CBSE Chemistry Experiment Viva Questions with Answers on Determination of Boiling Point

The boiling point (b.p.) of a liquid is defined or described as the temperature at which the pressure or vapour pressure of the same liquid is equal to the atmospheric pressure exerted or applied on the surface of the liquid. Pressure cookers are the most common example of boiling in our everyday life. Also, boiling water makes it pure and filtered without filtration methods like charcoal treatment, filter paper, etc.

Table of Content

1. Aim

2. Materials Required

3. Theory 

4. Procedure

5. Observations

6. Result

7. Precautions

Aim

To determine the boiling point of the given substances and also create viva questions and answers for this.

Materials Required

1. Thermometers, (Celsius scale)

2. Boiling tube

3. A glass rod

4. Iron stand 

5. A Bunsen burner 

6. Wire gauze

7. Beakers

8. Tripod Stand

9. Distilled water

Theory

1. Boiling Point 

The temperature at which the liquid boils and changes into a gaseous state at atmospheric pressure is called the boiling point. For example, water boils at 100 °C to form water vapour (at 76 cm pressure).

2. Latent Heat of Vapourization 

The heat energy absorbed by the water when it changes its phase to steam, this hidden heat, is called the latent heat of vapourization.

Procedure

1. Take 25-30 ml of water in a boiling tube and add a few pumice stones to it.

2. Clamp the boiling tube on an iron stand with two holed corks, in one hole fix the thermometer and in the other one fix the delivery tube.

3. Place the thermometer above the water in the flask as shown in the figure and record its temperature.

4. Place a burner under the boiling tube.

5. Read the temperature and record it in the given observation table till the water boils. Record the reading after the time interval of 1 minute.

Set-up of the Apparatus

Observations

Result

• The boiling point of water is 100 °C.

• Once the boiling point is attained, the temperature reading on the thermometer does not change for some time.

Precautions

1. Choose a better quality thermometer whose graduated scale is readable.

2. Record the temperature in whole numbers.

3. While reading the thermometer, the eye level should be parallel with the mercury level.

4. Dip only the bulb of the thermometer into water/ice.

5. The thermometer should not touch the walls of the beaker or boiling tube.

Lab Manual Questions

1. For proper reading, what should be the position of the thermometer bulb and ignition tube?

Ans. For proper reading, the thermometer bulb and the ignition tube (lower end) should be placed at the same level.

2. The sharp boiling point of crystalline solids is due to the___________.

Ans. Crystalline solids have a sharp boiling point because all the components of the crystalline solid are present at the same or equal distance from each other.

3. Which metal block has been used in this experiment?

Ans. An aluminium block has been used in this experiment.

4. The boiling point of a pure substance is sharp because of the__________.

Ans. The boiling point of a pure substance is sharp because pure substances exhibit very well-defined physical properties or properties that are not connected with the substance’s ability to combine with the different substances.

Viva Questions

1. Define boiling point.

Ans. The boiling point may be defined as the temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure.

2. On increasing pressure, how does the boiling point gets affected?

Ans. On increasing the outside pressure, the boiling point of the liquid increases.

3. What is the effect of a decrease in pressure on the boiling point?

Ans. On decreasing the outside pressure, the boiling point of the liquid decreases.

4. What will happen to the boiling point of the liquid if some non-volatile liquid is added to it?

The boiling point of the liquid will increase.

5. Why do different liquids have different boiling points?

The boiling point depends upon intermolecular forces existing in the liquid. Since different liquids have intermolecular forces of different strengths, therefore their boiling points are different.

6. Why is food cooked more quickly in a pressure cooker?

In a pressure cooker, water boils at a higher temperature and hence cooking takes place at a higher temperature.

7. Suppose the boiling point of a liquid is 100 °C in Kolkata. At the hill station will it be the same or different? Give reasons.

The boiling point of the liquid will be less than 100 °C at the hill station. The boiling point decreases with a decrease in atmospheric pressure. At hill stations, the atmospheric pressure is less than that in plains.

8. Why do carboxylic acids have a higher boiling point than hydrocarbons?

Ans. The carboxylic acid can form hydrogen bonding, and these hydrogen bonds stabilize the complete molecule, enabling the organic chain to form additional bonds by dispersion forces.

9. Define the effect of impurity on boiling point.

Ans. Impurities increase the boiling point. This is due to the reason that it stabilizes the liquid phase and makes it more energetically favourable.

10. At what temperature is the density of water maximum?

Ans. At 4 °C, the density of water is maximum.

Practical Questions

1. The boiling point of pure water is-

1. 0 ℃

2. 100 F

3. 100 ℃

4. None of these

Ans. The boiling point of water or pure water is 100 ℃.

2. What is happening at the boiling point

1. Liquid to gas

2. Solid to liquid

3. Gas to liquid

4. Liquid to solid

Ans. At boiling point, liquid changes or converts into gas.

3. The boiling point of water in hilly regions?

1. Less than 100 ℃

2. Equal to 100 ℃

3. Greater than 100 ℃

4. None of these

Ans. In a hilly region, the boiling point of water is less than 100 ℃.

4. How does the boiling point relate to atmospheric pressure?

1. Directly proportional

2. Indirectly proportional

3. Not related

4. None

Ans. The boiling point and atmospheric pressure are directly proportional to each other.

5. The boiling point of water at sea level is-

1. 99 ℃

2. 100 ℃

3. 103.7 ℃

4. 273 ℃

Ans. At sea level, the boiling point of water is 100 ℃.

6. How does the boiling point get affected by the molecular weight?

1. It decreases with an increase in molecular weight.

2. It increases with an increase in molecular weight.

3. It increases with a decrease in molecular weight.

4. Does not get affected

Ans. The boiling point increases with an increase in molecular weight.

7. Which of the following possesses the highest boiling point?

1. Butane

2. Methane

3. Propane

4. Pentane

Ans. Pentane has the highest boiling point of all.

8. How is the boiling point impacted by the hydrogen bonding?

1. Decreases with an increase in hydrogen bonding.

2. Increases with an increase in hydrogen bonding.

3. Increases with a decrease in hydrogen bonding.

4. Having no effect on hydrogen bonding.

Ans. The boiling point increases with an increase in hydrogen bonding.

9. Camphor is used in molecular mass determination because

1. It has a very high cryoscopic constant

2. It is volatile

3. It is readily available

4. It is a solvent for organic substances

Ans. Camphor is used in molecular mass determination because it is volatile.

Conclusion

From the above experiment, we learned to determine the boiling point of water. We can conclude that the boiling point of water is 100 °C. Once the boiling point is attained, the temperature reading on the thermometer does not change for some time.