For which of the following acids would a 1.00 M solution have the lowest pH ( highest H+ concentration)?
b)HC2H3O2, Ka = 1.8 * 10^-5
c)HF, Ka = 7.4*10^-4
d)HCN, Ka = 6.2 *10^-10
Answer:
The pH of 1.00M solution of the acid will depend upon the degree of hydrolysis in water. If the acid is strong one and can dissociate completely than its pH will be low otherwise it may not not go down much as compared with pure water.
Here, the correct answer is HF i.e. option 'C' ,as HF has got the highest Ka value.
Thus, it can be concluded that higher the value of pK lower will be the pH of the solution,.
the acid with the highest Ka will have the lowest pH.
if its easier for you to see, convert the Ka values to pKa values by taking the negative log of the Ka.
pKa = -log Ka
the pKa scale is similar to the pH scale, so the acid with the lowest pKa has the lowest pH.
Ka is a measure of how dissociated the acid is. so figure it out.
HF is the answer.
The right answer is HF.
For a weak acid, [H+] = {cKa}^0.5
So, the acid with highest dissociation constant will have highest H+ ion concentration and lowest pH.
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