Help with M9

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304922790
Posts: 25
Joined: Fri Sep 29, 2017 7:04 am

Help with M9

Postby 304922790 » Tue Oct 03, 2017 11:28 am

Why is the Na canceled out in the equation (according to the solutions manual)? There is a similar questions posted previously but the answer was not very detailed and I am still confused.

Thanks for your help in advance! :)

Hannah Chew 2A
Posts: 76
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 2 times

Re: Help with M9

Postby Hannah Chew 2A » Tue Oct 03, 2017 1:36 pm

I actually missed this too, but I realize now that the question asks for the net ionic equation. This means that spectator ions like sodium wouldn't be part of the equation unless it was asking for the complete ionic equation.

304922790
Posts: 25
Joined: Fri Sep 29, 2017 7:04 am

Re: Help with M9

Postby 304922790 » Tue Oct 03, 2017 8:52 pm

Hmmm... I only took high school chemistry so I don't really know/ remember what spectator ions are. Can you please expand that for me please? :)

Kourtney Nham 1L
Posts: 20
Joined: Fri Sep 29, 2017 7:04 am

Re: Help with M9

Postby Kourtney Nham 1L » Tue Oct 03, 2017 9:24 pm

Hi! Spectator ions are ions whose forms aren't changed during the reaction. In the question, the original equation would be Cu(NO3)2 + 2NaOH --> Cu(OH)2 + 2NaNO3. Based on solubility rules, the equation in an ionic form would look like Cu2+ + 2NO3- + 2Na+ + 2OH- --> Cu(OH)2 + 2Na+ + 2NO3-. As you can see, both the sodium ions and nitrate ions are unchanged on both sides of the reaction while the copper and hydroxide ions form the precipitate. Net ionic equations are meant to show which ions are actually reacting in the reaction, so you can "cross out" the sodium ions and nitrate ions which leaves you with the answer.

Nina Gautam 1K
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am

Re: Help with M9

Postby Nina Gautam 1K » Wed Oct 04, 2017 11:44 pm

In ionic equations, how do you know when to split up molecules (as Kourtney did for both reactant molecules) vs keeping molecules together? (Such as keeping Cu(OH)2 together in the products but splitting up 2NaNO3 to 2Na+ + 2NO3-?

Charles Ang 1E
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

Re: Help with M9

Postby Charles Ang 1E » Thu Oct 05, 2017 10:58 am

Nina Gautam 1L wrote:In ionic equations, how do you know when to split up molecules (as Kourtney did for both reactant molecules) vs keeping molecules together? (Such as keeping Cu(OH)2 together in the products but splitting up 2NaNO3 to 2Na+ + 2NO3-?


When in an aqueous solution, solubility rules apply. 2NaNO3 is soluble (most molecules with NO3 are), therefore it is split up when writing the ionic equation.


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