Key points and precautions for writing ion equations

How to Write Chemical Equations.

1. It is necessary to follow the reaction facts, and no chemical reactions can be fabricated.

2. It is necessary to follow the conservation of atomic atoms and charge of elements, and if it is a redox reaction, it is necessary to follow the conservation of electrons.

Dismantling principles should be followed (reactants and products are the same).

The principle of simplicity cannot be violated.

Pay attention to the relationship between the quantities in the question (e.g., excess, sufficient, small amount).

Basic steps. 1. Writing: Clearly write the chemical equation about the reaction.

2. Dismantling: Soluble strong electrolytes (strong acids, strong bases, soluble salts) are all represented by ion symbols, and other insoluble substances. Substances that are difficult to ionize, gases, oxides, water, etc., are still expressed by chemical formulas.

For microsoluble substances, they are usually present in ionic form (in solution) in ionic reactions, but in turbid liquids, the complete chemical formula needs to be written.

3. Delete: Delete the same ions and molecules on both sides of the equation.

4. Check: Check whether the number of atoms and the number of charges on both sides of the formula are equal and balanced, and whether the stoichiometric number of the obtained formula is the simplest integer ratio, if not, it should be reduced to the simplest integer ratio.

The basic steps for writing an ionic equation are:

Write": Write the chemical equation about the reaction.

Dismantling": Soluble strong electrolytes (strong acids, strong bases, soluble salts) are represented by ion symbols, and other insoluble substances, gases, water, etc. are still expressed by molecular formulas. Slightly soluble strong electrolytes should be seen to see if they exist mainly in the form of free ions, e.g., Ca(OH)2 in lime water is represented by ionic symbols, and Ca(OH)2 in lime milk is expressed by molecular formulas.

Due to the presence of mainly sulfuric acid molecules, the chemical formula is also written. Concentrated nitric acid and hydrochloric acid are written as ionic formulas.

Delete": Remove ions on both sides of the equation that do not participate in the reaction.

Check": Check whether the number of atoms and the number of charges on both sides of the formula are equal (to see whether they are balanced), and also see whether the obtained stoichiometric number of the formula is the simplest integer ratio, if not, it should be reduced to the simplest integer ratio.

There are six things to look at when judging whether the ion equation is correct or not

First, whether it conforms to objective facts;

Second, see whether the chemical formula or ion symbol representing each substance is correct;

Third, look at the conservation of charge and the conservation of mass;

Fourth, see if the reaction is omitted;

Fifth, see whether the ratio of reactants or products is correct;

Sixth, see whether the "long equal sign", "reversible number", "gas number" and "precipitation number" are correct.

Error-prone analysis of this paragraph:

All oxide peroxides are written in a unified chemical formula, and beginners are easy to ignore, and only soluble and easily ionized electrolytes are represented by ion symbols, which often disassemble many insoluble strong electrolytes, resulting in errors. It must be clear here that active metal oxides like sodium peroxide, sodium oxide, etc., or peroxides, although soluble electrolytes.

There are also strong soluble electrolytes like sodium bicarbonate, but sometimes (e.g. carbon dioxide into saturated sodium carbonate) is also written as a chemical formula, depending on whether it is mainly in the form of a solid substance or in the form of ions in solution.

Acid salts of strong acids, such as sodium bisulfate, should be divided into sodium ions, hydrogen ions and sulfate ions (only bisulfate belongs to this category in high schools); Weakly acid acid salts such as sodium bicarbonate are split into sodium ions and carbonic acid ions (acid salts such as carbonic acid, phosphoric acid, sulfurous acid, etc. are all of this type).

Weak electrolytes, non-electrolytes, oxides, elemental matter, precipitation, and gases cannot be disassembled.

The rules for writing the ion equation are as follows:

1. Common types of ionic reactions:

1. Metathesis ion reaction: e.g. AG++Cl-=AGCL 2H++CO32-=CO2 +H2O

2. Replacement reaction type: e.g. Zn+2H+=Zn2++H2 Cl2+2I-=2Cl-+I2

3. Salt hydrolysis type: e.g.: NH4 H2O==NH3·H2O+H+CH3COO-+H2O==CH3COOH+0H-

4. Complex oxidation reduction: e.g., MNO4-+5Fe2++8H+=5Fe3++Mn2++4H2O

In addition, there are ionic reactions when there is a complex in the product.

Example 1: A small amount of Cl2 is passed into an aqueous solution of H2S: Cl2+H2S S 2H++2Cl-, and an excess of Cl2 is passed into an aqueous solution of H2S: 4Cl2+H2S+4H2O 10H++SO42-+8Cl-

Example 2: Ca(HCO3)2 solution with an appropriate amount or excess of NaOH solution: Ca2++2HCO3-+2OH-=CaCO3 +CO3-+2H2O If it acts with a small amount of NaOH solution, it should be written:

ca2++hco3-+oh-=caco3↓+h2o

Example 3: Interaction of clarified lime water with excess NaHCO3 solution: the same formula 2 and a small amount of NaHCO3 solution are the same as Example 2.

Example 4: Add an excess of Ca(OH)2 solution dropwise to Ca(H2PO4)2 solution: 3Ca2++2H2PO4-+4OH-=Ca3(PO4)2 +4H2O Add a small amount of Ca(OH)2 solution dropwise to Ca(H2PO4)2 solution:

ca2++h2po4-+oh-＝cahpo4↓+h2o

Example 5: Add Ba(OH)2 solution dropwise to NaHSO4 solution until the precipitate is exactly complete H++SO42-+BA2++OH-=BASO4 +H2O Add BA(OH)2 solution dropwise to NaHSO4 solution until the precipitate is exactly neutralized: 2H++SO42-+Ba2++2OH-=BASO4 +2H2O Rule:

When the positive and negative ions of an electrolyte fully participate in the reaction, the ratio of the number of positive and negative ions in the reactant should be the same as the composition ratio of the electrolyte in the balanced ion equation. When the positive and negative ions of an electrolyte are both reactive but not completely reacted, the individual number ratios of the positive and negative ions are not the same as their electrolyte composition in the balanced ion equation.

The ion equation is an equation used to express the formation and disappearance of ions in a chemical reaction. Here are the rules for writing the ion equation:

Breaking reactants and products into ions: Splitting compounds in a chemical formula into their ionic forms.

Write the charge of the ion: Add a charge symbol (e.g., + or -) to the top right of the ion to indicate its charge.

Balanced Charge: Ensure that the positive and negative charges are equal in the ionic equation to maintain the charge balance.

Write the phase state: Use the symbols (s), (l), (g), (aq) to indicate the state of solids, liquids, gases, and solutions, where (aq) indicates the aqueous solution. For example, NaCl (AQ) indicates that sodium chloride dissolves in water.

Eliminate ions that are involved in the reaction but do not change: Some ions do not change in the reaction and can be omitted from the equation.

Chemical Equation Equilibrium: Make sure that the number of each ion in the ion equation is balanced on the reactant side and the product side. The ion equation only applies to ionic reactions in solution, not to gases and solids.

In gas and solid reactions, molecular equations are often used to represent chemical reactions.

The ionic equation is a representation used to describe the formation and disappearance of ions in a chemical reaction. The ion equation reveals more accurately the participation and change of ions in a chemical reaction by breaking down chemical substances into the form of ions.

In general chemical equations, we use chemical formulas and state symbols to represent the chemical changes between reactants and products. However, this equation does not provide detailed information about the pairing and conversion between ions. To better describe the ionic reactions that occur in an aqueous solution, the ionic equation breaks down chemical species into their ionic forms and clearly indicates the formation and disappearance of ions.