acid).

The following is a list of weak acids:

• H 2 SO 3 (sulfurous acid),
• H 2 CO 3 (carbonic acid),
• H 2 SiO 3 (silicic acid),
• H 3 PO 3 (phosphorous acid),
• H 3 PO 4 (orthophosphoric acid),
• HClO 2 (chlorous acid),
• HClO (hypochlorous acid),
• HNO 2 (nitrous acid),
• HF (hydrofluoric acid),
• H 2 S (hydrosulfuric acid),
• most organic acids, e.g. acetic acid (CH3COOH).

Naturally, it is impossible to list all the acids that exist in nature. Only the most "popular" ones are listed. It should also be understood that the division of acids into strong and weak is quite arbitrary.

Things are much simpler with strong and weak foundations. You can use the solubility table. All strong bases aresolublein base water, except NH 4 OH. These substances are called alkalis (NaOH, KOH, Ca(OH) 2, etc.)

The weak bases are:

• all hydroxides insoluble in water (e.g. Fe(OH) 3 , Cu(OH) 2 etc.),
• NH 4 OH (ammonium hydroxide).

Salt hydrolysis. key facts

It may seem to those who read this article that we have already forgotten the main topic of the conversation and passed it to the side. This is not true! Our conversation about acids and bases, about strong and weak electrolytes is directly related to the hydrolysis of salts. Now you will convince yourself of this.

So let me give you the basic facts:

1. Not all salts undergo hydrolysis. Existshydrolytically stablecompounds such as sodium chloride.
2. Salt hydrolysis can be complete (irreversible) and partial (reversible).
3. During the hydrolysis reaction, an acid or a base is formed, the acidity of the medium changes.
4. The fundamental possibility of hydrolysis, the direction of the corresponding reaction, its reversibility or irreversibility are determined.acid poweryby the strength of the foundationthat make up this salt
5. Depending on the strength of the corresponding acid and resp. bases, all salts can be divided into4 groups🇧🇷 Each of these groups has its own "stage" of hydrolysis.

Example 4🇧🇷 The NaNO 3 salt is formed by a strong acid (HNO 3) and a strong base (NaOH). Hydrolysis does not occur, new compounds are not formed, the acidity of the medium does not change.

Example 5🇧🇷 The NiSO 4 salt is formed by a strong acid (H 2 SO 4) and a weak base (Ni(OH) 2). Hydrolysis takes place on the cation, during the reaction an acid and a basic salt are formed.

Example 6🇧🇷 Potassium carbonate is formed from a weak acid (H 2 CO 3) and a strong base (KOH). Hydrolysis of anions, formation of alkaline and acidic salts. alkaline solution.

Example 7🇧🇷 Aluminum sulfide is formed by a weak acid (H 2 S) and a weak base (Al (OH) 3). Hydrolysis takes place on both the cation and the anion. irreversible reaction. During the process, H 2 S and aluminum hydroxide are formed. The acidity of the environment changes slightly.

Try it yourself:

Exercise 2🇧🇷 What type are the following salts: FeCl 3 , Na 3 PO 3 , KBr, NH 4 NO 2 ? Do these salts undergo hydrolysis? Cation or anion? What is formed during the reaction? How does the acidity of the environment change? The reaction equations cannot yet be written.

It remains for us to sequentially discuss 4 groups of salts and give a specific hydrolysis "scenario" for each of them. In the next part, we'll start with salts formed by a weak base and a strong acid.