[michael11]

This is a question from my discussion packet that I've been struggling with.

0.5 M solution of NaD (D- is a salt of the weak acid HD with the Ka=2.5x10^-10).
 a. Based on the information given do you have a reaction of acid with water or base with water? Why?

Write down the chemical reaction:

What is the equilibrium expression?(Is that a Ka, Kb, or neither?)

Calculate the value of K for the reaction of D- and water: (hint: use the connection between Ka,Kb, and Kw)

ICE Table:

pOH(at equilibrium)=

pH(at equilibrium)=

[dshipp17]

a. Well, remembering back, a low pKa means either you have an acid or base and a high pKa means either you have a base or acid, I forget which was which, but, it's a quick review; you would have to calculate the pKa from the Ka; it's a logarithmic relationship.
b. Once you determine whether it's acidic or basic, the chemical reaction, expressed as a chemical equation will be straight forward (e.g. either you'll get an acidic or hydronium compound; H+ or OH-, plus water)
And, just checked, if the -log of Ka is low (or pKa=-logKa), it's acidic; if the -log is high, it's basic. Basically, like a pH.

[AWK]

http://www.chemicalforums.com/index.php?topic=65859.0

whenever asking questions show you have already tried to solve them on your own,

[AWK]

a. Well, remembering back, a low pKa means either you have an acid or base and a high pKa means either you have a base or acid, I forget which was which, but, it's a quick review; you would have to calculate the pKa from the Ka; it's a logarithmic relationship.
b. Once you determine whether it's acidic or basic, the chemical reaction, expressed as a chemical equation will be straight forward (e.g. either you'll get an acidic or hydronium compound; H+ or OH-, plus water)
And, just checked, if the -log of Ka is low (or pKa=-logKa), it's acidic; if the -log is high, it's basic. Basically, like a pH.

This is not help, this is a misinformation.
The problem concerns salt formed from weak acid and strong base dissolved in water. The anion of this salt is treated as weak base in Brønsted theory of acids and bases.

[KungKemi]

a. Well, remembering back, a low pKa means either you have an acid or base and a high pKa means either you have a base or acid, I forget which was which, but, it's a quick review; you would have to calculate the pKa from the Ka; it's a logarithmic relationship.
b. Once you determine whether it's acidic or basic, the chemical reaction, expressed as a chemical equation will be straight forward (e.g. either you'll get an acidic or hydronium compound; H+ or OH-, plus water)
And, just checked, if the -log of Ka is low (or pKa=-logKa), it's acidic; if the -log is high, it's basic. Basically, like a pH.

This is not help, this is a misinformation.
The problem concerns salt formed from weak acid and strong base dissolved in water. The anion of this salt is treated as weak base in Brønsted theory of acids and bases.

However, wouldn't the anion act as a stronger base than that of the hydroxide in H₂O? (Kb = 4.0 × 10^-5 for D^-, but Kb = 1 × 10^-7 for hydroxide in water)? As such, would the reversible reaction be expressed as:

D^- + H₂O HD + OH^-

If this is true, would the resultant pH of the solution be slightly basic?

I'm not too sure, I haven't covered these concepts yet in class.

Thanks,
KungKemi

[dshipp17]

a. Well, remembering back, a low pKa means either you have an acid or base and a high pKa means either you have a base or acid, I forget which was which, but, it's a quick review; you would have to calculate the pKa from the Ka; it's a logarithmic relationship.
b. Once you determine whether it's acidic or basic, the chemical reaction, expressed as a chemical equation will be straight forward (e.g. either you'll get an acidic or hydronium compound; H+ or OH-, plus water)
And, just checked, if the -log of Ka is low (or pKa=-logKa), it's acidic; if the -log is high, it's basic. Basically, like a pH.

This is not help, this is a misinformation.
The problem concerns salt formed from weak acid and strong base dissolved in water. The anion of this salt is treated as weak base in Brønsted theory of acids and bases.

However, wouldn't the anion act as a stronger base than that of the hydroxide in H₂O? (Kb = 4.0 × 10^-5 for D^-, but Kb = 1 × 10^-7 for hydroxide in water)? As such, would the reversible reaction be expressed as:

D^- + H₂O HD + OH^-

If this is true, would the resultant pH of the solution be slightly basic?

I'm not too sure, I haven't covered these concepts yet in class.

Thanks,
KungKemi

I checked it and it has a high pH/pKa; so, this is a base (-log of the Ka).

[AWK]

Now the hardest problem

What is the equilibrium expression?(Is that a Ka, Kb, or neither?)

Calculate the value of K for the reaction of D- and water: (hint: use the connection between Ka,Kb, and Kw)

In expression for K one may use Ka and Kb or Kb only.