CBSE Class 11 chemistry · purification and characterisation · Preparation and purification

Source: CBSE Class 11 chemistry practical syllabus · use your school laboratory manual (NCERT Lab Manual where your school uses it).

Determination of boiling point (Class 11 chemistry practical)

You observe the temperature at which a liquid boils steadily under the conditions your manual specifies.

Liquid identity and any correction for barometric pressure come from your teacher and manual.

Published practice page. Concentrations, masses, and numerical answers come from your school laboratory manual and your own readings — not invented here. Not yet reviewed by a named chemistry reviewer. Version 1.0.0, updated 2026-10-03.

Safety — read before you start

Safety warning. Practise here. Perform the real experiment only in your school lab, with your teacher present.

Flammable vapours.
Hot glass and burns.

Wear: Lab coat, Splash goggles, Gloves, as your teacher directs.

Follow your teacher’s disposal instructions. Do not pour leftovers down a household drain.

Loads only after you tap. Use the lab hands to pick up and use equipment (pointer hidden in the scene). Falls back to a flat diagram if WebGL is unavailable.

Aim

To determine the boiling point of a liquid sample provided in your laboratory manual using the apparatus your school specifies.

Methods and quantities can differ between schools. Follow your teacher's instructions.

Apparatus and chemicals

Apparatus and chemicals
Item	Note
Boiling-point tube or distillation flask	Micro method or small-scale distillation as directed.
Thermometer	Bulb in the vapour stream, not dipped in liquid only, for distillation method.
Bunsen burner or heating mantle	Controlled heating.
Capillary sealed at one end (Siwoloboff method)	If your manual uses the micro method.
Clamp stand	Secure hot glassware.
Assigned liquid (e.g. ethanol, acetone, water) (liquid sample)	Use the concentration, mass, volume, and sample names printed in your school laboratory manual. This page does not invent numerical results for you.

Test tube setup for boiling-point determination of a liquid — Heat gently with the thermometer bulb in the vapour (as your manual shows). Record the steady temperature for your liquid sample.

Theory and reaction

Open

At the boiling point, vapour pressure of the liquid equals the external pressure. Bubbles form throughout the bulk liquid.

Impurities usually raise the boiling point of a solvent (colligative effect) or change the observed plateau if the sample is a mixture.

In the micro capillary method, air in the capillary escapes as bubbles; when bubbling stops and the liquid enters the capillary, read the temperature as the boiling point (as your manual defines).

Phase change at characteristic temperature under stated pressure.

Procedure

Measure the small volume of liquid your manual specifies into the boiling-point tube or flask.
For the capillary method: insert a sealed capillary, heat until brisk bubbling, then continue heating slowly until liquid rises in the capillary and note the temperature.
For distillation-style setup: heat until distillation begins; record the steady temperature of the vapour at the thermometer bulb when drops form at a regular rate.
Note laboratory barometric pressure if your manual asks for a correction.
Allow apparatus to cool before disassembly.

Observation table

Enter the readings from your school lab in the practical file below. This page does not fill them in for you.

Type the readings in your practical file

S. No.	Liquid (—)	Boiling point observed (°C)	Room pressure (if recorded) (mm Hg / hPa)
1
2
3

Calculation

If your manual gives a barometric correction formula, apply it to your reading. Do not paste a textbook boiling point as your result.

Result

State the boiling point you observed, the liquid name, and pressure if recorded.

Precautions

Flammable liquids — no open flame near spilled solvent.
Point the outlet away from people.
Do not overfill micro tubes — bumping and spray.
Thermometer placement must match the method in your manual.

Viva questions

Answer one question at a time. The full answers stay closed until you open them.

Question 1 of 4

A liquid boils when…

A. Its density is 1 g mL⁻¹B. Its vapour pressure equals the external pressureC. It freezesD. It turns purple

Pick an answer first.

Show all questions and answers

A liquid boils when…
Answer: Its vapour pressure equals the external pressure. Reason: Boiling is a bulk vapour-pressure phenomenon.
Boiling point is useful for identifying a liquid because…
Answer: Pure liquids boil at a characteristic temperature at a given pressure. Reason: Characteristic bp helps identify pure liquids.
In simple distillation the thermometer bulb should sit…
Answer: At the level of the vapour at the side arm / distillation head. Reason: Vapour temperature defines the boiling point reading.
Many school boiling-point liquids are…
Answer: Flammable — keep away from stray flames and sparks. Reason: Ethanol, acetone, etc. need flame care.

Common mistakes

Reading the temperature before a steady boil plateau.
Thermometer dipped in liquid instead of vapour (distillation method).
Confusing initial air bubbles in the capillary with true boiling.
Inventing a corrected boiling point without your measured reading.

Frequently asked questions

Can I do this at home?: No. Use this page to practise the order of steps and viva. Do the real experiment only in your school laboratory, with your teacher present.

Your practical file

Name, school, and roll number are optional and are not sent anywhere.

The practical file opens on this device.

Review

Not yet reviewed by a named chemistry reviewer. Published for practice only — follow your teacher and laboratory manual for quantities and safety.

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