K of Ionic Compounds in Solution

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Amy Xiao 1I
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Joined: Sat Jul 20, 2019 12:15 am

K of Ionic Compounds in Solution

Postby Amy Xiao 1I » Wed Jan 08, 2020 11:21 pm

"A final point is that, when a reaction involves fully dissociated ionic compounds in solution, the equilibrium constant should be written for the net ionic equation by using the activity for each type of ion. The concentrations of the spectator ions cancel and so do not appear in the equilibrium expression." (pg. 401, 5G.2)

Can someone explain what this means?

Sanjana K - 2F
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Re: K of Ionic Compounds in Solution

Postby Sanjana K - 2F » Thu Jan 09, 2020 12:17 am

Basically, it's telling you to ignore spectator ions like Li+, Na+, K+, Rb+, Sr2+, Ba2+, Cl-, Br-, I-, NO3-, ClO4-, SO4(2-), etc. because these ions occur in the same form on the left and right side of the chemical equation. So when you're writing your equilibrium constant expression they'd cancel anyway.

Brooke Yasuda 2J
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Re: K of Ionic Compounds in Solution

Postby Brooke Yasuda 2J » Thu Jan 09, 2020 10:25 am

When you have a reaction involving ionic compounds in a solution you want to rewrite the equation as the net ionic equation. This means, not writing anything that repeats on both sides of the equation, and would cancel out. This includes spectator ions, which are ions that come from an ionic compound that remain unreacted on both sides of the equation. Leave these out from the K expression.

505316964
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Joined: Thu Jul 11, 2019 12:17 am

Re: K of Ionic Compounds in Solution

Postby 505316964 » Thu Jan 09, 2020 11:19 am

A net ionic equation should only include what participates in forming the product, which is why you leave out spectator ions (ions that merely "spectate" without contributing). Spectator ions appear on opposite sides of a chemical equation and therefore cancel out.

Amy Xiao 1I
Posts: 101
Joined: Sat Jul 20, 2019 12:15 am

Re: K of Ionic Compounds in Solution

Postby Amy Xiao 1I » Fri Jan 10, 2020 12:11 am

Sanjana K - 2F wrote:Basically, it's telling you to ignore spectator ions like Li+, Na+, K+, Rb+, Sr2+, Ba2+, Cl-, Br-, I-, NO3-, ClO4-, SO4(2-), etc. because these ions occur in the same form on the left and right side of the chemical equation. So when you're writing your equilibrium constant expression they'd cancel anyway.


Thank you for providing examples of these spectator ions!


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