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

In summary, the unit used to measure α, which represents the degree of dissociation of a solute into ions or radicals per mole, is Litre/mol. This is calculated using the formula α = √(Kd/C), where C is the concentration measured in Mol/litre and Kd is the dissociation constant with units of mol/Litre. The formula for Kd is Kd = [A+][B-]/[AB], indicating that Kd is not unit-less but rather has units of mol/Litre.
  • #1
Nader AbdlGhani
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You have to show your attempts, this is a forum policy. Also, all homework like questions should go to homework forum.
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 .
 
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  • #2
Nader AbdlGhani said:
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>
 
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  • #3
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?
 
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  • #4
Borek said:
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
 
  • #5
Nader AbdlGhani said:
Kd doesn't have a unit

Sure it does. Please write the formula.

Besides, I just realized your formula for α looks odd.
 
  • #6
Borek said:
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 .
 
  • #7
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.
 
  • #8
Borek said:
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 .
 
  • #9
I see, that's an approximation only.

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

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

1. What is the unit of measurement for degree of dissociation?

The unit of measurement for degree of dissociation (α) is a dimensionless quantity, as it is a ratio of the number of dissociated molecules to the initial number of molecules in a substance.

2. How is the degree of dissociation represented in equations?

In equations, the degree of dissociation is typically represented by the Greek letter alpha (α) or the symbol ξ (xi).

3. Can the degree of dissociation be greater than 1?

No, the degree of dissociation cannot be greater than 1. It is a measure of the extent to which a substance has dissociated, and a value of 1 would mean that all the molecules in the substance have dissociated.

4. How does temperature affect the degree of dissociation?

Temperature can affect the degree of dissociation as it can alter the equilibrium between the dissociated and undissociated molecules. Generally, an increase in temperature leads to an increase in degree of dissociation for endothermic reactions, and a decrease in degree of dissociation for exothermic reactions.

5. What is the significance of the degree of dissociation in chemical reactions?

The degree of dissociation is important in understanding the behavior of chemical reactions. It can indicate the strength of bonds in a substance, as well as the equilibrium between reactants and products. It is also used in calculating equilibrium constants and in predicting the direction of a reaction.

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