Introduction

Freezing point depression is a phenomenon that occurs when a solute is added to a solvent, causing its freezing point to lower. In this practical investigation, we will explore the freezing point depression of water with different concentrations of sodium chloride (NaCl) and measure its impact on the freezing point. The experiment will involve preparing 50ml solutions of sodium chloride in water and measuring the temperature when the solution freezes over a range of salt concentrations from 1g to 20g per litre.

Materials

• Sodium chloride (NaCl)
• Water
• 50ml beakers
• Electronic balance
• Digital Thermometer
• Ice bath (50g NaCl per litre of water)
• Stirring rod
• Safety goggles

Safety Precautions

• Wear safety goggles throughout the experiment to protect your eyes from any potential harm.

Method

1. Weigh a clean, dry 50ml beaker and record its mass.
2. Calculate the mass of sodium chloride required to make the different solutions 1g to 20g per litre. Add the known mass of sodium chloride to the beaker and weigh the beaker again to determine the mass of the salt.
3. Add 50ml of water to the beaker and stir with a stirring rod until the salt dissolves completely.
4. Place the beaker in an ice bath and stir the solution with the stirring rod.
5. Record the temperature of the solution every 30 seconds using a digital thermometer until it begins to freeze. Stir the solution constantly to ensure the temperature is consistent throughout.
6. Record the lowest temperature reached by the solution before it freezes. This is the freezing point of the solution.
7. Repeat steps 1-6 for different concentrations of sodium chloride in the water, ranging from 1g to 20g per litre.

Independent Variable

The independent variable in this investigation is the concentration of sodium chloride in the water. We will measure the freezing point depression of water at different concentrations of sodium chloride ranging from 1g/L to 20g/L.

Dependent Variable

The dependent variable in this investigation is the freezing point of the sodium chloride solution. We will measure the temperature when the solution freezes and record the lowest temperature reached before it freezes.

Data Collection

Record the mass of the beaker before and after adding the salt and the volume of water used. Record the temperature of the solution every 30 seconds until it begins to freeze and record the lowest temperature reached before it freezes.

Concentration of Salt (g/L)	Mass of Salt Added (g)	Volume of Water (mL)	Freezing Point (°C)
1		50
2		50
3		50
4		50
5		50
10		50
15		50
20		50

Data Analysis

Create a table of the recorded temperatures for each concentration of sodium chloride and calculate the freezing point depression using the formula: Freezing Point Depression (°C) = Freezing Point of Pure Water (0°C) – Freezing Point of Solution (°C)

Plot a graph of the freezing point depression against the concentration of sodium chloride to determine the relationship between the two variables.

Conclusion

Write a conclusion and evaluation for the investigation.

• Trends: Identify any trends in the data collection.
• Relevance: Does the conclusion address the research question or hypothesis that was posed at the beginning of the investigation?
• Consistency: Are the conclusions consistent with the data and observations that were collected during the investigation?
• Accuracy: Are the conclusions supported by the evidence presented in the investigation? Are the conclusions based on reliable and valid data?
• Completeness: Does the conclusion provide a comprehensive summary of the investigation and the results obtained? Are all the relevant aspects of the investigation covered?
• Significance: Are the conclusions significant and meaningful in the context of the research question or hypothesis? Do they contribute to the body of knowledge in the field?
• Limitations: Are the limitations of the investigation discussed? Are the conclusions limited by the scope or methodology of the investigation?
• Recommendations: Are any recommendations made for future research or for the application of the results obtained?

• Practical Chemistry
• Practical Physics