   Chapter 4, Problem 128IL

Chapter
Section
Textbook Problem

Thioridazine, C21H26N2S2, is a pharmaceutical agent used to regulate dopamine (Dopamine, a neurotransmitter, affects brain processes that control movement emotional response, and ability to experience pleasure and pain.) A chemist can analyze a sample of the pharmaceutical for the thioridazine content by decomposing it to convert the sulfur in the compound to sulfate ion. This is then “trapped” as water-insoluble barium sulfate (see Figure 4.4).SO42−(aq, from thioridazine) + BaCl2(aq) → BaSO4(s) + 2 Cl−(aq)Suppose a 12-tablet sample of the drug yielded 0.301 g of BaSO4. What is the thioridazine content, in milligrams, of each tablet?

Interpretation Introduction

Interpretation:

The mass of thioridazine C21H26N2S2 content in milligram on each tablet has to be determined.

Concept introduction:

• The relation between the number of moles and mass of the substance is ,

Numberofmole=MassingramMolarmass

Massingramofthesubstance=Numberofmole×Molarmass

• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mol (g/mol).
• For chemical reaction balanced chemical reaction equation written in accordance with the Law of conservation of mass.
• Law of conservation of mass states that for a reaction total mass of the reactant and product must be equal.
• Stoichiometric factor is a relationship between reactant and product which is obtained from the balanced chemical equation for a particular reaction.
• Amountof substance=Concentrationofsubstance×volumeofthesubstance
• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
Explanation

Balanced chemical equation for the given reaction is,

SO42(aq,fromthioridazine)+BaCl2(aq)BaSO4(s)+2Cl(aq)

From the balanced chemical equation it is clear that SO42 from thioridazine and BaSO4 react in a 1:1ratio.

The amount (moles) of BaSO4 available can be determined as follows,

Amount of BaSO4=   0.301gBaSO4233.38g/mol

=    0.00129mol

Using the stoichiometric factor the amount of thioridazine C21H26N2S2 can be calculated.

Therefore,

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