Calculate ph and % hydrolysis in a 1m nacn solution .
Answers
Answer:
Equation 1: HCN+H
2
O
−⇀
↽−
H
3
O
++CN
−
As you correctly note, this is to remind you of the definition for Ka
Equation 2: NaCN⟶Na
++CN
−
Note that I've changed
−⇀
↽−
to ⟶. This is because most sodium salts fully dissociate in aqueous solution and so this "equilibrium" doesn't exist and you can then consider all NaCN to be converted to CN
− for your "initial" stage in the ICE table. Hence there's no need to write an ICE Table with respect to Equation 2.
Value of writing this out: In the case that you were given something sparingly soluble or did not fully dissociate, you would have to consider another equilibrium and this equation 2 would become significant. But in this case, Na
+ is a spectator ion which you can ignore.
Where does Equation 3 come from?
Equation 3 comes from the question itself (or rather what is happening in the system described). Remember, you've got a 1.0M solution of NaCN. Since we've already established that it fully dissociates, at the "initial" stage of the system you have only Na
+ and CN
− ions floating around. But from Equation 1 you know that HCN is a weak acid and so free CN
− in water may act as a base and take a proton from water, and that is given by the equation:
CN
−+H
2
O
−⇀
↽−
HCN+OH
−