O Level Chemistry & IP Chemistry Notes by 10 Year Series Author - Chemistry Specialist

O Level Chemistry Made Easy

O-Level Chemistry: Determination of Ionic Equation & Spectator Ions

During the O Level Chemistry’s Mole Calculation Mastery Workshop over the last weekend, i noticed that many students do not know how to obtain an Ionic Equations when given a question that has information based on word equation. In fact, i always observe this problem whenever a new student joins in my Sec 3 or Sec 4 O-Level Chemistry Tuition Classes.

In order to benefit more students, especially those avid readers and learners (both locally and overseas), let me share with you the simple 7 steps that are required for you to obtain the Ionic Equation.

Step 1: Write down the Chemical Formulae of reactant & products.

Step 2: Check the number of atoms of each element on both sides.

Step 3: Balance the Equation.

Step 4: Add the State Symbol

Step5: Identify Ionic Compounds/Substances that are soluble in water & split into ions

Step 6: Identify Spectator Ion(s) from equation

Step 7: Cancel out the Spectator Ions & write final Ionic Equation

Let’s take an example to dicuss:

Consider this example:
“Sodium Chloride solution are added to Silver Nitrate solution to form 2 products, a soluble Sodium Nitrate Solution and a insoluble Silver Chloride precipitate. Determine the Ionic Equation and the Spectator Ion(s).”

Working:

Balanced Chemical Equation:
NaCl(aq) + AgNO3(aq) –> AgCl(s) + NaNO3(aq)

Splitting of ions:
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq) –> AgCl(s) + Na+(aq) + NO3-(aq)

Cancellation of Spectator Ions (appear on both LHS and RHS):
Na+(aq) + Cl- (aq) + Ag+(aq) + NO3-(aq) –> AgCl (s) + Na+(aq) + NO3-(aq)

Species that are left over will make up the Ionic Equation:
Cl- (aq) + Ag+ (aq) –> AgCl (s) ———————– Final Ionic Equation!

Spectator Ions are: NO3-(aq) & Na+(aq)

PS: Let us know how you find about the strategy shown above. Do drop us a comment directly below this post.

PPS:

Updates in 2011! I have made a video on Writing Ionic Equations!

View the video at: http://www.simplechemconcepts.com/o-level-chemistry-videos-on-writing-ionic-equations/

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Comments

  1. Hi Haris, thanks for the suggestion. We will look into making this Chemistry blog even more intuitive for our readers. Hope you are benefitting from it.

    To Your Chemistry Success,
    Sean Chua

  2. Sean , brilliant attempt but to make your site more efficient you should put a periodic table on side of your equation concepts (e.g. for confirmation of right elements for given equations).
    Regards and thanks by,
    Haris Hassaan.

  4. Hi Abdul,

    For the quick grasp of these COMMON polyatomic ions, we usually ask our students to remember some of the common ones that you will usually encounter in Chemistry examinations.

    For “carbonate” based polyatomic ions, we usually only encounter two types in Cambridge GCE O-Level and A-Level Chemistry, which are:

    Carbonate ion CO32-
    Hydrogencarbonate ion HCO3-

    If you have learned about Oxidation States / Numbers, you will know that Hydrogen will have an oxidation state/number of +1 in compounds.
    So from the above formulae, you can easily remember that the CO32- (carbonate ion) and HCO32- (hydrogencarbonate ion) differs only by a H atom.
    This also means that the charge of the polyatomic ion should be 1 less.

    Hope the above information helps.

    Sean Chua 🙂

  7. Hi Aisha,

    Just realised that this reply came in much later but i guess late is better than never when it comes to learning.

    Spectator Ions are usually the ions that you CANCEL away and does not leave in the Ionic Equation.

    Hope the above helps!

    Cheers!
    Sean Chua

  8. how do we figure out the spectator ions in any ionic equations …i am waiting for the reply this question is very confusing so help me fast as its urgent bcuz tommorrow i have a test

    thanks
    aisha

  9. how to figure out spectator ions in any ionic equation?its urgent ..please explain a bit in detail and clerly

  10. Hi Vanna,

    That is a brilliant question!

    Cos it also confuse students (sometimes school teachers also when their students ask them in class and many got dumbfolded).

    This is known as Halogen Displacement Reaction and is usually covered in the topic of The Periodic Table & Group Trends (if you are studying GCE O-Level Chemistry) OR Chemical Periodicity (if you are in IB or IP school) in Singapore.

    The trick is to know that Cl2 is a diatomic covalent molecule and they wont dissociate (“break”) so easily. So in writing Ionic Equation, we will NOT break them into ions.

    So you will have the following:

    Cl2(aq) + 2K+(aq) + 2I-(aq)
    –> 2K+(aq) + 2Cl-(aq) + I2(aq)

    and if you follow Step 7, you will get the Ionic Equation to be:

    Cl2(aq) + 2I-(aq)
    –> 2Cl-(aq) + I2(aq)

    Hope the above explanation helps!

    Cheers,
    Sean Chua

    PS: Feel free to share it with your friends

  11. Hi AL,

    Hello JJ and ALL,

    Your teacher should have introduced the Table of Solubility of Common Salts to you when they taught you ACIDS, BASES & SALTS.

    You can refer to the link below to find out more:
    http://www.simplechemconcepts.com/?s=table+of+solubility+of+salts

    For more questions, you can check out your textbook or Cambridge Ten Years Series. Alternatively, you can search “Ionic Equations” on the search bar on the top right hand corner of http://www.SimpleChemConcepts.com.

    Cheers!
    Sean Chua

    PS: Feel free to share with your friends

  12. You need to break them up into their respective ions. Important is that the overall charge of both the positive and negative ions must balance!

    So that the compound has net zero charge.

    Cheers!
    Sean Chua

    PS: Feel free to share with your friends

  14. Only those compounds which are in (aq) state symbol will break up into their respective ions.

    E.g.

    HCl(aq) –> H+(aq) + Cl-(aq)

    Na2SO4(aq) –> 2Na+(aq) + SO42-(aq)

    Hope that helps!
    Sean Chua 🙂

  15. Again, i do not try to remember the answer. Some teachers ask their students to memorise ionic equations for key chemical reactions! Which i totally disagree cos it is the wrong way to study and master Chemistry.

    Correct way is to work the solution out step-by-step. For this question, i would like you to know that CaSO4 is a sparingly soluble salt i.e. sometimes it is soluble in water and sometimes it is insoluble in water.

    If the question really ask you for the ionic equation, i reckon that they want you to assume that CaSO4 is soluble in water. i.e. aqueous state.

    H2SO4(aq) + CaCO3(s)
    –> CaSO4(aq)+ H2O(l) + CO2(g)

    If you follow the steps as shown in my example above, you will get:

    2H+(aq) + CaCO3(s)
    –> Ca2+(aq) + H2O(l) + CO2(g)

    as the Ionic Equation.

    Hope you all find the discussion useful!

    Sean Chua 🙂

    PS: Feel free to share with your friends

  16. Hey all:)

    I was wondering for displacement reactions for example:
    Cl2 (aq) + 2KI (aq) -> 2KCl (aq) + I2 (aq)

    How do you know which is the spectator? Because from what I know one way to find out the spectator ions are he ones did not change state through the equation, however for this one all the compounds etc are (aq) throughout! So I was wondering whether anybody could answer my Qs!

    And is there a general rule to help sieve out the spectator ions?
    Ps: I know that spectator ions do not take part in the equation

  18. Can you give me some tips on mastering it? Probably a few questions to practice? It will meant a lot to me! Also how can I tell whether if the chemicals are solid or not? If it is by memory then is there a easier way to remember it? Thanks!

  20. Step 4, add the state symbol…
    How do you know what state each are in???
    Like which one is the solid?

  21. Hi, I am still confused on how to figure out which parts of the original equation will break up and which to keep together. Can you help please

  23. hey,what about those type of equations that have only one aqueous compound? like H2SO4 + CaCO3 = CaSO4 + H2O + CO2, whereby only sulfuric acid is in aqueous state here, calcium carbonate and calcium sulfate both is solid

  24. Spectator Ion is in AQUEOUS STATE. Check out the example above and see how we determine the Spectator Ion(s).

    Hope this helps. Think about it.

  25. Titration only for SPA salts preparation.

    SPA = Sodium, Potassium and Ammonium Salts.

  26. Hi,
    I just wanted to know if an element changes its state symbol during the reaction then is it still a spectator ion? My head says no because that means that it has taken part during the reaction but I am not 100% sure, and I’d just like to check.
    Thanks!

  27. Sir Sean,
    i wanted to ask, how do we know, we have to do titration or add excess while obtaining the salt of BaSO4 .. please urgent help required. thanks

  28. Absolutely YES! Please remember the table to solubility of common salts. Chemistry students should know it well as it is related to many other chemistry topics.

  29. Silver is a Metal and will lose electrons to form Positive Ion. In this case, it will achieve noble gas configurations.

    Hope this helps.

  30. Hi Angi,

    Why not you write me the Balanced Chemical Equations for the reaction below, including their state symbols?

    A) Magnesium Oxide + Hydrochloric Acid

    &

    B) Sodium Hydroxide + Hydrochloric Acid

    PS: You can propose to me their Ionic Equations and Spectator Ions also. I will check for you.

    Look forward to hearing from you.

    Cheers!

  31. Can you write down the Balanced Chemical Equation and their State Symbols HERE?

    I will walk you through step-by-step once i have the above from you.

    Look forward to hearing from you.

    Cheers!

  32. Hi Shenel,

    This is not that difficult. In fact it is very easy if you follow the steps and sequence above.

    All you need is more questions to practice in order to gain the confidence.

    You can master this just like many of our students that comes for our workshops and classes.

    Cheers!

  33. Hi Angi,

    There are no cheat ways. Important thing is to understand and memorise the Table of Solubility of Common Salts.

    After which, you need to follow the steps and sequence as stated above.

    It is actually very easy to do so. You need to practice to gain the confidence of doing it.

    Hope this helps.

  34. Thanks for the support and encouragement.

    Feel free to drop by to discuss questions or comment on our blogposts.

    Cheers!

  35. I GET ITTTTTT!! thanks a lot this makes it easier, except, do we have to learn the solubility rules in order to figure out which ions split in water?

  37. hi im really loving the method you used in your example

    i was wondering whether you could post up some more examples.. so that all of US get the hang of it!

    maybe something with hydrochloric acid (example from my book)

    im currently doing AS chemistry in the uk. Edexcel board.

  38. hi i was wondering whether there was a, “cheat” way of doing the ionic equations..

    what i mean by that is whether there’s a way that will ensure i get every ionic equ. question right..

    for me right now.. its a 50/50 chance game

    hope you can help mr. sean

    cheerz

  40. hey am struggling in my chem class with this ionic equation thing and i need some help as soon as possible.however i think i get this whole spector thing.plz reply.sos

  42. hi am kind of getting the whole spector thing wat am not getting is the forming of the ionic equation.i really need some help as soon as possible am about to do my end of year exam the first 2 weeks of next month.

  43. in fact as far as conditions are favourable for the neutralization reaction only you can say they r not reacting but in away certainly they will make salt

  44. spectator ions are those which remain same on the same side of the equation
    here main reacton is in between H+ and OH- so spectator ions would be Na+ and Cl-!

  46. Hi Sherry,

    The above chemical equation is Neutralisation Reaction.

    As such, the standard Ionic Equation is H+ + OH- –> H20.

    Hope this helps.

    Btw, where are you from? Country and which educational system do you follow?

    Rgds
    Sean
    Master Trainer

  48. how about in the following reaction… can someone pls help me identify the spectator ions in the following neutralisation reaction

    NaOH + HCl —-> NaCl + H2O

    thanks!!

  50. Those which you canceled out are consider as Spectator ions. They have not taken part in any chemical reactions. =)

  51. can i ask, how do you know which of the following was Spectator Ions and which was not? 🙁

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