When you are given the question: Arrange the following aqueous solutions in order of increasing boiling points. 0.050 m Mg(NO3)2; 0.100 m ethanol; and 0.090 m NaCl.
I know the formula for boiling point, but I don't know where to get the Kb. Am I headed in the right direction?
Actually you don't need Kb, although it is 0.51 degrees/molal for water. Look at the formula which is delta T = i*Kb*m
i is the number of particles. m is the molality, Kb is a constant.
So look at the product of i*m and see which is larger. As i*m*Kb increases, delta T increases and the boiling point increases. Since you are interest ONLY in the order, and not the exact boiling point, Kb doesn't matter.
Mg(NO3)2 has 3 particles; i.e., 1 Mg and 2 nitrate ions.
NaCl has 2 particles; i.e., 1 Na and 1 Cl^-. Etc.
Yes, you are headed in the right direction! The formula for boiling point elevation is ΔT = Kb * m * i, where ΔT is the change in boiling point, Kb is the molal boiling point elevation constant, m is the molality of the solute, and i is the number of particles the solute dissociates into in solution.
To determine the order of increasing boiling points, you need to compare the molalities (m) of the given solutions and consider the number of particles each solute forms in solution (i).
However, in your question, you are specifically asking about the constant Kb. The value for Kb depends on the solvent being used, not the solute. For example, the Kb value for water is different than the Kb value for a different solvent like ethanol.
To find the Kb value for a specific solvent, you can refer to a handbook or a reliable chemical database. These resources provide a comprehensive list of physical and chemical properties of various substances, including the Kb values for different solvents.
Alternatively, your instructor or textbook may provide you with the Kb value for a specific solvent, especially if it is a common one like water. In the absence of explicit information, assume the solvent is water and use the Kb value for water, which is approximately 0.512 °C/m.
Remember, it's essential to have the correct Kb value to accurately calculate the change in boiling points and compare the solutions in order.
Yes, you are headed in the right direction. The boiling point of a solution depends on the concentration of solute particles in the solution. The formula for boiling point elevation is given by:
ΔTb = Kb * m * i
ΔTb is the change in boiling point, Kb is the molal boiling point elevation constant, m is the molality of the solute, and i is the van't Hoff factor, which represents the number of particles formed when the solute dissolves.
In order to compare the boiling points of the given solutions, you need to consider the molality of each solute and the van't Hoff factor. In this case, we can assume that each solute completely dissociates in water, so the van't Hoff factor for all the solutes will be the number of ions produced when the compound dissolves.
Now, to determine the specific values of Kb for each solute, you need to consult reference materials or textbooks that provide the molal boiling point elevation constants for different solvents. The values of Kb depend on the specific solvent and are usually given in units of ΔTb per molal concentration (ΔTb/molality).
Once you have the values of Kb for each solute, you can use the formula to calculate the change in boiling point (ΔTb) for each solution. By comparing these values, you can then arrange the solutions in order of increasing boiling points.
I hope this clarifies your understanding. Let me know if you have any further questions.