Homework Help Forum: To bobpursley

Posted by Chemistry on Tuesday, November 3, 2009 at 5:07pm.

You helped me earlier today whith one of these problems... and i have two more...... What is the ionic and net ionic equation? 1. Ca(HO)2(aq)+ Na2CO3(aq)-> CaCO3 -> (s)+ 2NaOH (aq) I dont understand why there are two arrows? This is what i have so far... Ca+2OH+Na2(aq)+CO3(aq)... 2.KOH+ HBr -> KBr+ H2O Thank you soo much!!! :D

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 5:11pm

  I answered this at an earlier post. The second arrow should ber a + sign. Ca(OH)2 + Na2CO3 ==> CaCO3 + 2NaOH

  
  

• To bobpursley - Chemistry, Tuesday, November 3, 2009 at 5:14pm

  Is the answer you gave the ionic and net ionic equation....

  
  

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 5:18pm

  No. My response only addresses why there is a second arrow. The second arrow shouldn't be there. It should be a + sign. What do you not understand about ionic and net ionic equations. If we can get to your troubler spot you will be able to work these yourself.

  
  

• To bobpursley - Chemistry, Tuesday, November 3, 2009 at 5:21pm

  i do not know how to break down the ions when i know that they are soluble. for example...Ca(HO)2 is soluable but i dont know what to do with the two or what superscripts to use...

  
  

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 5:33pm

  If they are soluble (note the spelling), you break them apart and give each the charge they possess. For example, Ca(OH)2 will break into Ca^+2 and 2OH^-. These are just the valences (or oxidation number) of each. If the material is a precipitate (not soluble) we write it as CaCO3(s) or if it is a weak electrolyte (such as acetic acid, HC2H3O2, or water, H2O, we write them as the molecule. Gases are written as the molecule, also.) Ca(OH)2(aq) + Na2CO3(aq)==>CaCO3(s) + 2NaOH(aq). Then Ca(OH)2 becomes Ca^+2(aq) and 2OH^-(aq), Na2CO3 becomes 2Na^+(aq) and CO3^-2(aq), CaCO3 is written as CaCO3(s) and 2NaOH becomes 2Na^+(aq) + 2OH^-(aq). To change this ionic equation to the net ionic equation you simply cancel ions common to both sides. For example, there are 2OH^- on each side so they cancel. There are two 2Na^+ on each side so they cancel. What is left is the net ionic equation. That is Ca^+2(aq) + CO3^-2(aq) ==> CaCO3(s)

  
  

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 5:36pm

  The ions that cancel are called spectator ions, as Bob Pursley wrote in an earlier post.

  
  

• To bobpursley - Chemistry, Tuesday, November 3, 2009 at 6:02pm

  Thank you so much for giving me a step-by-step! I am homeschooled so i have no one to ask. I have had trouble with this and you are the only thing that has clearly told me how to do this. I only asked bob pursley b/c he gave me the answer last time and i was fustrated and looking for an easy way out. kudos to you!!!! :D

  
  

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 6:04pm

  If you want to do KOH + HBr, we shall be glad to check it for you.

  
  

• To bobpursley - Chemistry, Tuesday, November 3, 2009 at 6:14pm

  okay..... K^+1 + OH^-1 + H^+1 + Br(not sure which ionization number to put here)-> K^+1 + Br + H20 (l) also, i am not sure what the other ions are.... (aq)? is my guess Then the net ionic equation is... OH^-1 + H^+1 -> H2O (l)

  
  

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 6:26pm

  The net ionic equation you wrote is correct. Good work. The complete equation is KOH + HBr ==> KBr + H2O (You would do well to write the complete molecular equation as a first step; otherwise, there is not a smooth flow from molecular to ionic to net ionic equation AND you must try to remember all of those ions since they aren't written anywhere.) You may put the aq if you wish. KOH(aq) + HBr(aq) ==> KBr(aq) + H2O K^+ + OH^- + H^+ + Br^- (you know Br is -1 because H^+ is +1 and all compounds are zero charged (HBr is zero). ==> K^+(aq) + Br^-(aq) Tben the K^+ and Br^- cancel. (Also, Br is in group 17 (or VIIA depending upon the system you are using) and that entire column of F, Cl, Br, I, in column 17 are -1 charged ions in simple compounds such as NaCl, KBr, KI, etc.

  
  

• To bobpursley - Chemistry, Tuesday, November 3, 2009 at 6:37pm

  two more questions.... 1. so when you use the superscript ^- that is the same as saying ^-1 ? 2. what are OH^-1 and H^+1 in the equations? (liquid , or gas)

  
  

• To bobpursley - DrBob222, Tuesday, November 3, 2009 at 7:51pm

  Yes, any time a number is not written, the number 1 is understood; therefore, OH^- means OH^-1 and Na^+ means Na^+1. Likewise, we may write Ca^+2 or Ca^++ which would look like this, Ca+2 or Ca++. If OH^- comes from KOH(aq) then OH^- is OH^-(aq). H^+ comes from HBr; therefore, H^+ is H^+(aq). So the net ionic equation for that KOH + HBr reaction ==> etc would be H^+(aq) + (OH^-)(aq) ==> H2O(l) where (l) is "ell" (for liquid although on my screen it looks like a number 1)

  
  

• To bobpursley - Chemistry, Tuesday, November 3, 2009 at 11:07pm

  Thank you once again for helping me!!!!

  
  

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