Ionic equations - how to know which are the spectator ions

[lboogy]

Hi everyone,

 

I was wondering if you could help me. I am looking at ionic equations, and I'm a little confused. I'm confused about knowing which ions why can omit from the equation. For example:

 

(step 1)HCl(aq)+ NAOH(aq)→NaCl(aq)+H20(l)

 

ions present:

 

(step 2)H+(aq) Cl-(aq) Na+(aq) OH-(aq) → H20(l) Na+(aq) Cl-(aq)

 

So Cl-(aq) & Na+(aq) appear on both sides of the equation and so are spectator ions & can therefore be left out of the equation making the ionic equation:

 

(step 3)H+(aq) OH-(aq) → H20(l)

 

However, what are tghe principles that can be applied to different ionic equations to understand what ions are spectator ions? When deciding what ions are present, how do we know that we should break NaCl down into Cl-(aq) & Na+(aq) but not break H20 down? In step 1, the symbols Na & Cl are together thus NaCl implying to me that they have become 1 molecule & so have reacted. How do we know, by looking at the equation, that they haven't? I hope I've expressed my questions clearly!

 

thanks in advance

Gav

[YT2095]

spectator ions are Product validated.

 

if you wanted to make water then ANY metal OH and ANY H anion would suffice,

 

ie/ KOH and HNO3 making H2O and KNO3 the NO3 and K are the spectators, if you`re only looking at the H2O side.

 

basically they act as a "Vehicle" to carry the Ions that are Interest to you.

[thedarkshade]

Hi!

 

I've also been dealing with these kind of equations recently and sometimes they can be tricky! The equation that you have typed in called "the neutralization equation". That is because the substances formed have pH neutral [pH(NaCl)=7 ; pH(H2O)=7]. And to decide if the reaction is neutralization or the pH scale is acidic or basic, we have to know a few rules for hydrolysis. If strong acids(HCl, H2SO4, HClO4 etc) react with strong basis (NaOH, LiOH etc), then the pH=7, which means neutral. If strong acids react with weak basis (BeOH), then the pH<7, which means acidic medium. If weak acids (CH3COOH, HF, H2CO3 etc) react with strong basis, then pH>7, which means basic medium.

 

I hope any will be useful to you..

 

DraZ

[lboogy]

Hi,

 

thanks for both of the above posts, but my question was more just a general one using a specific example. I am wondering, if I have an equation, how can I tell just by looking at the equation which ions are used in the reaction and which ones aren't? Are there any principles to follow?

[Cap'n Refsmmat]

You need to learn what compounds are soluble and which aren't. Soluble compounds will dissociate into ions, but insoluble compounds aren't. (Anything labeled "aq" or "aqueous" has already dissociated.)

 

Your textbook (if you have one) or Google should have a list of standard solubility rules you can learn to help decide if a compound breaks down.

 

The soluble compounds will split up (like NaCl) into their component ions (e.g. Na+ and Cl-).