Question

How much would the boiling point of water increase if 4 mol of NaCl were added to 1 kg of water (Kb = 0.51 oC/(mol/kg) for water and i = 2 for NaCl)?

a) 1.02 oC

b) 2.04 oC

c) 0.51 oC

d) 4.08 oC

Answer 1

The boiling point of water will increase by 4.08 oC when 4 mol of NaCl are added to 1 kg of water, using the molal boiling point elevation constant for water and considering the van't Hoff factor for NaCl.

Step-by-step explanation:

To calculate the boiling point elevation caused by adding NaCl to water, we use the boiling point elevation formula: ∆Tb = i * Kb * m, where ∆Tb is the change in boiling point, i is the van't Hoff factor, Kb is the molal boiling point elevation constant, and m is the molality of the solution. For NaCl, i = 2 because it dissociates into two ions (Na+ and Cl−), Kb for water is 0.51 oC/(mol/kg), and the molality is 4 mol/kg since 4 mol of NaCl are added to 1 kg of water.

Using this information: ∆Tb = 2 * 0.51 oC/(mol/kg) * 4 mol/kg = 4.08 oC. Thus, the boiling point of water will increase by 4.08 oC. The answer is option d) 4.08 oC.