Advice 1: How to solve ionic equations

In solutions of electrolytes reactions occur between the ions therefore they are called ionic reactions, or reactions of ion exchange. They are described by ionic equations. Compounds that are sparingly soluble, or volatile multicolinearity, write in molecular form. If the interaction of solutions of electrolytes is not formed any of these types of connections, this means that the reaction almost does not occur.
How to solve ionic equations
Consider the example of formation of soluble compounds.

Na2SO4 + BaCl2 = BaSO4 + 2NaCl

Or in ionic form:

2Na+ +SO42- +Ba2++ 2Cl- = BaSO4 + 2Na+ + 2Cl-
Please note that reacted only barium ions and sulfate ions, as other ions has not changed, therefore this equation can be written in abbreviated form:

Ba2+ + SO42- = BaSO4
When solving ionic equations, you must observe the following rules:

the same ions from both parts are excluded;

- it should be remembered that the amount of electric charges in the left side of the equation must equal the sum of the electric charges in the right part of the equation.

To write ionic equations of the reactions of interaction between aqueous solutions of the following substances: a) HCl and NaOH; b) AgNO3 and NaCl; C) К2СО3 and H2SO4; d) CH3COOH and NaOH.

Solution. Write down the equations of the interaction of these substances in molecular form:

a) HCl + NaOH = NaCl + H2O

b) AgNO3 + NaCl = AgCl + NaNO3

C) K2CO3 + H2SO4 = K2SO4 + CO2 + H2O

d) CH3COOH + NaOH = CH3COONa + H2O
Note that the interaction of these substances is possible because the result is the binding of ions with the formation of either a weak electrolyte (H2O) or soluble substances (AgCl), or gas (CO2).
In the case of variant d), the reaction goes in the direction of greater binding of ions, i.e. the formation of water, although there are two weak electrolyte (acetic acid and water). But this happens because water is a weak electrolyte.
Excluding the same ions from the left and right parts of equality (in the case of option (a) ions of sodium and chlorine, in case b) is the sodium ions and nitrate ions, in the case of C) ions of potassium and sulfate ions), g) – sodium ions, get the solution of these ionic equations:

a) H+ + OH- = H2O

b) Ag+ + Cl- = AgCl

C) CO32- + 2H+ = CO2 + H2O

d) CH3COOH + OH- = CH3COO- + H2O

Advice 2 : How to write a molecular equation for the reaction

Chemical reactions, that is, interactions of substances, which are accompanied by changes in their composition, can be described as molecular equations. Some question may arise: how to make this molecular equation?
How to write a molecular equation for the reaction
The reaction should be possible, i.e. its flow acceptable from the point of view of known physical and chemical laws. For example:
Zn + 2HCl = ZnCl2 + H2 this reaction between zinc and hydrochloric acid possible;

2Au + 6HCl = 2AuCl3 + 3H2 - but the reaction between gold and hydrochloric acid is impossible, though, zinc and gold metals. The reason is the location of zinc and gold in the "electrochemical series of the stress". Zinc is much more to the left of hydrogen, and gold, respectively, far right.
In the left part of equations the formulas of the substances entering into the reaction (original substance), and on the right side of the equation – formulas of substances, the resulting reaction (the"products").
Although we are talking about the equations we must firmly remember that the mathematical rule "From change of places composed the sum does not change" does not apply here. In other words, in the molecular equation of a chemical reaction in any case you can not swap left and right part. This will change its meaning. For example:
AgNO3 + KBr = KNO3 + AgBr (precipitate), reaction in this form, you can write, it flows to the end, is formed as a slightly soluble substance – bromide of silver;

AgBr + KNO3 = AgNO3 + KBr - but in this form (although you only swapped the left and right sides) it will not go.
The coefficients must be selected so that the number of atoms of any element in the left and right sides was the same. For example:
Na2SO4 + 2BaCl = 2NaCl + BaSO4.
It is easy to verify that in the left and right side of the equation contains two sodium atoms, four atoms of oxygen, two atoms of barium, two atoms of chlorine and one atom of sulfur.
To make it easier to make a molecular equation reactions, one should immediately remember this simple rule: the reaction goes to end, if at least one of the reaction products leaving the reaction zone, that is, escapes in the form of a gas or precipitate, if it is a slightly soluble substance. For example:
H2SO4 + Na2CO3 = Na2SO4 + H2CO3.
The resulting carbonic acid (Н2СО3) is so unstable that almost instantly decomposes into carbon dioxide and water. Therefore, the reaction can immediately write in the final form:
H2SO4 + Na2CO3 = Na2SO4 + H2O + CO2.

Advice 3 : How to write the equation in the molecular and molecular-ionic forms

A chemical equation is a record made in accordance with the rules. It describes reactions, that is, describes what substances took part in it and what was formed. The equation can be written in full form (molecular) and condensed (ion).
How to write the equation in the molecular and molecular-ionic forms
In the left side of the equation write down the substances entering into a chemical reaction. They are called "original substances". On the right side, respectively, of the resulting substances ( "reaction products").
When writing formulas for molecules use chemical symbols of common atoms. The index of each atom is determined by the formula of the compound and valence.
Remember that unlike mathematical equations, the equations of chemical reactions in any case it is impossible to swap the right and left parts! Because it completely changes the meaning of the record. In addition, this reaction is often simply impossible.
The number of atoms of all elements in the left and right side of the reaction must be the same. If necessary, the "trim" number produced by the selection of coefficients.
When writing equations chemical reactions first make sure that it is at all possible. That is, that its occurrence does not contradict to the known physico-chemical rules and properties of substances. For example, the reaction:

NaI + AgNO3 = NaNO3 + AgI
She proceeds quickly to the end, in the course of the reaction forms insoluble light yellow precipitate of silver iodide. And the reverse reaction:

AgI + NaNO3 = AgNO3 + NaI - impossible, though, and recorded the correct symbols, and the number of atoms of all elements in the left and right sides the same way.
Write down the equation in the "full" form, that is, using their molecular formula. For example, the reaction form a precipitate of barium sulfate:

BaCl2 + Na2SO4 = 2NaCl + BaSO4
But can the same reaction be written in ionic form:

Ba 2+ + 2Cl- + 2Na+ + SO4 2- = 2Na+ + 2Cl- + BaSO4
You see that in the left and right parts of the equations contain exactly the same ions of chlorine and sodium. Discard them and get final abbreviated equation of the reaction in ionic form:

Ba 2+ + SO4 2- = BaSO4
Similarly, you can write in ionic form the equation for another reaction. Remember that each molecule soluble (dissociated) substances are written as ions, the same ions in the left and right side of the equation are eliminated.

Advice 4 : How to write ionic equations

From the point of view of the theory of electrolytic dissociation, the solutions of some compounds can conduct electric current, as the decay on the positive and negative particles – ions. Such substances are called electrolytes, which include salt, acids, bases. Most chemical reactions proceeds in solutions, and therefore between the ions, because you need to know how to write ionic equations.
How to write ionic equations
You will need
  • - table of solubility of salts, acids, bases.
Before you start writing ionic equations, you must learn some rules. Insoluble in water, gaseous and multiscaleimage substances (e.g., water) into ions does not decay, and hence write them in molecular form. Also included is the weak electrolytes, such as H2S, H2CO3, H2SO3, and NH4OH. The solubility of compounds can be found on the table of solubility, which is allowed reference material on all types of control. There are all the charges that are inherent in the cations and anions. For the full job, you need to write molecular, ionic full and abbreviated ion equations.
Example No. 1. Write the neutralization reaction between sulfuric acid and potassium hydroxide, look at it from the point of view of TED (of the theory of electrolytic dissociation). First, write the reaction equation in molecular form and set up the coefficients.H2SO4 + 2KOH = K2SO4 + 2Н2ОПроанализируйте derived substances for their solubility and dissociation. All connections are water-soluble and therefore dissociate into ions. The exception is water, which does not break up into ions, therefore, will remain in molecular form.Write the complete ionic equation, find the same ions in the left and right sides and emphasize. To reduce the same ions strike them.2H+ +SO4 2- +2K+ +2OH- = 2K+ +SO4 2- + 2Н2ОВ the result is a short ionic equation:2H+ +2OH- = 2Н2ОКоэффициенты in twos can also be reduced:H+ +OH- = H2O
How to write ionic <strong>equation</strong>
Example No. 2. Write the exchange reaction between copper chloride and sodium hydroxide, look at it from the point of view of TED. Write down the reaction equation in molecular form and set up the coefficients. As a result, the formed copper hydroxide precipitate blue. CuCl2 + 2NaOH = Cu(OH) 2↓ +2NaClПроанализируйте all substances to their water solubility – soluble all except copper hydroxide, which on the ions to dissociate is not. Write the complete ionic equation, and emphasize and reduce the same ions:Cu2+ +2Cl- + 2Na+ +2OH- = Cu(OH) 2↓+2Na+ +2Cl-Remains short ion equation:Cu2+ +2OH- = Cu(OH) 2↓
How to write ionic <strong>equation</strong>
Example No. 3. Write the exchange reaction between sodium carbonate and hydrochloric acid, consider it from the point of view of TED. Write down the reaction equation in molecular form and set up the coefficients. The reaction produced sodium chloride, and is allocated gaseous substance CO2 (carbon dioxide or carbon oxide (IV)). It is formed by decomposition of carbonic acid is a weak, disintegrating to the oxide and water. Na2CO3 + 2HCl = 2NaCl + CO2↑+Н2ОПроанализируйте all substances for their solubility in water and dissociation. Carbon dioxide leaves the system as gaseous compound, water is madisoniorum substance. All the other substances break up into ions. Write the complete ionic equation, and emphasize and reduce the same ions:2Na+ +CO3 2- +2H+ +2Cl- =2Na+ +2Cl- +CO2↑+Н2ООстается short ionic equation:CO3 2- +2H+ =CO2↑+H2O
How to write ionic <strong>equation</strong>
To determine the number of ions, we need the coefficient before the formula, multiplied by the index.
Useful advice
In the reaction equation be sure to check the coefficients.
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