Phenylacetic acid 1C6H5CH2COOH2 is one of the substances
that ac...

Question

Phenylacetic acid 1C6H5CH2COOH2 is one of the substances 
that accumulates in the blood of people with phenylketonuria, 
an inherited disorder that can cause mental retardation 
or even death. A 0.085 M solution of C6H5CH2COOH 
has a pH of 2.68. Calculate the Ka value for this acid.

Accepted Answer

Hi everyone this problem reads lactic acid is over produced by the body of a person with lactic acidosis a 0.21 molar solution of lactic acid has a ph of 2.27. What is the K. A. Value for the acid? So our K. A. Value is our acid dissociation constant. And we first need to think about whether or not this is a strong or weak acid. Okay so lactic acid does not fall onto our list of strong acid. So this is a weak acid and a weak acid will say will have lactic acid be represented by H. A. When this dissociates it does not dissociate completely into its ions. It has hydro knee um ions plus its conjugate base. Okay. And so our K. A. Value or acid dissociation constant is going to be equal to the product of the concentrations of our products over the concentrations of our reactant. So we have our concentration of hydro knee um times our concentration of the conjugate base divided by the concentration of our weak acid. And in order for us to solve for the K. A. We're going to need to know the concentration of our hydro knee. Um And because we were given the P. H. And the problem we can solve for the concentration of hydro knee. Um And that's because our concentration of hydrogen ions is equal to 10 to the negative P. H. So we we know what our ph is. So that means we can solve for our concentration of hydro ni um ions. So we take 10 to the negative 2.27. Okay and this gives us 5.3703 times 10 to the negative three. Now our concentration of hydro knee um ions is going to be equal to our concentration of conjugate base. So this number is the same. Okay, so now we need to solve for our concentration of lactic acid, our weak acid which is in the denominator here. So our concentration of our weak acid is going to equal the starting modularity. So we have 0.21 minus our concentration of hydro nia my on. So we have minus 5. times 10 to the neck three. Okay, so we get 0.2046. So now we have all of the values that we need. So let's go ahead and plug into our K. A. Expression here. So because our concentration of hydrogen ions and conjugate base is the same, we're going to say this is going to equal 5.3703 times 10 to the -3 Squared. And our concentration of weak acid we solved is 0.2046. Okay, so doing that calculation, we're going to get a K. A. Is equal to 1.4 times 10 to the negative four. Okay, so this is our final answer. Alright, So our our acid dissociation constant is 1. times 10 to the -4. That's it for this problem. I hope this was helpful.

Phenylacetic acid 1C6H5CH2COOH2 is one of the substances that accumulates in the blood of people with phenylketonuria, an inherited disorder that can cause mental retardation or even death. A 0.085 M solution of C6H5CH2COOH has a pH of 2.68. Calculate the Ka value for this acid.

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