If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Molecular, complete ionic, and net ionic equations

AP.Chem:
TRA‑1 (EU)
,
TRA‑1.B (LO)
,
TRA‑1.B.1 (EK)
,
TRA‑1.B.2 (EK)
,
TRA‑1.B.3 (EK)
In the molecular equation for a reaction, all of the reactants and products are represented as neutral molecules (even soluble ionic compounds and strong acids). In the complete ionic equation, soluble ionic compounds and strong acids are rewritten as dissociated ions. In the net ionic equation, any ions that do not participate in the reaction (called spectator ions) are excluded. As a result, the net ionic equation shows only the species that are actually involved in the chemical reaction. Created by Sal Khan.

Want to join the conversation?

  • piceratops tree style avatar for user Hema Punyamoorty
    In the case of NaCl, it disassociates in Na and Cl. So, can we call this decompostiton reaction?
    (17 votes)
    Default Khan Academy avatar avatar for user
    • piceratops seed style avatar for user RogerP
      No, we can't call it decomposition because that would suggest there has been a chemical change. If you dissolve crystals of NaCl in water, you get a solution of Na+ and Cl- ions, but if you evaporate the water you get back your crystals of NaCl - overall, you've gone through a cycle and nothing has changed.
      (33 votes)
  • duskpin ultimate style avatar for user Dillon Mccarthy
    How do we know which of the two will combine to form the precipitate if we're not given (aq) and (s)?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user astunix
    Why is it that AgCl(s) is not very water soluble even though it is an ionic compound?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • leaf red style avatar for user Richard
      In some ionic compounds the electrostatic forces holding the ions together are stronger than the ion-dipole forces attempting to disrupt the solid lattice. Essentially the amount of energy required to break the silver chloride lattice is larger than solvation by water is able to provide. So silver chloride not dissolving in water, even though one is ionic and the other is polar, is an exception to the "like dissolves like" rule.

      Hope that helps.
      (5 votes)
  • primosaur tree style avatar for user Natalie Price
    How can you tell which are the spectator ions? Isn't NaNo also formed as part of the reaction, meaning that the Cl and Ag ions were the spectators?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • mr pants purple style avatar for user Ryan W
      NaNO3 is very soluble in water so it isn't formed as a compound, Na^+ and NO3^- ions are instead, that is why they both are (aq).

      AgCl on the other hand is not soluble in water, it precipitates out of solution, that is why its state is (s).

      Spectator ions are those that appear on both sides of the equation as ions. They don't take part in the chemical reaction.

      Note that NaNO3 would be formed in addition to AgCl if you removed all the water.
      (4 votes)
  • hopper happy style avatar for user yihualiu83
    At ,would the formula have equal charges or not? Both sides have a charge of 0, but the different charges are different. One side has "+,-,+,-" but the other is just "+,-". Can someone help me, I'm confused.
    (2 votes)
    Default Khan Academy avatar avatar for user
    • piceratops seed style avatar for user RogerP
      As you point out, both sides have a net charge of zero and this is the important bit when balancing ionic equations.

      In ionic equations, precipitates, which are solids, are not written as ions. Hence, AgCl, which is a precipitate, is not written as Ag+ and Cl-.

      In general, solids, gases and liquids (eg, H2O) are not written as ions when writing ionic equations.
      (2 votes)
  • female robot ada style avatar for user Nafia Farzana
    So when compounds are aqueous, unlike in solids their ions get separated and can move around ?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • duskpin ultimate style avatar for user Ardaffa
    What if we react NaNO3(aq) and AgCl(s)? Will it react? Why?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • piceratops tree style avatar for user Hema Punyamoorty
    At , it is said that the compund breaks into individual ions, when dissolved in water. But, if this happens, they will no longer be compunds. How are they be able to retain the characterictics of the initial compund?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • old spice man blue style avatar for user David Du
    Why can't the Na+ and NO3- together form a molecule?
    (1 vote)
    Default Khan Academy avatar avatar for user
    • duskpin ultimate style avatar for user von luger
      They don't bond together here because the compound NaNO3 is soluble in water. In net ionic equations, only the formation of the precipitate is shown, not the soluble compound.
      You can check if a substance is soluble in water by using a solubility chart.
      (3 votes)
  • blobby green style avatar for user tkeerthana
    Whats wrong with this ionic eq?
    Br2(l) + 6OH^- (aq) --> Br^- (aq) + BrO3 ^- (aq) + 3H20 (l)

    is it wrong because the left side has a charge of -1 while the right side has a charge of -2 ? thanks!
    (1 vote)
    Default Khan Academy avatar avatar for user

Video transcript

- [Instructor] What we have here is a molecular equation describing the reaction of some sodium chloride dissolved in water plus some silver nitrate, also dissolved in the water. They're going to react to form sodium nitrate, still dissolved in water, plus solid silver chloride and if you were to look at each of these compounds in their crystalline or solid form before they're dissolved in water, they each look like this. But once you get dissolved in water, and that's what this aqueous form tells us, it tells us that each of these compounds are going to get dissolved in water, they're no longer going to be in that crystalline form, crystalline form. Instead, you're going to have the individual ions disassociating. So for example, in the case of sodium chloride, the sodium is going to disassociate in the water. Sodium is a positive ion, or cation, and so it's going to be attracted to the partially negative oxygen end. Remember, water is a polar molecule. That's what makes it such a good solvent. Now, the chloride anions, similarly, are going to dissolve in water 'cause they're going to be attracted to the partially positive hydrogen ends of the water molecules and the same thing is gonna be true of the silver nitrate. Silver ... The silver ion, once it's disassociated, is going to be positive and the nitrate is a negative. It is an anion. Now, in order to appreciate this and write an equation that better conveys the disassociation of the ions, we could instead write the equation like this. This makes it a little bit clearer that look, the sodium and the chloride aren't going to be necessarily together anymore. The sodium is going to dissolve in the water, like we have here. The chloride is gonna dissolve in the water. The silver ions are going to dissolve in the water and so are the nitrate ions. So this makes it a little bit clearer and similarly on this end with the sodium nitrate stays dissolved so we can write it like this with the individual ions disassociated. But the silver chloride is in solid form. You can think of it as precipitating out of the solution. This is not ... This does not have a high solubility, so it's not going to get dissolved in the water and so we still have it in solid form. Now you might say, well which of these is better? Well it just depends what you are trying to go for. This form up here, which we see more typically, this is just a standard molecular equation. Molecular ... Molecular equation. It's in balanced form. We always wanna have our equations balanced. This right over here is known as a complete ionic equation. The complete's there because we've put in all of the ions and we're going to compare it to a net ionic equation in a second. Complete ionic equation, sometimes just known as an ionic equation. Now why is it called that? Well, 'cause we're showing the individual ions as they're disassociated in water. Now, what would a net ionic equation be? Well let's think about that a little bit. Let me free up some space. So one thing that you notice, on both sides of this complete ionic equation, you have the same ions that are disassociated in water. So for example, on the left-hand side you have the sodium that is dissolved in water and you also have on the right-hand side sodium dissolved in the water. It's not, if you think about the silver chloride being the thing that's being produced, this thing is in ionic form and dissolved form on both sides of this reaction and so you can view it as a spectator, and that's actually what it's called. It's called a spectator ion. Spectator ion. If you wanna think of it in human terms, it's kind of out there and watching the reaction happen. Its value in this reaction is, well it was part of the sodium chloride and its providing ... So the sodium chloride is providing the chloride that eventually forms the silver chloride, but the sodium is just kind of watching. Similarly, you have the nitrate. The nitrate is dissolved on the left and the nitrate is dissolved on the right. So the nitrate is also a spectator ion. So if you wanna go from a complete ionic equation to a net ionic equation, which really deals with the things that aren't spectators, well you just get rid of the spectator ions. You get rid of that. You get rid of that. You get rid of that. You get rid of that, and then you see what is left over. Well what we have leftover is we have some dissolved chloride, and we write aqueous to show that it is dissolved, plus some dissolved silver, plus some dissolved silver. Once again, to show that it's dissolved we write aqueous and if you put those two together, you are going to get some solid silver ... Solid silver chloride. And what's useful about this form, one it's more compact and it's very clear what is actually reacting, what is being used to build, and you can say hey, however you get your chloride into the solution, however you get your silver into the solution, these are the things that are going to react to form the solid. Instead of using sodium chloride, maybe you use potassium chloride and the potassium in that case would be a spectator ion. But either way your net ionic equation would be what we have here.