1. 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.
g NaCl per 1.000kg H2O ÄTf . °C
5.845 0.348
0.585 0.0360
0.293
0.0182
2. A student determines the Kf of t-butyl alcohol using tap water instead of distilled or deionized water. Described the problem that might have been encounted. How would problems affect the magnitude of Kf?
If you have tabulated the data it isn't clear what you've posted.
For the second problem,
delta T alcohol = i*Kf*m
Kf = delta T/i*m
If you used tap water, which contains minerals, then i will be greater than 1 and Kf will be smaller than expected.
1. From the data provided, it is observed that as the amount of NaCl dissolved in the water increases, the freezing point depression (ΔTf) also increases.
The freezing point depression is directly proportional to the concentration of solute particles in a solution. When a solute, in this case NaCl, dissolves in a solvent, it breaks into individual ions (Na+ and Cl-) due to its ionic nature. These ions then interact with the water molecules, disrupting the regular formation of ice crystals and lowering the freezing point of the solution.
In the first sample, 5.845 g of NaCl is dissolved in 1.000 kg of water, resulting in a freezing point depression of 0.348 °C. This can be attributed to the higher concentration of solute particles, leading to more interactions with water molecules and a greater disruption of the freezing process.
In the second sample, 0.585 g of NaCl is dissolved in 1.000 kg of water, resulting in a lower freezing point depression of 0.0360 °C. This is due to the lower concentration of solute particles compared to the first sample, resulting in fewer interactions and a lesser disruption of the freezing process.
In the third sample, 0.293 g of NaCl is dissolved in 1.000 kg of water. This results in a freezing point depression of 0.0182 °C, which is even lower than the second sample. This is because the concentration of solute particles is further reduced, leading to fewer interactions and less disruption of the freezing process.
For a solution made up of 29.22 g of NaCl dissolved in 1.000 kg of water, we can predict that the freezing point depression will be higher compared to the first sample. This is because the higher concentration of NaCl will result in more solute particles and thus more interactions with the water molecules, leading to a greater disruption of the freezing process and a larger decrease in the freezing point.
2. Using tap water instead of distilled or deionized water can introduce impurities and other dissolved substances into the solution. These impurities can affect the accuracy and precision of the Kf (freezing point depression constant) determination for t-butyl alcohol.
Tap water often contains various minerals, ions, and other dissolved substances like chlorine or organic compounds. These impurities can interfere with the measurement of the freezing point depression and may result in inaccurate results. They can alter the colligative properties of the solution and affect the observed freezing point depression.
The magnitude of Kf represents the extent of freezing point depression caused by a given concentration of solute particles. If tap water with impurities is used in the experiment, these impurities may contribute to the overall freezing point depression, affecting the measurement of Kf. As a result, the calculated Kf value would be greater than the true value since it includes both the effect of the solute particles and the impurities.
To obtain accurate and reliable results for the magnitude of Kf, it is recommended to use distilled or deionized water, which has a known and controlled purity. This ensures that the freezing point depression is solely due to the solute particles and not influenced by impurities from the solvent.
1. In this experiment, the freezing point depression is being studied. Freezing point depression occurs when a solute, in this case NaCl, is dissolved in a solvent, which is water (H2O). The presence of the solute particles in the solvent lowers the freezing point of the solution compared to that of pure water, known as the freezing point depression.
The observed results show that as the amount of NaCl dissolved in water increases, the freezing point depression also increases. The freezing point depression is quantified by the change in temperature of freezing, which is denoted as ΔTf. In this case, the value of ΔTf is given in degrees Celsius.
By comparing the data, it can be observed that as the mass of NaCl per 1.000kg H2O increases, the value of ΔTf also increases. This is because the concentration of solute particles increases, leading to more significant interactions between the solute and solvent particles. These interactions disrupt the formation of the crystal lattice structure that occurs during freezing and result in a lower freezing point.
Based on the observed results, if 29.22 g NaCl is dissolved in 1.000kg H2O, we would expect a relatively higher value of freezing point depression (ΔTf) compared to the previous three solutions. This is because the higher amount of NaCl will increase the concentration of solute particles in the solution, leading to stronger interactions and a greater depression of the freezing point.
2. The problem encountered in using tap water instead of distilled or deionized water is that tap water contains impurities and dissolved minerals that can affect the determination of the Kf value. Distilled or deionized water is usually preferred in experiments because it is purified and does not contain any impurities or additional solutes.
The impurities and dissolved minerals present in tap water can alter the colligative properties of the solution, such as freezing point depression. This can lead to inaccurate Kf values. The magnitude of Kf, which represents the molal freezing point depression constant, may be affected by the impurities present in tap water.
Different impurities and minerals will have different effects on the solution properties, including the freezing point depression. This can result in variations in the observed Kf values. To obtain accurate results and compare them with established values, it is important to use a pure solvent, such as distilled or deionized water, to ensure minimal interference from impurities.