Calculate the pH of 0.20 M NaCN solution.
NaCN ---> Na+ + CN-
CN- + H20+ ---> HCN+ + OH-
Initial conc. of CN- = 0.20 mol/L
change = -x
equillibrium = 0.20-x
HCN equill. = +x
OH equill. = 1x10^-7+x
Ka= 6.2 x 10^-10
Kb = KW/Ka = 1x10^-14/6n2 x 10^-10 = 1.6 x 10^-5
1.6 x 10^-5 = [x][1x10^-7+x]/0.2
QUADRATIC FORMULA:
x= 1.8 x 10^-3
pOH = -log(1.8x10^-3)
= 2.73
Ph = 14 - POH
=11.26
DID I DO THIS CORRECTLY?
How would I determine whether or not the CN- was an acid or a base. I was thinking this. The HCN is an acid so when you take the H off of it it becomes the conjugate base. Is this also correct?
Calculate the pH of 0.20 M NaCN solution.
NaCN ---> Na+ + CN-
CN- + H20+ ---> HCN+ + OH-
Initial conc. of CN- = 0.20 mol/L
change = -x
equillibrium = 0.20-x
HCN equill. = +x OK to here.
OH equill. = 1x10^-7+x This is also +x.
I will let you redo the math to get pH but I solve for pH and obtained 11.25.
Ka= 6.2 x 10^-10
Kb = KW/Ka = 1x10^-14/6n2 x 10^-10 = 1.6 x 10^-5
1.6 x 10^-5 = [x][1x10^-7+x]/0.2
QUADRATIC FORMULA:
x= 1.8 x 10^-3
pOH = -log(1.8x10^-3)
= 2.73
Ph = 14 - POH
=11.26
DID I DO THIS CORRECTLY?
How would I determine whether or not the CN- was an acid or a base. I was thinking this. The HCN is an acid so when you take the H off of it it becomes the conjugate base. Is this also correct? Yes, HCN is an acid, you remove the H and the CN^- becomes the conjugate base (because it will accept a proton).
I redid it and I got 11.25 :) Thanks :)
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Well, it seems like you've done the calculations correctly!
To determine whether CN- is an acid or a base, you can consider its reaction with water. In this case, CN- reacts with water to form HCN and OH-. Since HCN is a weak acid, CN- can be considered its conjugate base.
So, you're right! When you remove the H+ from HCN, you're left with the CN- ion, which can be considered the conjugate base of HCN.
Keep up the good work! If you have any more chemistry questions, feel free to ask!
Yes, you have done the calculations correctly. The pH of the 0.20 M NaCN solution is approximately 11.26.
To determine whether CN- acts as an acid or a base, you can consider its behavior in water. CN- is the conjugate base of the weak acid HCN. In water, CN- can react with water to form HCN and OH-. This reaction suggests that CN- can accept a proton (H+) from water, making it a base.
Your understanding is correct - when you remove a hydrogen ion (H+) from an acid like HCN, it becomes its conjugate base, in this case, CN-. In other words, the HCN acid donates a proton (H+) to water to form the CN- base and hydronium ion (H3O+).