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# Finding the pH of a solution watch

1. Ok, so im stuck on this particular question which is:

A solution of phenol in water has a concentration of 38 g dm-3.
The acid dissociation constant, Ka of phenol is 1.3 x 10-10 mol dm-3.
Calculate the pH of this solution.

I hate it the most when the unit of something has gdm-3 or other units thats similar because it really puts me off and I never know what to do.

So far I have worked out the moles of phenol (n=m/Mr)
n(Phenol)= 0.404mols
And I would need to find the concentration, but I don't know the volume. Or is that 1000cm3?

2. (Original post by Shammy92)
Ok, so im stuck on this particular question which is:

A solution of phenol in water has a concentration of 38 g dm-3.
The acid dissociation constant, Ka of phenol is 1.3 x 10-10 mol dm-3.
Calculate the pH of this solution.

I hate it the most when the unit of something has gdm-3 or other units thats similar because it really puts me off and I never know what to do.

So far I have worked out the moles of phenol (n=m/Mr)
n(Phenol)= 0.404mols
And I would need to find the concentration, but I don't know the volume. Or is that 1000cm3?

You are told the concentration in grams per litre.

You have converted the grams to moles

So now you have moles per litre.

Now you apply the weak acid equilibrium equation to find [H+] and hence pH

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