(a) A solution of sodium thiosulfate, Na2 S2 O3, is 0.1442 M. 37.00 mL of this solution reacts

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(a) A solution of sodium thiosulfate, Na2 S2 O3, is 0.1442...

(a) $\mathrm{A}$ solution of sodium thiosulfate, $\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$, is $0.1442 \mathrm{M}$. $37.00 \mathrm{~mL}$ of this solution reacts with $28.85 \mathrm{~mL}$ of $\mathrm{I}_{2}$ solution. Calculate the molarity of the $\mathrm{I}_{2}$ solution. $$ 2 \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}+\mathrm{I}_{2} \longrightarrow \mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}+2 \mathrm{NaI} $$ (b) $35.32 \mathrm{~mL}$ of the $\mathrm{I}_{2}$ solution is required to titrate a sample containing $\mathrm{As}_{2} \mathrm{O}_{3} .$ Calculate the mass of $\mathrm{As}_{2} \mathrm{O}$, $(197.8 \mathrm{~g} / \mathrm{mol})$ in the sample. $$ \mathrm{As}_{2} \mathrm{O}_{3}+5 \mathrm{H}_{2} \mathrm{O}(\ell)+2 \mathrm{I}_{2} \longrightarrow 2 \mathrm{H}_{3} \mathrm{~A}_{5} \mathrm{O}_{4}+4 \mathrm{HI} $$

(a) $\mathrm{A}$ solution of sodium thiosulfate, $\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$, is $0.1442 \mathrm{M}$. $37.00 \mathrm{~mL}$ of this solution reacts with $28.85 \mathrm{~mL}$ of $\mathrm{I}_{2}$ solution. Calculate the molarity of the $\mathrm{I}_{2}$ solution.
$$
2 \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}+\mathrm{I}_{2} \longrightarrow \mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}+2 \mathrm{NaI}
$$
(b) $35.32 \mathrm{~mL}$ of the $\mathrm{I}_{2}$ solution is required to titrate a sample containing $\mathrm{As}_{2} \mathrm{O}_{3} .$ Calculate the mass of $\mathrm{As}_{2} \mathrm{O}$, $(197.8 \mathrm{~g} / \mathrm{mol})$ in the sample.
$$
\mathrm{As}_{2} \mathrm{O}_{3}+5 \mathrm{H}_{2} \mathrm{O}(\ell)+2 \mathrm{I}_{2} \longrightarrow 2 \mathrm{H}_{3} \mathrm{~A}_{5} \mathrm{O}_{4}+4 \mathrm{HI}
$$

Key Concepts

Titration

Titration is an analytical technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration. The point at which the reaction is complete, often indicated by a color change or another signal, allows the use of stoichiometric relationships to calculate the desired concentration or amount.

Mole Concept and Mass-Mole Conversions

The mole concept links the number of particles in a substance to its mass by using a substance's molar mass, which is essential for converting between the mass of a substance and the number of moles. This conversion is critical in quantitative chemical analyses and mass calculations based on stoichiometry.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced chemical equation. This concept uses mole ratios derived from the equation to convert between the amounts of different substances involved in the reaction, making it crucial for determining unknown concentrations or masses.

Molarity

Molarity is the concentration of a solution expressed as the number of moles of solute per liter of solution. It is a fundamental concept in solution chemistry that is used to relate the amount of substance present to the volume of the solution and is essential for quantitatively analyzing reactions in solution.

Balanced Chemical Equations

A balanced chemical equation represents the conservation of mass and atoms in a chemical reaction by showing the exact mole ratios of reactants and products. This is essential in titration and other quantitative analyses because it provides the basis for stoichiometric calculations.

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