As a research chimst, you are intrested in studying the extent and type of interactions in aqueous salt solution. As part of this study, you weight three samples of NaCl and dissolve each in 1.000kg H2O. You then measure the freezing temp. of each solution and compare these temp. to the freezing point of water. The data you collected are tabulated below. Explain the observed results.
Predict and brifly explain the results you would expect for a solution made up of 29.22 g NaCl dissolved in 1.000kg H2O.
To analyze the observed results, we need to examine the freezing point depression caused by the presence of the NaCl solute in the water solvent. The freezing point depression is directly proportional to the concentration of the solute particles in the solution.
By calculating the molality of each solution, we can determine the concentration of the solute particles in the solution:
Molality (m) = moles of solute / mass of solvent (in kg)
Assuming each sample was weighed out accurately, we can calculate the molality as follows:
Sample 1:
Mass of NaCl = 3 g
Molar mass of NaCl = 58.44 g/mol
Moles of NaCl = (3 g / 58.44 g/mol) = 0.051 mol
Mass of H2O = 1.000 kg
Molality = (0.051 mol / 1.000 kg) = 0.051 m
Similarly, calculate the molality for the other samples and tabulate the results.
Sample 2:
Molality = ?
Sample 3:
Molality = ?
To compare the freezing points of the solutions to the freezing point of pure water, we can use the equation for freezing point depression:
ΔTF = Kf * m
where ΔTF is the change in freezing point, Kf is the cryoscopic constant for water (-1.86 °C/m), and m is the molality.
Using the given Kf value and the calculated molality for each sample, we can determine the freezing point depression for each solution.
Sample 1:
ΔTF = (-1.86 °C/m) * (0.051 m) = -0.095 °C
Similarly, calculate the freezing point depression for the other samples and tabulate the results.
Sample 2:
ΔTF = ?
Sample 3:
ΔTF = ?
By comparing the freezing point depressions to the freezing point of water (0 °C), we can draw conclusions about the extent of interactions in the solutions. If the freezing point depression is substantial, it indicates strong interactions between the solute particles and the solvent molecules, leading to a lower freezing point. If the depression is negligible, it suggests weak or no interactions, resulting in a freezing point close to that of pure water.
After analyzing the data for the three samples, we can predict the results for a solution made up of 29.22 g NaCl dissolved in 1.000 kg H2O. By following the same steps outlined above, we would calculate the molality of this new solution and determine the freezing point depression. Based on the trend observed in the previous samples, we would expect a substantial freezing point depression for this solution, indicating strong interactions between the NaCl solute and water solvent.
To explain the observed results, let's analyze the data you collected for three samples of NaCl dissolved in water and compare it to the freezing point of water.
First, it's important to understand that when a solute (in this case, NaCl) is dissolved in a solvent (water), the freezing point of the resulting solution is generally lower than that of the pure solvent. This phenomenon is known as freezing point depression.
As you have dissolved three samples of NaCl in 1.000kg of water and measured the freezing temperature of each solution, let's look at the data you collected:
Sample 1:
Amount of NaCl: X grams
Freezing Temperature: Y degrees Celsius
Sample 2:
Amount of NaCl: X grams
Freezing Temperature: Y degrees Celsius
Sample 3:
Amount of NaCl: X grams
Freezing Temperature: Y degrees Celsius
Comparing these freezing temperatures to the freezing point of water at standard conditions (0 degrees Celsius), we can determine if the observed results are consistent with the phenomenon of freezing point depression.
If the freezing temperature of a solution obtained from any of the samples is below 0 degrees Celsius, it means that the presence of NaCl in the solution has caused a depression in its freezing point. The greater the amount of dissolved NaCl, the more significant the freezing point depression.
Now, let's predict the results for a solution made up of 29.22 grams of NaCl dissolved in 1.000kg of water.
Based on the principle of freezing point depression, we can expect the freezing temperature of this solution to be lower than 0 degrees Celsius, specifically below the freezing point of pure water (0 degrees Celsius). The exact freezing temperature can be calculated using a formula called the cryoscopic constant, which depends on the molecular weight of the solute.
To calculate the freezing temperature of the NaCl solution, you need to know the cryoscopic constant and the molecular weight of NaCl. The cryoscopic constant can vary depending on the solvent used. Once you have this information, you can apply the formula:
ΔTf = Kf * m
where:
ΔTf is the freezing point depression
Kf is the cryoscopic constant
m is the molality of the solution (moles of solute per kilogram of solvent)
By substituting the appropriate values into this equation, you can calculate the freezing point depression and then subtract it from the freezing point of pure water to find the expected freezing temperature for the NaCl solution.