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Ch.18 - Chemistry of the Environment
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232당신이 사용하는 게 아니라요?교과서 변경
18장, 문제 37

What is the molarity of Na+ in a solution of NaCl whose salinity is 5.6 if the solution has a density of 1.03 g>mL?

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1
Understand that salinity is often expressed in parts per thousand (ppt), so a salinity of 5.6 means 5.6 grams of NaCl per 1000 grams of solution.
Calculate the mass of NaCl in 1 liter of solution using the density: 1.03 g/mL means 1030 g/L. Use the proportion: (5.6 g NaCl / 1000 g solution) = (x g NaCl / 1030 g solution).
Determine the moles of NaCl using its molar mass: NaCl has a molar mass of approximately 58.44 g/mol. Use the formula: moles = mass (g) / molar mass (g/mol).
Since NaCl dissociates into Na+ and Cl- ions in solution, the molarity of Na+ will be equal to the molarity of NaCl because each formula unit of NaCl produces one Na+ ion.
Calculate the molarity of Na+ by dividing the moles of NaCl by the volume of the solution in liters (1 L in this case).

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Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in units of moles per liter (mol/L). To calculate molarity, one must know the amount of solute and the total volume of the solution. In this case, understanding how to convert salinity into moles of NaCl is essential for determining the molarity of Na+.
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Salinity

Salinity refers to the concentration of dissolved salts in water, typically expressed in parts per thousand (ppt) or grams per liter (g/L). In this context, a salinity of 5.6 indicates that there are 5.6 grams of NaCl per liter of solution. This value is crucial for calculating the number of moles of NaCl, which directly relates to the concentration of Na+ ions in the solution.

Density

Density is defined as mass per unit volume and is typically expressed in grams per milliliter (g/mL) or kilograms per liter (kg/L). The density of the solution (1.03 g/mL) is important for converting the mass of the solution into volume, which is necessary for calculating molarity. Understanding how to use density to find the total volume of the solution helps in determining the concentration of Na+ ions.
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Density Concepts
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