Setting up ICE chart for pH 9.72 with LiOH and HCN

[Nope]

Homework Statement

if the pH is 9.72 for the following 2 bases. what is the initial conc. of the bases
a)LiOH
b)HCN
the answer for a is 10^-4.28, but i don't know how to set up an ice chart

Homework Equations

The Attempt at a Solution

 

[chemisttree]

For a), you don't need an ICE chart. You need pH=-log[H⁺] and [H⁺][OH^-] = 10^-14

 

[Nope]

For a), you don't need an ICE chart. You need pH=-log[H⁺] and [H⁺][OH^-] = 10^-14

Yes, but I still want to know what the ice chart like,
and for b, can you help me to set the ice chart, because HCN is weird
H₃O⁺ + CN^- <--> H₂O + HCN
is this right ?
thanks!

 

[Borek]

CN^- + H₂O <-> HCN + OH^-

Nothing weird, this is Brønsted-Lowry base.

Note: in the case of bases you have to calculate concentration of OH^-, then to convert it to pH.

ICE tables are built exactly the same way as for acids, just OH^- is the product (concentration of water in the case of cyanide is assumed to be not changing and ignored). You will be not able to solve LiOH with ICE table, as LiOH is considered to be a strong base, 100% dissociated, so final concentration of LiOH will be 0 - and you can't divide by zero.

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[Nope]

but,when i wrote out the the species
HCN(aq)
SA_____A
H30+ , H2O , CN-
_______B___ SB
Isn't the SA react with SB?
H3O+ + CN-?

 

[Borek]

HCN(aq)
SA_____A
H30+ , H2O , CN-
_______B___ SB

I am not familiar with this notation, please elaborate.

H3O+ + CN-?

These would react IF there would be enough H⁺ (H₃O⁺). Concentration of water is much much larger, especially if you start with neutral solution.

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