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

###### FREE Expert Solution

We are being asked to determine the grams of the hydrochloride that must be dissolved in 10.00 mL of water to give a pH of 3.50

Thiamine hydrochloride (C12H18ON4SCl2) dissociates in water in the following manner

C12H18ON4SCl → C12H18ON4S2+ + 2 Cl-

Cl is neutral so it would not affect pH

C12H18ON4S2+ is a weak acid and it dissociates in water

C12H18ON4S2+ + H2O ⇌ HC12H18ON4S+ + H3O+

We are going to do the following steps

Step 1: Calculate [H3O+]

Step 2: Write Ka expression

Step 3: Determine [C12H18ON4S2+]

Step 4: Calculate mass of thiamine hydrochloride

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###### Problem Details

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