The unit of measurement of degree of dissociation ( α ) ?

[Nader AbdlGhani]

What's the unit used to measure α ? if α=(Kd/C)^0.5 where Kd is the dissociation constant and C is the total concentration of electrolyte .

 

[drvrm]

What's the unit used to measure α ? if α=(Kd/C)0.5 where Kd is the dissociation constant and C is the total concentration of electrolyte .

perhaps ..degree of dissociation refers to the
amount of solute dissociated into ions or radicals per mole. its denoted by alpha.

The classical Theory of electrolytic dissociation,is based on the assumption of the incomplete dissociation of the solute,
characterized by the degree of dissociation α, that is,the fraction of the electrolyte molecules that dissociate.
for details ; see <http://encyclopedia2.thefreedictionary.com/Electrolytic+Dissociation>

 

[Borek]

Why don't you plug units into the formula and see what you get? What is the unit of the concentration? What is the unit of Kd?

 

[Nader AbdlGhani]

Why don't you plug units into the formula and see what you get? What is the unit of the concentration? What is the unit of Kd?

I've already done that , but before I did so , my teacher had told me it's unit-less , he said that according to our school textbook , according to this idea , concentration is measured in mol/Litre and Kd doesn't have a unit as it's a ratio between two constants , therefore the unit of measuring alpha should be Litre/mol ,which sounds a little bit weird

 

[Borek]

Kd doesn't have a unit

Sure it does. Please write the formula.

Besides, I just realized your formula for α looks odd.

 

[Nader AbdlGhani]

Sure it does. Please write the formula.

Besides, I just realized your formula for α looks odd.

I'm sorry but what formula you want me to write ? and what do you mean the formula for alpha looks odd ? thanks .

 

[Borek]

Write the formula for Kd, to see what are Kd units.

α is just the dissociation percentage (fraction), I don't see how it can be calculated using formula you gave in the opening post.

 

[Nader AbdlGhani]

Write the formula for Kd, to see what are Kd units.

α is just the dissociation percentage (fraction), I don't see how it can be calculated using formula you gave in the opening post.

If $\mathbf{AB \leftrightarrow A^+ + B^-}$ then $\mathbf{K_d=\frac{[A^+][B^-]}{[AB]}}$
then $\mathbf{K_d=\frac{α^2C}{1-α}}$ , and $\mathbf{1-α\approx1}$ therefore $\mathbf{α=\sqrt{\frac{K_d}{C}}}$ where C (concentration) is measured in Mol/litre and $K_d$ is unit-less .

 

[Borek]

I see, that's an approximation only.

Why do you think K_d is unit-less? You wrote a formula - what does it tell you?