How to Write Total and Net Ionic Equations (Easy)




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How to Write a Net Ionic Equation

Two Parts:

Net ionic equations are an important aspect of chemistry as they represent only the entities that change in a chemical reaction. They are most commonly used in redox reactions, double replacement reactions, and acid-base neutralisations.There are three basic steps to writing a net ionic equation: balancing the molecular equation, transforming to a complete ionic equation (how each species exists in solution), and then writing the net ionic equation.

Steps

Understanding the Components of an Ionic Equation

  1. Know the difference between molecular and ionic compounds.The first step in writing a net ionic equation is identifying the ionic compounds of the reaction. Ionic compounds are those that will ionize in an aqueous solution and have a charge.Molecular compounds are compounds that never have a charge. They are made between two non-metals and are sometimes referred to as covalent compounds.
    • Ionic compounds can be between metals and nonmetals, metals and polyatomic ions, or multiple polyatomic ions.
    • If you are unsure of a compound, look up the elements of the compound on the periodic table.
    • Net ionic equations apply to reactions involving strong electrolytes in water.
  2. Identify the solubility of a compound.Not all ionic compounds are soluble in an aqueous solution and therefore, will not dissociate into individual ions. You must identify the solubility of each compound before proceeding with the rest of the equation. Below is a brief summary of the rules of solubility. Seek out a solubility chart for more details and exceptions to these rules.
    • Follow these rules in the order stated below:
    • All Na+, K+, and NH4+salts are soluble.
    • All NO3-, C2H3O2-, ClO3-, and ClO4-salts are soluble.
    • All Ag+, Pb2+, and Hg22+salts are insoluble.
    • All Cl-, Br-, and I-salts are soluble.
    • All CO32-, O2-, S2-, OH-, PO43-, CrO42-, Cr2O72-, and SO32-salts are insoluble (with some exceptions).
    • All SO42-salts are soluble (with some exceptions).
  3. Determine the cation and anion in a compound.Cations are the positive ions in a compound and are generally the metals. Anions are the negative, non-metal ions in the compound. Some non-metals are capable of forming cations, but metals will always form cations.
    • For example, in NaCl, Na is the positively charged cation because it is a metal while Cl is the negatively charged anion because it is a non-metal.
  4. Recognize polyatomic ions in the reaction.Polyatomic ions are charged molecules that are bound so tightly together that they do not dissociate during chemical reactions.It is important to recognize polyatomic ions as they have a specific charge and do not break down into their individual components. Polyatomic ions can be both positively and negatively charged.
    • If you are in a standard chemistry course, you will likely be expected to memorize some of the most common polyatomic ions.
    • Some common polyatomic ions include CO32-, NO3-, NO2-, SO42-, SO32-, ClO4-, and ClO3-.
    • There are many more and can be found in tables in your chemistry book or online.

Writing a Net Ionic Equation

  1. Balance the complete molecular equation.Before writing a net ionic equation, you must first make sure your starting equation is completely balanced. To balance an equation, you add coefficients in front of compounds until there is an equal number of atoms for each element on both sides of the equation.
    • Write the number of atoms that comprise each compound on either side of the equation.
    • Add a coefficient in front of elements that are not oxygen and hydrogen to balance each side.
    • Balance the hydrogen atoms.
    • Balance the oxygen atoms.
    • Re-count the number of atoms on each side of the equation to make sure they are equal.
    • For example, Cr + NiCl2--> CrCl3+ Ni becomes 2Cr + 3NiCl2--> 2CrCl3+ 3Ni.
  2. Identify the states of matter of each compound in the equation.Oftentimes, you will be able to identify keywords in a problem that will tell you the state of matter for each compound. There are some rules to help you determine the state of an element or compound.
    • If no state is provided for an element, use the state found on the periodic table.
    • If a compound is said to be a solution, you can write it as aqueous, or (aq).
    • If there is water in the equation, determine whether or not the ionic compound will dissolve using a solubility table.If it has high solubility, the compound will be aqueous (aq), if it has low solubility, it will be solid (s).
    • If there is not water, the ionic compound is a solid (s).
    • If the problem mentions an acid or a base, they will be aqueous (aq).
    • For example, 2Cr + 3NiCl2--> 2CrCl3+ 3Ni. Cr and Ni in their elemental forms are solids. NiCl2and CrCl3are soluble ionic compounds, therefore, they are aqueous. Rewritten, this equation becomes: 2Cr(s)+ 3NiCl2(aq)--> 2CrCl3(aq)+ 3Ni(s).
  3. Determine what species will dissociate (separate into cations and anions) in solution.When a species or compound dissociates, it separates into its positive (cation) and negative (anion) components. These will be the components that get balanced at the end for the net ionic equation.
    • Solids, liquids, gases, molecular compounds, low solubility ionic compounds, polyatomic ions, and weak acids will not dissociate.
    • The oxides and hydroxides with alkali or alkaline earth metals will dissociate completely.
    • High solubility ionic compounds (use solubility table) and strong acids will ionize 100% (HCl(aq), HBr(aq), HI(aq), H2SO4(aq), HClO4(aq), and HNO3(aq)).
    • Keep in mind, although polyatomic ions do not dissociate further, if they are a component of an ionic compound they will dissociate from that compound.
  4. Calculate the charge of each dissociated ion.Remember that metals will be the positive cation, while non-metals will be the negative anion. Using the group number on the periodic table to determine which element will have which charge. You must also balance the charges of each ion within the compound.
    • In our example, NiCl2dissociates into Ni2+and Cl-while CrCl3dissociates into Cr3+and Cl-.
    • Ni has 2+ charge because Cl has a minus charge, but there are 2 atoms of it. Therefore, it must balance the 2 negative Cl ions. Cr has a 3+ charge because it must balance the 3 negative Cl ions.
    • Remember that polyatomic ions have their own specific charge.
  5. Re-write the equation with the soluble ionic compounds broken down into their individual ions.Anything that will dissociate or ionize (strong acids) will simply separate into its two distinct ions. The state of matter will remain (aq), but you must ensure the equation remains balanced.
    • Solids, liquids, gasses, weak acids, and low solubility ionic compounds will not change state or separate into ions. Simply leave them as they are.
    • Molecular substances will simply disperse in solution, so their state will change to (aq). Three exceptions that donotbecome (aq) are: CH4(g), C3H8(g), and C8H18(l).
    • Continuing our example, the total ionic equation looks like this: 2Cr(s)+ 3Ni2+(aq)+ 6Cl-(aq)--> 2Cr3+(aq)+ 6Cl-(aq)+ 3Ni(s). When Cl is not in a compound, it is not diatomic; therefore, we multiplied the coefficient by the number of atoms in the compound to get 6 Cl ions on both sides of the equation.
  6. Remove the spectator ions by canceling out identical ions on each side of the equation.You can cancel only if they are 100% identical on both sides (charges, subscripts, etc.). Rewrite the action without any of the canceled species.
    • Spectator ions do not participate in the reaction, but they are present.
    • Finishing the example, there are 6Cl-spectator ions on each side that can be canceled out. The final net ionic equation is 2Cr(s)+ 3Ni2+(aq)--> 2Cr3+(aq)+ 3Ni(s).
    • To do a check to see if your answer works, the total charge on the reactant side should equal the total charge on the product side in the net ionic equation.

Community Q&A

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  • Question
    How to know the charge on the compound when an acid is dissociated in water such as H3PO4 in different steps?

    Ph.D. candidate in Health Sciences
    Meredith Juncker is a Ph.D. candidate in Health Sciences at Louisiana State University.
    Ph.D. candidate in Health Sciences
    Expert Answer
    H3PO4 is a triprotic acid, meaning it can undergo three dissociations and as such will have three dissociation constants (Ka1, Ka2, Ka3). So the charge on H3PO4 will change as each hydrogen ion dissociates in solution.
    Thanks!
  • Question
    Net ionic equation for zinc sulfide and hydrochloric acid

    Ph.D. candidate in Health Sciences
    Meredith Juncker is a Ph.D. candidate in Health Sciences at Louisiana State University.
    Ph.D. candidate in Health Sciences
    Expert Answer
    This is a double-displacement reaction with ZnCl2 and H2S as products. ZnS(aq) + 2HCl(aq) --> ZnCl2(aq) + 2H2S(g) The net ionic equation is: 2H+ + S2- --> 2H2S
    Thanks!
  • Question
    Why can't weak acids dissociate?
    wikiHow Contributor
    Community Answer
    Weak acids do dissociate but minimally because of their very low solubility. Their solubility is usually written as >50%.
    Thanks!
  • Question
    How do I write a net ionic equation if I'm not told whether it's a solid, liquid, or aqueous solution?
    wikiHow Contributor
    Community Answer
    Look at the periodic table and use whatever state it's in there, whether it's solid, liquid, or aqueous.
    Thanks!
  • Question
    How do I figure out how many ions are in a mole?
    wikiHow Contributor
    Community Answer
    There are 6.02X10^23 particles of anything in a mole. A mole of atoms is 6.02X10^23 atoms and a mole of molecules is 6.02X10^23 molecules.
    Thanks!
  • Question
    3SO2+ Cr2O7(2-)+2H(1+)----3SO4(2-)+2Cr(3+)+H20 Is this a correct ionic equation?
    wikiHow Contributor
    Community Answer
    No, sorry. That is a Doric Equation. You can tell by the fluting in the columns.
    Thanks!
  • Question
    How do I write the product of a chemical equation when I only know the reactants?
    wikiHow Contributor
    Community Answer
    it depends if it is a formation, single replacement, double replacement, or combustion.
    Thanks!
  • Question
    What is the simple way to balance net ionic equation?
    wikiHow Contributor
    Community Answer
    If you have the entire equation balanced, then just keep the coefficients and it balanced.
    Thanks!
  • Question
    How do I balance an equation with brackets?
    Ivy Park
    Community Answer
    Just think of the formula as the ones that you would see in your math class. When there is a bracket between numbers, you multiply them. Multiply the number in front of the formula and inside the bracket to get the number of that atom/molecule.
    Thanks!
Unanswered Questions
  • What's the ion equation for h2so4+ba(oh)2=baso4+h2o?
  • Can you provide some examples of ionic equations?
  • What is an easy way to remember the polymerizations?
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Basic guide to writing net ionic equations.

Quick Summary

To write a net ionic equation, first balance your starting equation. Then, identify the states of matter of each compound and determine what species will dissociate in solution. Next, calculate the charge of each dissociated ion and rewrite the equation with the soluble ionic compounds broken down into their individual ions. Finally, remove the spectator ions by canceling out identical ions on each side of the equation.

Did this summary help you?
  • Include all states of matter for every species in all equations. Youwilllose some marks if you don't.

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Date: 10.12.2018, 01:59 / Views: 92161