Subject: Chemistry Topic: chemical equilibrium and equilibrium constant In a lab
ID: 480979 • Letter: S
Question
Subject: Chemistry
Topic: chemical equilibrium and equilibrium constant
In a lab experiment, I put potassium chromate in a test tube and then I added drops of sulfuric acid until is changed. After several drops it turned orange. I'm told to write the Keq but I'm given the net ionic equation.
Am I to use the ions, such as Cr2O7^2- or the actual molecules in the standard balanced equation to write the Keq? What could be the purpose of the net ionic equation when every youtube video seems to just use the standard chemical equation. I've emailed my professor several time but I still haven't received a response from her.
Any guess would be very helpful.
Now, I'm also asked whether the equalibrium shifted left or right after adding the sulfuric acid. I want to say that it shifted right since it turned orange. But couldn't a basic standard chemical formula tell me this too?
Explanation / Answer
Am I to use the ions, such as Cr2O7^2- or the actual molecules in the standard balanced equation to write the Keq?
Absolutely, actually, we care more about the ions in solution than those in "solid" state, since those have activity = 1
For individual ions, we could increase/decrase them by adding other types of salt, so we DO care about them
The net ionic equation help us identify which ions are those acutally to be considered in the equation
All other spectator ions, are of no importance in Keq contstant
For Q2:
if you add h2so4, i.e. acid, H+ in solution, this will favour the "orange" specie
Therefore, always consider H+ and all other ions in solutoin if they affect the reactants/products concentrations