Number 71 Chapter 12 Homework

[805132275]

Why does the Na+ get omitted from the CH3Co2??? Is this the case for every compound we are given. I guess I am just confused on how to accurately utilize the Ka values list when the compounds listed are a bit different from those given to us in the questions.

[Nathaniel 2E]

It's because NaCH3CO2 is a salt, and when dissolved in water, the sodium ion dissociates from the CH3CO2-. In full, the reaction is :

Na+ + CH3CO2- + H2O <---> HCH3CO2 + OH- + Na+

But, since the sodium ion is on both sides of the reaction, we can cancel them out and don't need to factor them into the calculation of Ka, because when you calculate the Ka the concentration of Na+ in the products and reactants cancel out. It is simply a way to simplify your calculation. A trick to find out if you can disregard the ion is to look if it is in groups 1 and 2 or is Cl-, Br-, or I-.

[Aili Ye 4L]

Na is simply a spectator ion in the reaction and thus isn't necessarily included.