Methyl violet is an indicator that changes color over a range from pH=0 to pH=1.6. What is the Ka of methyl violet?

u forgot to convert it to Pka .. its Ka value not Pka .. it should be 0.16 which is wrong .. i don't knw y ..

Nick Hoins and Demi Higgins PDA way too much in school!!!

dr bob you are wrong.

You got the correct pka value, but you need to take the anti log of that value to get Ka.

Answer is 0.158

hector.. that is unnecessary and inappropriate. glad to know we make it on a homework help site.

To find the Ka value of methyl violet, we need to use the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

Where pH is the desired pH (in this case, pH=1.6), pKa is the negative logarithm of the acid dissociation constant, [A-] is the concentration of methyl violet in its basic form, and [HA] is the concentration in its acidic form.

Since we know the pH and want to find the pKa, we can rearrange the equation:

pKa = pH - log([A-]/[HA])

Now, let's substitute the given values into the equation:

pH = 1.6

To determine the [A-]/[HA] ratio, we need to consider the range of pH provided (pH=0 to pH=1.6).

When pH=0, the concentration of [HA] is equal to [A-], so the ratio is 1.

When pH=1.6, the concentration of [HA] is 10 times higher than [A-], so the ratio is 1/10.

Now we have all the values to calculate the pKa:

pKa = 1.6 - log(1/10)

Simplifying the equation:

pKa = 1.6 + log(10)

Taking the logarithm of 10 is 1:

pKa = 1.6 + 1

Therefore, the pKa value of methyl violet is 2.6.

We can convert the pKa to the Ka value using the equation:

Ka = 10^(-pKa)

Substituting the pKa value we found:

Ka = 10^(-2.6)

Calculating:

Ka ≈ 2.5 x 10^(-3)

Therefore, the Ka value of methyl violet is approximately 2.5 x 10^(-3).

No, I didn't forget to convert it. Surely you can calculate Ka if you have the pKa. And pKa of 0.8 is correct. You may not have the correct number of significant figures or you may not have rounded properly but I stand by my 0.8 = pKa.

The average of (0 + 1.6/2) = 0.8; therefore,

pKa = 0.8