Twenty dietary iron tablets with a total mass of 21.232 g were ground and mixed thoroughly. Then...

Question:

Twenty dietary iron tablets with a total mass of {eq}\rm 21.232\ g {/eq} were ground and mixed thoroughly. Then {eq}\rm 2.898\ g {/eq} of the powder were dissolved in {eq}\rm HNO_3 {/eq} and heated to convert all iron into {eq}\rm Fe^{3+} {/eq}. Additional of {eq}\rm NH_3 {/eq} precipitated {eq}\rm Fe_2O_3\cdot xH_2O {/eq} which was ignited to give {eq}\rm 0.256\ g {/eq} of {eq}\rm Fe_2O_3 {/eq} (molecular weight {eq}\rm 159.69\ g/mol {/eq}). What is the average mass of {eq}\rm FeSO_4 \cdot 7H_2O {/eq} (molecular weight {eq}\rm 278.01\ g/mol {/eq}) in each tablet?

Dimensional Analysis:

Dimensional analysis is a convenient technique when performing calculations. In this method, a given number is multiplied by a fractional conversion factor. This fraction contains a numerator and denominator wherein the units are placed in a way that the desired unit is obtained by eliminating the unit of the given. The conversion factor can have values established in the problem or based on known facts.

Answer and Explanation: 1

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We first convert the mass of {eq}\rm Fe_2O_3 {/eq}, 0.256 g, to moles using its molar mass, 159.69 g/mol:

{eq}\rm 0.256~g~Fe_2O_3 \times...

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Dimensional Analysis Practice: Calculations & Conversions

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Chapter 17 / Lesson 1
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In physics, dimensional analysis is a tool for deciding mathematical operations and converting units. Review the definition of dimensional analysis and its applications for conversion, speed, math questions, and chemistry.


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