Effect of Impurities on Boiling Point and Freezing Point

Abstract

This experiment investigates the impact of impurities on the boiling point and freezing point of a liquid, in this case, water. The boiling point and freezing point are fundamental properties of liquids and can be affected by the presence of solutes. The experiment aims to observe and measure the changes in these properties as the concentration of impurities (glucose) in the water increases. The results will provide insights into the colligative properties of solutions and how they depend on the number of moles of solute rather than the nature of the solute.

Introduction

Boiling point and freezing point are two important temperature parameters for any liquid substance. The freezing point is the temperature at which a liquid turns into a solid at a constant temperature, while the boiling point is the temperature at which a liquid turns into a vapor or gas and escapes into the atmosphere. For water, the freezing point is 0°C or 273 K, and the boiling point is 100°C or 373 K under normal atmospheric pressure.

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In terms of vapor pressure, the boiling point of a liquid is the temperature at which the vapor pressure of the liquid becomes equal to the atmospheric pressure. Similarly, the freezing point is the temperature at which the solid and liquid phases of a substance have the same vapor pressure.

When impurities are introduced into a liquid, they can have a significant impact on its boiling and freezing points. The presence of impurities tends to alter the temperature at which phase transitions occur.

Specifically, when impurities are added, the freezing point of the liquid is lowered, while the boiling point is elevated.

This phenomenon occurs because the impurities reduce the vapor pressure of the solution, making it harder for the liquid to transition into the vapor phase (boiling) or for the solid to form (freezing). As a result, more energy is required to reach the boiling point or freezing point, leading to changes in these temperature values.

In this experiment, we will explore the effect of impurities, specifically glucose, on both the freezing point and boiling point of water. We will vary the concentration of glucose in the water and observe how these colligative properties change in response to the number of moles of solute present.

Experiment No.1 - Effect on Freezing Point

AIM:

To determine the effect of impurities on the freezing point of water.

APPARATUS REQUIRED:

• 500 ml beaker
• Boiling tubes
• 110°C thermometer with 0.1°C calibration
• Cork
• Iron stand
• Stirrer

MATERIAL REQUIRED:

• Glucose
• Ice
• Water
• KNO3 (Potassium Nitrate)

PROCEDURE:

1. Take three clean and dry boiling tubes and label them as 1, 2, 3.
2. Take 20ml of distilled water in each boiling tube.
3. Add 1g of glucose to boiling tube no. 2 and 2g of glucose to boiling tube no. 3. Shake until the glucose is dissolved.
4. Put a mixture of ice and KNO3 in a beaker and fix test tube no. 1 in it. Insert a thermometer in a bored cork and fix it in a stand so that its bulb dips in water in boiling tube no. 1.
5. Stir the water in boiling tube no. 1 and observe the temperature as it gradually falls. Note the temperature when it remains constant, indicating that the water has started freezing. This is the freezing point of pure water.
6. Remove boiling tube no. 1 from the beaker and replace it with boiling tube no. 2. Repeat the experiment and note the freezing point of the glucose solution (which is 5% since 1g is dissolved in 20ml of water).
7. Now place boiling tube no. 3 in position and repeat the experiment to note its freezing point (10% glucose).

RESULT:

The freezing point of water decreases due to the presence of dissolved glucose. Additionally, the depression in the freezing point increases as the quantity of dissolved glucose increases.

Experiment No.2 - Effect on Boiling Point

AIM:

To determine the effect of impurities on the boiling point of water.

APPARATUS REQUIRED:

• Three boiling tubes each fitted with a cork with two holes
• 110°C thermometer with 0.1°C calibration
• Sand bath
• Burner
• Iron stand

MATERIAL REQUIRED:

• Glucose
• Water

PROCEDURE:

1. Take three clean and dry boiling tubes, each fitted with a cork with two holes (one for the thermometer and the other for a delivery tube).
2. Take 20ml of distilled water in each boiling tube.
3. Add 1g of glucose to boiling tube no. 2 and 2g of glucose to boiling tube no. 3. Shake until the glucose is dissolved.
4. Fit boiling tube no. 1 with a thermometer, keeping its bulb above the level of water. Fit it with a delivery tube and place it in an iron stand. Start heating it on a sand bath.
5. Heat the water and monitor the temperature as it gradually rises. Note the temperature when it becomes constant, indicating that the water has started boiling. This is the boiling point of pure water.
6. Fit boiling tube no. 2 in the same manner as described above and heat it. Note the boiling point of the 5% glucose solution.
7. Similarly, note the boiling point of the 10% glucose solution.

RESULT:

The boiling point of water increases due to the presence of dissolved glucose. Furthermore, the elevation in the boiling point increases as the quantity of dissolved glucose increases.

Discussion

Boiling Point & Freezing Point as Colligative Property

The changes in boiling point and freezing point observed in these experiments are examples of colligative properties. Colligative properties depend on the number of moles of solute particles in a solution rather than the nature of the solute itself. These properties include boiling point elevation and freezing point depression.

Application of Depression in Freezing Point

One practical application of depression in freezing point is in antifreeze solutions used in vehicles. When an appropriate amount of a suitable solute, usually ethylene glycol, is dissolved in water, the freezing point of the mixture is lowered. This property prevents the radiator from freezing in sub-zero temperatures, allowing vehicles to operate even in cold weather conditions.

Effect of Impurities on Freezing Point

When impurities are introduced into a liquid, such as water, its freezing point is lowered, meaning the liquid will freeze at a lower temperature than it would in its pure form. This depression in freezing point increases as the concentration of the solute or impurity increases. For example, when 1 mole of any non-electrolyte is dissolved in 1 liter of water, the depression in the freezing point of water is approximately 1.86°C.

Conclusion

In conclusion, the presence of impurities in a liquid affects its freezing and boiling points. The freezing point is lowered, and the boiling point is elevated when impurities are added. The degree of depression in the freezing point and elevation in the boiling point is directly proportional to the concentration of the solute or impurity. These changes in temperature are colligative properties and depend on the number of moles of solute particles in the solution. These properties are independent of the nature of the solute itself.

Recommendations

To further explore the effect of impurities on the boiling and freezing points, additional experiments with different solutes and concentrations could be conducted. Additionally, precise measurements and accurate temperature control are essential to obtain reliable results. Further research into practical applications of these colligative properties, such as antifreeze solutions, can also be explored.