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When we mix chemical solutions, a solid can form, called a precipitate. This happens when ions in the solutions combine to make an insoluble compound, which separates from the liquid. In this exercise, an excess of sodium hydroxide (NaOH) was added to a solution containing iron(III) nitrate and sodium chloride. The reaction between the iron(III) ions and hydroxide ions produces iron(III) hydroxide, written as \( \mathrm{Fe(OH)}_3 \). This is the precipitate that forms, and it can be filtered out of the solution. The mass of the precipitate is crucial for further calculations, as it provides a way to determine the amount of iron present in the original sample. Understanding the role of precipitates helps in separating and identifying substances in mixtures.

Molar mass is a critical concept in chemistry, used to convert between grams and moles of a substance. It is the mass of one mole of a given substance, composed of the atomic masses of its constituent elements. It's typically expressed in grams per mole (g/mol). Let's look at iron(III) hydroxide, \( \mathrm{Fe(OH)}_3 \). To find its molar mass, you need to add up the masses of its elements. Iron (Fe) has a molar mass of approximately 55.85 g/mol. Oxygen (O) is about 15.999 g/mol, and hydrogen (H) is roughly 1.007 g/mol. Since \( \mathrm{Fe(OH)}_3 \) contains one Fe, three O, and three H atoms, you can calculate the molar mass as:**Molar mass of \( \mathrm{Fe(OH)}_3 \)** \[1 \times 55.85 + 3 \times (15.999 + 1.007) = 106.87 \, \text{g/mol}.\] This molar mass lets you convert the mass of \( \mathrm{Fe(OH)}_3 \) precipitate into moles, which is essential for stoichiometric calculations.

Mass percent measures the concentration of a component in a mixture. It tells you the proportion of a particular substance relative to the total mass of the mixture, usually given as a percentage by mass. Calculating the mass percent involves dividing the mass of the component by the total mass, then multiplying by 100. In this example, we find the mass percent of iron(III) nitrate, \( \mathrm{Fe(NO}_3)_3 \), in a sample. First, you calculate the mass of \( \mathrm{Fe(NO}_3)_3 \) using the mass of the iron measured from the precipitate. Then, the mass percent is:**Mass percent formula** \[\frac{\text{mass of } \mathrm{Fe(NO}_3)_3}{\text{total mass of the sample}} \times 100.\] Knowing the mass percent helps in understanding the composition of mixtures and is a common method for expressing concentration in chemistry.