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Chapter 12: Problem 111

A student plans to divide the molarity of his solution by its volume to determine the number of moles of solvent in it. He is making two mistakes here. Identify the mistakes and correct both of them.

Short Answer

Expert verified
The student's mistakes are: (1) confusing solute with solvent, as they are using molarity which measures the concentration of the solute, and (2) dividing molarity by volume, which would give the reciprocal of the volume, not the moles of solvent. To correct these, we should (1) use molality instead of molarity, which relates to solvent mass, and (2) use the relationship: molality = moles of solute / mass of solvent (in kg), to find the moles of solvent using its molar mass.

Step by step solution

01

Mistake 1: Confusing solute with solvent

The student wants to find the number of moles of solvent, but instead, they are using the molarity of the solution, which is actually a measure of the concentration of the solute in the solution. The relationship between molarity and moles of solute is given by M = moles of solute / volume of solution (in liters). It is important to distinguish between solute and solvent.
02

Correction 1: Use molality instead of molarity

To find the number of moles of solvent, we need to use the concept of molality (m), which is the ratio of moles of solute to the mass of the solvent (in kilograms). Given the molality of the solution, we can find the mass of the solvent and then use that information to find the number of moles of solvent.
03

Mistake 2: Dividing molarity by volume

The student plans to divide the molarity of the solution by its volume to find the number of moles of solvent. However, this calculation would actually give a value that represents the reciprocal of the volume, not the number of moles of solvent.
04

Correction 2: Use the proper relationship to find moles

To find the number of moles of solvent, we should use the relationship between molality, moles of solute, and mass of solvent: molality (m) = moles of solute / mass of solvent (in kg) If we know the molality of the solution and the moles of solute present, we can solve for the mass of the solvent (in kilograms) and then find the number of moles of solvent using its molar mass. This will give us the correct value for the moles of solvent in the solution.

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Most popular questions from this chapter

Your assistant tells you she measured out \(2.50\) moles of \(\mathrm{NaCl}\) and then added enough water to get \(500.0 \mathrm{~mL}\) of solution to prepare a \(5.00 \mathrm{M}\) solution of \(\mathrm{NaCl}\). (a) What was the mass of the \(\mathrm{NaCl}\) in grams? (b) Did she successfully prepare a \(2.5 \mathrm{M}\) solution? Prove your answer.

A \(25.00 \mathrm{~mL}\) sample of aqueous sulfuric acid of unknown concentration is neutralized by \(27.55\) \(\mathrm{mL}\) of \(1.0002 \mathrm{M} \mathrm{NaOH}(a q)\) (a) Write a net ionic equation for this acid-base neutralization reaction. (b) How many moles of \(\mathrm{NaOH}\) did it take for the neutralization? (c) How many moles of sulfuric acid were neutralized? (d) What is the molar concentration of the sulfuric acid?

A student combines \(60.0 \mathrm{~mL}\) of \(0.250 \mathrm{M} \mathrm{NaOH}\) with \(60.0 \mathrm{~mL}\) of \(0.125 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\). What is the hydroxide ion molar concentration in the resulting solution?

Which one of the following steps in the dissolving process must have a negative value for \(\Delta E\) ? Explain your answer. (a) The physical separation of solute particles (b) The formation of solvent-solute interactions (c) The physical separation of solvent particles (d) None of the above

How could you make water boil at \(20^{\circ} \mathrm{C}\) (approximately room temperature)?
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