How to Write a net ionic equation

The net ionic equation is an important part of chemistry because it represents only the elements that are changed in a chemical reaction. They are most commonly used in oxidation-reduction reactions, exchange reactions, and acid-base neutralization reactions. ^{[1] X Research Source} There are three basic steps to writing a net ionic equation: balancing the molecular equation, converting it to a full ionic equation (according to how each substance exists in solution), and finally Write the net ionic equation.

Table of Contents

Learn the components of the ionic equation

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Know the difference between molecule and ionic compound . The first step in writing a net ionic equation is to identify the ionic compounds in the reaction. Ionic compounds are substances that dissociate into ions in aqueous solution and have an electrical charge. ^{[2] X Research Source} Molecular compounds are compounds that never have an electrical charge. They are formed between two nonmetals and are sometimes called covalent compounds. ^{[3] X Research Sources}

Ionic compounds can be formed between metals and nonmetals, metals and polyatomic ions, or many polyatomic ions.
If you’re not sure what a compound it is, you can find the elements in that compound on the periodic table. ^{[4] X Research Sources}

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Determine the solubility of a compound. Not all ionic compounds are soluble in aqueous solutions, and therefore cannot dissociate into ions. You must know the solubility of each compound before proceeding to the rest of the equation. Here is a summary of the rules of solubility. Find a tan worksheet for more detailed information and to know the exceptions to these rules. ^{[5] X Research Sources}

Implement these rules in the order outlined below:
All salts Na ⁺ , K ⁺ , and NH ₄⁺ are soluble.
All salts NO ₃^– , C ₂ H ₃ O ₂^– , ClO ₃^– , and ClO ₄^– are soluble.
All salts Ag ⁺ , Pb ²⁺ , and Hg ₂²⁺ are soluble.
All salts Cl ^– , Br ^– , and I ^– are soluble.
All salts CO ₃^2- , O ^2- , S ^2- , OH ^– , PO ₄^3- , CrO ₄^2- , Cr ₂ O ₇^2- , and SO ₃^2- are soluble (with a few exceptions). .
All SO ₄^2- salts are soluble (except in a few cases).

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Identify cations and anions in compounds. A cation is a positive ion in a compound and is usually a metal. Anions are negative ions in compounds and are nonmetals. Some nonmetals can form cations but metals always form cations. ^{[6] X Research Source}

For example, in NaCl, Na is the positively charged cation because it is a metal, and Cl is the negatively charged anion because it is a nonmetal.

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Identify polyatomic ions in the reaction. Polyatomic ions are electrically charged molecules that are tightly bound together and do not dissociate in chemical reactions. ^{[7] X Source of Study} It is important to recognize polyatomic ions because they have their own charge and do not dissociate. Polyatomic ions can carry a positive or negative charge.

If you are studying general chemistry it is often asked to memorize some common polyatomic ions.
Some common polyatomic ions are CO ₃^2- , NO ₃^– , NO ₂^– , SO ₄^2- , SO ₃^2- , ClO ₄^– and ClO ₃^– . ^{[8] X Research Sources}
Also you can find many other ions in chemistry books or on the internet. ^{[9] X Research Source}

Write the net ionic equation

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Balance the molecular equation. Before writing the net ionic equation, you must make sure that the molecular equation is balanced. To balance the equation, you add a coefficient in front of the compound so that the number of atoms of each element is equal on both sides of the equation.

Write the number of atoms that form each compound on both sides of the equation.
Add coefficients before elements other than oxygen and hydrogen to balance each side.
Hydrogen atom balance.
Oxygen atom balance.
Count the number of atoms on each side of the equation to make sure they are balanced.
For example, Cr + NiCl ₂ –> CrCl ₃ + Ni is balanced to 2Cr + 3NiCl ₂ –> 2CrCl ₃ + 3Ni.

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Identify the state of the compound in the equation. Sometimes in the problem there are keywords so that you know the state of each compound. There are several rules that help determine the state of an element or compound. ^{[10] X Research Source}

If the state of the element is not provided, use the state found on the periodic table.
If the compound is called a solution, you can write it as aqueous or ( dd ).
If there is water in the equation, you must determine if the ionic compound is water soluble by using the solubility worksheet. ^{[11] X Research Source} If the solubility is high, the compound will be in the aqueous state ( dd ), if the solubility is low, the compound will be in the solid state ( r ).
In the absence of water, the ionic compound is solid ( r ).
If the problem is written as an acid or a base, then the compound is aqueous ( dd ).
For example, 2Cr + 3NiCl ₂ –> 2CrCl ₃ + 3Ni. Elemental forms of Cr and Ni are in the solid state. NiCl ₂ and CrCl ₃ are ionic compounds, so they are aqueous. Rewrite the equation as: 2Cr _{( r )} + 3NiCl _{2( dd )} –> 2CrCl _{3( dd )} + 3Ni _{( r )} .

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Determine which compounds will dissociate (dissociate into cations and anions) in solution. When a substance or compound dissociates, it dissociates into positively charged ions (cations) and negatively charged ions (anions). These are the final balanced components of the net ionic equation.

Solids, liquids, gases, molecular compounds, ionic compounds with low solubility, polyatomic ions and weak acids will not dissociate.
Ionic compounds with high solubility (use solubility worksheet) and strong acids will ionize 100% (HCl _{( dd )} , HBr _{( dd )} , HI _{( dd )} , H ₂ SO _{4( dd )} , HClO _{4( dd ) )} , and HNO _{3( dd )} ). ^{[12] X Research Source}
Note, although polyatomic ions do not dissociate further, if they are constituents of the compound they will dissociate from the compound.

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Calculate the charge of each ion dissociated from the compound. Remember that metals will form positive ions and nonmetals will form negative ions. Use the periodic table to determine the charge of the element. You also have to balance the charge of each ion in the compound.

In this example, NiCl ₂ dissociates into Ni ²⁺ and Cl ^– while CrCl ₃ dissociates into Cr ³⁺ and Cl ^– .
Ni has a charge of 2+ because Cl has a charge of negative one but has 2 atoms. So we have to balance 2 negative Cl ions. Cr has a charge of 3+, so we have to balance 3 negative Cl ions.
Remember that polyatomic ions have a charge of their own. ^{[13] X Research Source}

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Write the complete ionic equation. Anything that dissociates or ionizes (strong acid) dissociates into two separate ions. The state of the substance is still ( dd ), but you have to make sure the equation is still in balance.

Solids, liquids, gases, weak acids and ionic compounds with low solubility do not change state or separate into ions. We keep these substances intact.
The molecules will be dispersed in solution so their state will change to ( dd ). The three exceptions that don’t become ( dd ) are: CH _{4( k )} , C ₃ H _{8( k )} , and C ₈ H _{18( l )} .
Continuing with the above example, the full ionic equation would look like this: 2Cr _{( r )} + 3Ni ²⁺_{( dd )} + 6Cl ^–_{( dd )} –> 2Cr ³⁺_{( dd )} + 6Cl ^–_{( dd )} + 3Ni _{( r )} . When Cl is not present in the compound, it is not a diatomic substance, so we multiply the factor by the number of atoms in the compound to get 6 Cl ions on both sides of the equation.

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Eliminate the equilibrium ion by suppressing the same ions on each side of the equation. You can only cancel if they are exactly the same on both sides (charge, atomic number, etc.). Rewrite the equation without the substances that have been suppressed.

After completing the example, we have 6 equilibrium Cl ions ^– cancelable on each side. The net ionic equation is 2Cr _{( r )} + 3Ni ²⁺_{( dd )} –> 2Cr ³⁺_{( dd )} + 3Ni _{( r )} .
If you write it correctly then the total charge on the reactant side should be equal to the total charge on the product side in the net ionic equation.

Advice

Write the states of all substances in the equation, otherwise you will lose points.

Steps

Learn the components of the ionic equation

Write the net ionic equation

Advice

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