In a laboratory experiment, a 10.0-mL sample of NaCl solution is poured into an evaporating dish with a mass of 24.10 g. The combined mass of the evaporating dish and NaCl solution is 36.15 g. After heating, the evaporating dish and dry NaCl have a combined mass of 25.50 g. (9.4)b. What is the molarity (M) of the NaCl solution?

Verified step by step guidance

1. Calculate the mass of the NaCl solution by subtracting the mass of the empty evaporating dish from the combined mass of the dish and solution: \(36.15\, \text{g} - 24.10\, \text{g}\).
2. Determine the mass of the dry NaCl by subtracting the mass of the empty evaporating dish from the combined mass of the dish and dry NaCl: \(25.50\, \text{g} - 24.10\, \text{g}\).
3. Calculate the mass of water that was evaporated by subtracting the mass of the dry NaCl from the mass of the NaCl solution.
4. Convert the mass of dry NaCl to moles using the molar mass of NaCl (approximately 58.44 g/mol).
5. Calculate the molarity (M) of the NaCl solution by dividing the moles of NaCl by the volume of the solution in liters (10.0 mL = 0.010 L).

Key Concepts

Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. It is calculated using the formula M = moles of solute / liters of solution. Understanding molarity is essential for determining how concentrated a solution is, which is crucial in various chemical reactions and laboratory procedures.

Mass and Moles Relationship

The relationship between mass and moles is governed by the molar mass of a substance, which is the mass of one mole of that substance in grams. To find the number of moles, you can use the formula: moles = mass (g) / molar mass (g/mol). This concept is vital for converting the mass of NaCl in the solution to moles, which is necessary for calculating molarity.

Evaporation and Solute Recovery

Evaporation is the process of turning a liquid into vapor, which can be used to separate a solute from a solvent. In this experiment, heating the NaCl solution causes the water to evaporate, leaving behind dry NaCl. Understanding this process helps in determining the amount of solute present after evaporation, which is needed to calculate the initial concentration of the solution.