Molecular and molecular-ionic equations. Ionic reaction equations

Instructions

On the left side of the equation, write the substances involved in the chemical reaction. They are called "raw materials". On the right side, respectively, are the formed substances (“reaction products”).

The number of atoms of all elements on the left and right sides of the reaction must be . If necessary, “balance” the quantity by selecting coefficients.

When writing an equation chemical reaction, first make sure that it is even possible. That is, that its occurrence does not contradict the known physical and chemical rules and properties of substances. For example, the reaction:

NaI + AgNO3 = NaNO3 + AgI

It proceeds quickly and completely; during the reaction, an insoluble light yellow precipitate of silver iodide is formed. And the reverse reaction:

AgI + NaNO3 = AgNO3 + NaI - impossible, although written down with the correct characters, and the number of atoms of all elements on the left and right sides is the same.

Write the equation in "full" form, that is, using their molecular formulas. For example, the reaction for the formation of sulfate precipitate:

BaCl2 + Na2SO4 = 2NaCl + BaSO4

Or you can write the same reaction in ionic form:

Ba 2+ + 2Cl- + 2Na+ + SO4 2- = 2Na+ + 2Cl- + BaSO4

In the same way, you can write the equation of another reaction in ionic form. Remember that each molecule of a soluble (dissociating) substance is written in ionic form, identical ions on the left and right sides of the equation are excluded.

A tangent to a curve is a straight line that is adjacent to this curve at given point, that is, it passes through it in such a way that in a small area around this point you can replace the curve with a tangent segment without much loss of accuracy. If this curve is a graph of a function, then the tangent to it can be constructed using a special equation.

Instructions

Let's say you have a graph of some function. Through two points lying on this, a straight line can be drawn. Such a line intersecting the graph of a given function at two points is called a secant.

If, leaving the first point in place, you gradually move the second point in its direction, then the secant will gradually begin to rotate, tending to some specific position. Eventually, when the two points merge into one, the secant will fit snugly against yours at that single point. In other words, the secant will turn into a tangent.

Any inclined (that is, not vertical) line on the coordinate plane is a graph of the equation y = kx + b. The secant passing through the points (x1, y1) and (x2, y2) must therefore satisfy the conditions:
kx1 + b = y1, kx2 + b = y2.
Solving this system of two linear equations, we get: kx2 - kx1 = y2 - y1. Thus k = (y2 - y1)/(x2 - x1).

When the distance between x1 and x2 approaches zero, the differences turn into differentials. Thus, in the equation of the tangent passing through the point (x0, y0), the coefficient k will be equal to ∂y0/∂x0 = f′(x0), that is, the value of the derivative of the function f(x) at the point x0.

To find out the coefficient b, we substitute the already calculated value of k into the equation f′(x0)*x0 + b = f(x0). Solving this equation for b, we get that b = f(x0) - f′(x0)*x0.

As an example, consider the equation of the tangent to the function f(x) = x^2 at the point x0 = 3. The derivative of x^2 is equal to 2x. Therefore, the tangent equation takes the form:
y = 6*(x - 3) + 9 = 6x - 9.
The correctness of this equation is easy

2.6 Ionic-molecular equations

When any strong acid is neutralized by any strong base, about 57.6 kJ of heat is released for each mole of water formed:

HCl + NaOH = NaCl + H 2 O + 57.53 kJ

HNO 3 + KOH = KNO 3 + H 2 O +57.61 kJ

This suggests that such reactions are reduced to one process. We will obtain the equation for this process if we consider in more detail one of the given reactions, for example, the first. Let's rewrite its equation, writing strong electrolytes in ionic form, since they exist in solution in the form of ions, and weak electrolytes in molecular form, since they are in solution mainly in the form of molecules (water is a very weak electrolyte):

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

Considering the resulting equation, we see that during the reaction the Na + and Cl - ions did not undergo changes. Therefore, we will rewrite the equation again, eliminating these ions from both sides of the equation. We get:

H + + OH - = H 2 O

Thus, the reactions of neutralization of any strong acid with any strong base come down to the same process - the formation of water molecules from hydrogen ions and hydroxide ions. It's clear that thermal effects these reactions should also be the same.

Strictly speaking, the reaction of the formation of water from ions is reversible, which can be expressed by the equation

H + + OH - ↔ H 2 O

However, as we will see below, water is a very weak electrolyte and dissociates only to a negligible extent. In other words, the equilibrium between water molecules and ions is strongly shifted towards the formation of molecules. Therefore, in practice, the reaction of neutralization of a strong acid with a strong base proceeds to completion.

When mixing a solution of any silver salt with hydrochloric acid or with a solution of any of its salts, a characteristic white cheesy precipitate of silver chloride is always formed:

AgNO 3 + HC1 = AgCl↓ + HNO 3

Ag 2 SO 4 + CuCl 2 = 2AgCl↓ + CuSO 4

Such reactions also come down to one process. In order to obtain its ionic-molecular equation, we rewrite, for example, the equation of the first reaction, writing strong electrolytes, as in the previous example, in ionic form, and the substance in the sediment in molecular form:

Ag + + NO 3 - + H + + C1 - = AgCl↓+ H + + NO 3 -

As can be seen, the H + and NO 3 - ions do not undergo changes during the reaction. Therefore, we exclude them and rewrite the equation again:

Ag + + С1 - = AgCl↓

This is the ion-molecular equation of the process under consideration.

Here it must also be borne in mind that the silver chloride precipitate is in equilibrium with the Ag + and C1 - ions in solution, so that the process expressed by the last equation is reversible:

Ag + + C1 - ↔ AgCl↓

However, due to the low solubility of silver chloride, this equilibrium is very strongly shifted to the right. Therefore, we can assume that the reaction of the formation of AgCl from ions is almost complete.

The formation of an AgCl precipitate will always be observed when there are significant concentrations of Ag + and C1 - ions in the same solution. Therefore, using silver ions, you can detect the presence of C1 - ions in a solution and, conversely, using chloride ions - the presence of silver ions; the C1 - ion can serve as a reagent for the Ag + ion, and the Ag + ion can serve as a reagent for the C1 ion.

In the future, we will widely use the ionic-molecular form of writing equations for reactions involving electrolytes.

To compose ion- molecular equations you need to know which salts are soluble in water and which are practically insoluble. general characteristics The solubility of the most important salts in water is given in Table 2.

Ionic-molecular equations help to understand the characteristics of reactions between electrolytes. Let us consider, as an example, several reactions occurring with the participation of weak acids and bases.

Table 2. Solubility of the most important salts in water

As already mentioned, the neutralization of any strong acid by any strong base is accompanied by the same thermal effect, since it comes down to the same process - the formation of water molecules from hydrogen ions and hydroxide ions. However, when neutralizing a strong acid with a weak base, or a weak acid with a strong or weak base, the thermal effects are different. Let's write ion-molecular equations for such reactions.

Neutralization of a weak acid (acetic acid) with a strong base (sodium hydroxide):

CH 3 COOH + NaOH = CH 3 COONa + H 2 O

Here the strong electrolytes are sodium hydroxide and the resulting salt, and the weak ones are acid and water:

CH 3 COOH + Na + + OH - = CH 3 COO - + Na + + H 2 O

As can be seen, only sodium ions do not undergo changes during the reaction. Therefore, the ion-molecular equation has the form:

CH 3 COOH + OH - = CH 3 COO - + H 2 O

Neutralization of a strong acid (nitrogen) with a weak base (ammonium hydroxide):

HNO 3 + NH 4 OH = NH 4 NO 3 + H 2 O

Here we must write the acid and the resulting salt in the form of ions, and ammonium hydroxide and water in the form of molecules:

H + + NO 3 - + NH 4 OH = NH 4 - + NH 3 - + H 2 O

NO 3 - ions do not undergo changes. Omitting them, we obtain the ionic-molecular equation:

H + + NH 4 OH= NH 4 + + H 2 O

Neutralization of a weak acid (acetic acid) with a weak base (ammonium hydroxide):

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

In this reaction, all substances, except the salt formed, are weak electrolytes. Therefore, the ion-molecular form of the equation looks like:

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

Comparing the obtained ion-molecular equations with each other, we see that they are all different. Therefore, it is clear that the heats of the reactions considered are also different.

Reactions of neutralization of strong acids with strong bases, during which hydrogen ions and hydroxide ions combine to form a water molecule, proceed almost to completion. Neutralization reactions, in which at least one of the starting substances is a weak electrolyte and in which molecules of weakly dissociating substances are present not only on the right, but also on the left side of the ion-molecular equation, do not proceed to completion. They reach a state of equilibrium in which the salt coexists with the acid and base from which it was formed. Therefore, it is more correct to write the equations of such reactions as reversible reactions:

CH 3 COOH + OH - ↔ CH 3 COO - + H 2 O

H + + NH 4 OH↔ NH 4 + + H 2 O

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

With other solvents, the considered patterns remain the same, but there are also deviations from them, for example, a minimum (anomalous electrical conductivity) is often observed on the λ-c curves. 2. Ion mobility Let us relate the electrical conductivity of an electrolyte to the speed of movement of its ions in an electric field. To calculate electrical conductivity, it is enough to count the number of ions...

When studying the synthesis of new materials and processes of ion transport in them. In their pure form, such patterns are most clearly visible in the study of single-crystal solid electrolytes. At the same time, when using solid electrolytes as working media for functional elements, it is necessary to take into account that materials of a given type and shape are needed, for example in the form of dense ceramics...

17-25 kg/t aluminum, which is ~ 10-15 kg/t higher compared to the results for sandy alumina. Alumina used for the production of aluminum must contain a minimum amount of compounds of iron, silicon, heavy metals with a lower potential for release at the cathode than aluminum, because they are easily reduced and converted into cathode aluminum. It is also undesirable to be present in...

Chemical properties acids and bases.

Chemical properties of BASES:

1. Effect on indicators: litmus - blue, methyl orange - yellow, phenolphthalein - crimson,
2. Base + acid = Salts + water Note: the reaction does not occur if both the acid and the alkali are weak. NaOH + HCl = NaCl + H2O
3. Alkali + acidic or amphoteric oxide = salts + water
2NaOH + SiO2 = Na2SiO3 + H2O
4. Alkali + salts = (new) base + (new) salt note: the starting substances must be in solution, and at least 1 of the reaction products must precipitate or dissolve slightly. Ba(OH)2 + Na2SO4 = BaSO4+ 2NaOH
5. Weak bases decompose when heated: Cu(OH)2+Q=CuO + H2O
6.When normal conditions it is impossible to obtain hydroxides of silver and mercury; instead, water and the corresponding oxide appear in the reaction: AgNO3 + 2NaOH(p) = NaNO3+Ag2O+H2O

Chemical properties of ACIDS:
Interaction with metal oxides to form salt and water:
CaO + 2HCl(diluted) = CaCl2 + H2O
Interaction amphoteric oxides with the formation of salt and water:
ZnO+2HNO3=ZnNO32+H2O
Interaction with alkalis to form salt and water (neutralization reaction):
NaOH + HCl(dil.) = NaCl + H2O
Reaction with insoluble bases to form salt and water, if the resulting salt is soluble:
CuOH2+H2SO4=CuSO4+2H2O
Interaction with salts, if precipitation occurs or gas is released:
Strong acids displace weaker ones from their salts:
K3PO4+3HCl=3KCl+H3PO4
Na2CO3 + 2HCl(diluted) = 2NaCl + CO2 + H2O
Metals that are in the activity series before hydrogen displace it from the acid solution (except for nitric acid HNO3 of any concentration and concentrated sulfuric acid H2SO4), if the resulting salt is soluble:
Mg + 2HCl(dil.) = MgCl2 + H2
With nitric acid and concentrated sulfuric acids the reaction proceeds differently:
Mg + 2H2SO4 = MgSO4 + 2H2O + SO4
Organic acids are characterized by an esterification reaction (reaction with alcohols to form an ester and water):
CH3COOH + C2H5OH = CH3COOC2H5 + H2O

Nomenclature and chemical properties of salts.

Chemical properties of SALT
They are determined by the properties of the cations and anions included in their composition.

Salts interact with acids and bases if the reaction results in a product that leaves the reaction sphere (precipitate, gas, slightly dissociating substances, for example, water):
BaCl2(solid) + H2SO4(conc.) = BaSO4↓ + 2HCl
NaHCO3 + HCl(diluted) = NaCl + CO2 + H2O
Na2SiO3 + 2HCl(diluted) = SiO2↓ + 2NaCl + H2O
Salts interact with metals if the free metal is to the left of the metal in the salt in the electrochemical series of metal activity:
Cu+HgCl2=CuCl2+Hg
Salts interact with each other if the reaction product leaves the reaction sphere; including these reactions can take place with a change in the oxidation states of the reactant atoms:
CaCl2 + Na2CO3 = CaCO3↓ + 2NaCl
NaCl(dil.) + AgNO3 = NaNO3 +AgCl↓
3Na2SO3 + 4H2SO4(dil.) + K2Cr2O7 = 3Na2SO4 + Cr2(SO4)3 + 4H2O + K2SO4
Some salts decompose when heated:
CuCO3=CuO+CO2
NH4NO3 = N2O + 2H2O
NH4NO2 = N2 + 2H2O

Complex compounds: nomenclature, composition and chemical properties.

Ion exchange reactions involving precipitation and gases.

Molecular and molecular-ionic equations.

These are reactions that occur in solutions between ions. Their essence is expressed by ionic equations, which are written as follows:
strong electrolytes are written in the form of ions, and weak electrolytes, gases, precipitates (solids) are written in the form of molecules, regardless of whether they are on the left or right side of the equation.

1. AgNO 3 + HCl = AgCl↓ + HNO 3 – molecular equation;
Ag + + NO 3 – + H + + Cl – = AgCl↓ + H + + NO 3 – – ionic equation.

If the identical ions on both sides of the equation are canceled out, the resulting shortened, or abbreviated, ionic equation is:

Ag + + Cl – = AgCl↓.

CaCO 3 ↓ + 2H + + 2Cl – = Ca 2+ + Cl – + CO 2 + H 2 O,
CaCO 3 ↓ + 2H + = Ca 2+ + CO 2 + H 2 O.

4. CH 3 COOH + NH 4 OH = CH 3 COONH 4 + H 2 O,
CH 3 COOH + NH 4 OH = CH 3 COO – + NH 4 + +H 2 O,
CH 3 COOH and NH 4 OH are weak electrolytes.

CH 3 COO – +NH 4 + + Na + + OH – = CH 3 COO – + Na + + NH 3 + H 2 O,
CH 3 COO – + NH 4 + + OH – = CH3COO – + NH 3 + H 2 O.

Reactions in electrolyte solutions proceed almost to completion towards the formation of precipitation, gases and weak electrolytes.

4.2) The molecular equation is a common equation that we often use in class.
For example: NaOH+HCl -> NaCl+H2O
CuO+H2SO4 -> CuSO4+H2O
H2SO4+2KOH -> K2SO4+2H2O, etc.
Ionic equation.
Some substances dissolve in water, forming ions. These substances can be written using ions. And we leave those that are slightly soluble or difficult to dissolve in their original form. This is the ionic equation.
For example: 1) CaCl2+Na2CO3 -> NaCl+CaCO3 molecular equation
Ca+2Cl+2Na+CO3 -> Na+Cl+CaCO3-ion equation
Cl and Na remained the same as they were before the reaction, the so-called. they did not take part in it. And they can be removed from both the right and left sides of the equation. Then it turns out:
Ca+CO3 -> CaCO3
2) NaOH+HCl -> NaCl+H2O-molecular equation
Na+OH+H+Cl -> Na+Cl+H2O ionic equation
Na and Cl remained the same as they were before the reaction, the so-called. they did not take part in it. And they can be removed from both the right and left sides of the equation. Then it works?
OH+H -> H2O