A batch of sodium hydroxide was found to contain sodium chloride as an impurity. To determine the amount of impurity, a \(1.00\)-g sample was analyzed and found to require \(49.90 \mathrm{~mL}\) of \(0.466 \mathrm{M}\) \(\mathrm{HCl}\) for neutralization. What is the percent of \(\mathrm{NaCl}\) in the sample?

Neutralization reactions are a fundamental concept in chemistry. They occur when an acid and a base react to form water and a salt. In the specific case of the exercise, sodium hydroxide (NaOH) acts as the base, and hydrochloric acid (HCl) acts as the acid. The reaction is as follows:

NaOH + HCl → NaCl + H₂O.

This reaction is crucial because it helps to determine the amount of an unknown substance (NaCl impurities, in this case) by using the properties of the reactants.

To find the mass of sodium hydroxide in the sample, you need to understand that each mole of NaOH will react with exactly one mole of HCl. The balanced equation shows a 1:1 mole ratio between NaOH and HCl. This 1:1 stoichiometry simplifies calculations by directly relating the moles of HCl used to neutralize the NaOH to the moles of NaOH present.

Neutralization reactions help identify unknown concentrations, compute purity, and are widely used in titrations, a technique used to find the concentration of a given substance in solution.

Percent composition refers to the percentage by mass of each element in a compound. In this exercise, we are calculating the percent composition of sodium chloride (NaCl) in a mixture with sodium hydroxide (NaOH). This helps to determine the purity of a sample by quantifying the amount of an impurity present.

To calculate the percent composition, first, find the mass of the component of interest (NaCl in this case). After determining the mass of NaCl from the total sample mass and subtracting the mass of NaOH, you can find the percent composition using the formula:

\[ \text{Percent}(\text{NaCl}) = \frac{\text{Mass}(\text{NaCl})}{\text{Total Mass}} \times 100\text{%} \]

Applying this to our problem, after we have calculated the mass of NaCl as 0.070 g in a 1.00 g sample, the percent composition is:

\[ \text{Percent}(\text{NaCl}) = \frac{0.070 \text{ g}}{1.00 \text{ g}} \times 100\text{%} = 7.0\text{%} \]

Using percent composition is essential in chemistry for assessing the purity of substances, quality control in manufacturing, and in various scientific calculations involving compound formulations.

Molarity (M) is a measure of the concentration of a solution. It is defined as the number of moles of solute (the substance being dissolved) per liter of solution. Molarity is a crucial concept because it allows chemists to prepare solutions with precise concentrations and is used extensively in stoichiometric calculations.

The formula for molarity is:

\[ M = \frac{\text{moles of solute}}{\text{liters of solution}} \]

In the exercise, 0.466 M HCl solution was used, meaning there are 0.466 moles of HCl in every liter of solution. To find the moles of HCl, we use the volume of the HCl solution used (49.90 mL or 0.04990 L) in the following way:

\[ n(\text{HCl}) = M \times V = 0.466 \text{ M} \times 0.04990 \text{ L} = 0.02325 \text{ moles} \]

By knowing the molarity, we can accurately determine the number of moles of HCl, which, due to the 1:1 reaction ratio, directly gives us the moles of NaOH. This relationship highlights how molarity is essential in titration calculations and many other analytical methods in chemistry.