- Oxidation–reduction (redox) reactions
- Worked example: Using oxidation numbers to identify oxidation and reduction
- Balancing redox equations
- Dissolution and precipitation
- Precipitation reactions
- Double replacement reactions
- Single replacement reactions
- Molecular, complete ionic, and net ionic equations
- Molecular, complete ionic, and net ionic equations
- 2015 AP Chemistry free response 3a
Molecular, complete ionic, and net ionic equations
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.
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- In the case of NaCl, it disassociates in Na and Cl. So, can we call this decompostiton reaction?(17 votes)
- 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.(35 votes)
- How do we know which of the two will combine to form the precipitate if we're not given (aq) and (s)?(8 votes)
- At1:48,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.(6 votes)
- 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.(13 votes)
- At0:50, 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?(7 votes)
- When they dissolve, they become a solution of the compound. It is still the same compound, but it is now dissolved.(7 votes)
- So when compounds are aqueous, unlike in solids their ions get separated and can move around ?(5 votes)
- Yes, that's right. The ions is solutions are stabilised by the water molecules that surround them but are free to move around.(6 votes)
- 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?(3 votes)
- 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.(9 votes)
- Why is it that AgCl(s) is not very water soluble even though it is an ionic compound?(3 votes)
- 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)
- What if we react NaNO3(aq) and AgCl(s)? Will it react? Why?(3 votes)
- It won't react because the NaCl(aq)+AgNO3(aq) has already reacted to create NaNO3(aq)+AgCl(s). Sodium nitrate and silver chloride are more stable together. The reason they reacted in the first place, was to become more stable.(4 votes)
- In the case of NO3 or OH it is hard to tell which molecules will gain/lose electrons (for example, BrOH has an equal amount of valence electrons). Are there any videos or lessons that help recognize when ions are positive or negative?(4 votes)
- How would you recommend memorizing which ions are soluble?(4 votes)
- You don't need to, for any practical reason since tables are provided on some Periodic Table of Elements anyway. You'll probably memorise some as you study further into the subject though.(2 votes)
- [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.