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Ch.18 - Chemistry of the Environment

Chapter 18, Problem 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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Hey everyone, we're told that a sodium chloride solution has a salinity of 16 point oh and the density of 1.114 g per mil leader were asked to calculate the molar concentration of chlorine ions in the solution. To answer this question, we need to recognize that 1.114 g over mill leader is essentially the same as 1.114 kg over leader. And this will make it easier for us to use in our dimensional analysis. And we also need to recognize that a salinity of 16.0, means that we have 16.0 g of sodium chloride per kilogram of solution. And we can go ahead and assume that we have one kg of solution. Now let's go ahead and answer this question. Starting off with our 16.0 g of sodium chloride per kilogram of solution. Using our dimensional analysis, we're going to take the molar mass of sodium chloride and we know that we have 58. g of sodium chloride per one mole of sodium chloride. Using our multiple ratios, we know that one mole of sodium chloride Is equivalent to one mole of Chlorine Ion. And using our density, we have 1.114 kg per leader. And when we calculate this out and cancel out all of our units, We end up with a molar concentration of 0.305 molar of our chlorine ion and this is going to be our final answer. Now, I hope that made sense. And let us know if you have any questions.