Thiamine hydrochloride (C12H18ON4SCl2) is a water-soluble form of thiamine (vitamin B1; Ka = 3.37×10−7). How many grams of the hydrochloride must be dissolved in 10.00 mL of water to give a pH of 3.50?

Explanation:

Hello,

In this case, considering the dissociation of thiamine hydrochloride:

It is convenient to write it as:

Or:

With which the Henderson-Hasselbalch equation is applied:

Therefore:

Thus, as the pH equals the concentration of hydrogen which also equals the concentration of the conjugate base, one obtains:

Now, solving for the concentration of acid ([HA]):

Finally, the mass turns out:

Best regards.