A sample of impure tin of mass 0.535 g is dissolved in strong acid to give a solution of Sn2+. The solution is then titrated with a 0.0448 M solution of NO3 -, which is reduced to NO(g). The equivalence point is reached upon the addition of 0.0344 L of the NO3- solution. Find the percent by mass of tin in the original sample, assuming that it contains no other reducing agents.

Stoichiometry is a foundational concept in chemistry that refers to the quantitative relationship between the amounts of reactants and products in a chemical reaction. In titration calculations like the one described in the exercise, stoichiometry allows us to determine the exact amount of one substance (in this case, tin) that reacts with a known amount of another substance (the nitrogen oxide). The balanced chemical equation provides the mole ratio between reactants and products, which is essential for these calculations. The reaction between Sn2+ and NO3- described follows a 1:1 stoichiometric ratio, meaning one mole of Sn2+ reacts with one mole of NO3-. Understanding this ratio enables us to deduce that the moles of Sn2+ in the sample are equal to the moles of NO3- used in the titration.

Redox reactions, or oxidation-reduction reactions, are chemical processes in which electrons are transferred between two substances. The substance that loses electrons is said to be oxidized, and the one gaining electrons is reduced. In the given titration scenario, we are dealing with a redox reaction where tin (Sn2+) is being oxidized to Sn4+, and the nitrate ion (NO3-) is reduced to nitrogen oxide (NO) gas. These kinds of reactions are central to titration calculations because they determine the stoichiometry of the reactants. Recognizing the reactants' oxidation states is critical as it guides us to write the balanced chemical equation correctly and to understand the reaction's stoichiometry, ultimately leading to the correct calculation of the analyte's concentration, and in our case, the percent by mass of tin in the sample.

Percent by mass, also known as mass percent or weight percent, is a way to express the concentration of a component in a mixture or an element in a compound. It is defined as the mass of the component divided by the total mass of the mixture, multiplied by 100%. In the exercise provided, this concept is central to determining the purity of the tin sample. Once we have found the mass of pure tin in the reaction using stoichiometry, calculating the percent by mass involves comparing this mass with the total mass of the impure sample. This value is crucial for quality control in industrial processes and for validating the purity of substances in laboratory settings.

Molar concentration, often expressed in molarity (M), is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per liter of solution. The exercise uses molar concentration to quantify the amount of NO3- present in the solution before titration takes place. By knowing the molarity of the NO3- solution and the volume used at the equivalence point, we can calculate the number of moles of NO3- that have reacted. This calculation is pivotal for stoichiometry because it connects the molar ratio from the balanced equation to the actual amounts of substances involved in the chemical reaction. Consequently, molar concentration is the link between the theoretical mole ratio and the practical aspects of measuring and mixing reactants in a laboratory setting.