Textbook Question
An aqueous NaCl solution is made using 102 g of NaCl diluted to a total solution volume of 1.00 L. Calculate the molality of the solution. (Assume a density of 1.08 g>mL for the solution.)
14. Solutions
Molality
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A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25°C. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. What is the molality of the methanol in the solution?
A
0.150 mol/kg
B
0.220 mol/kg
C
0.200 mol/kg
D
0.171 mol/kg
Verified step by step guidance1
Calculate the mass of methanol using its volume and density. Use the formula: mass = volume × density. For methanol, this is: mass = 20.2 mL × 0.782 g/mL.
Calculate the mass of water using its volume and density. Use the formula: mass = volume × density. For water, this is: mass = 100.0 mL × 1.00 g/mL.
Convert the mass of methanol to moles. Use the molar mass of methanol (CH3OH), which is approximately 32.04 g/mol. Use the formula: moles = mass / molar mass.
Calculate the molality of the methanol in the solution. Molality is defined as moles of solute per kilogram of solvent. Use the formula: molality = moles of methanol / mass of water in kg.
Ensure the mass of water is converted from grams to kilograms by dividing by 1000, as molality is expressed in moles per kilogram of solvent.
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