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?

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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?

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Weak Acids concept. If you need more Weak Acids practice, you can also practice Weak Acids practice problems.

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Based on our data, we think this problem is relevant for Professor Li & Thompson's class at PURDUE.

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Our data indicates that this problem or a close variation was asked in Chemistry: The Molecular Nature of Matter and Change - Silberberg 8th Edition. You can also practice Chemistry: The Molecular Nature of Matter and Change - Silberberg 8th Edition practice problems.