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 melting point (Class 11 chemistry practical)

You pack a capillary melting-point tube and heat it slowly until the solid melts.

The compound name and literature value come from your manual — record your observed range only.

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.

Hot oil and glass.
Some solids are irritant — use assigned sample only.

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 melting point (or melting range) of a solid sample assigned in your laboratory manual using a melting-point tube and suitable heating arrangement.

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

Apparatus and chemicals

Apparatus and chemicals
Item	Note
Melting-point capillary	Fine bore, sealed at one end.
Melting-point apparatus or Thiele tube / oil bath	As your school uses.
Thermometer	Calibrated; read as your manual describes.
Spatula and watch glass	For loading the capillary.
Bunsen burner or electric heater	Teacher-controlled heating rate.
Assigned solid (e.g. benzoic acid, naphthalene) (solid 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 tubes and apparatus for melting-point determination — Pack the capillary evenly and heat slowly near the expected melting range. Record the temperature range you actually observe.

Theory and reaction

Open

Pure crystalline solids melt sharply at a fixed temperature (at atmospheric pressure). Impurities usually lower and broaden the melting range.

Heat slowly near the expected melting point so the thermometer and sample stay in thermal equilibrium.

Record the temperature when melting begins and when it is complete — your manual may call this the melting range.

Phase change at characteristic temperature; no balanced chemical equation for a simple melting-point determination.

Procedure

Powder a small amount of the solid finely on a watch glass. Dry if your manual says the sample must be anhydrous.
Tap the open end of the capillary into the powder until a 2–3 mm column sits in the tube (depth as your manual states).
Pack the column evenly by dropping the sealed end through a short glass tube or using the apparatus packing tool.
Insert the capillary in the melting-point apparatus with the thermometer bulb level with the sample.
Heat steadily. Note the temperature when the first liquid appears and when melting is complete.

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.	Melting begins (°C)	Melting complete (°C)	Range (°C)
1
2
3

Calculation

Melting range = (completion temperature − start temperature). Compare qualitatively with the literature value your manual prints — do not invent a literature number here.

Result

Write the melting range you observed and the sample name. Leave comparison blank if your teacher collects readings separately.

Precautions

Heat slowly near the melting point — fast heating gives high readings.
Use a dry sample if moisture depresses the point.
Do not overfill the capillary.
Hot oil and burners — follow your teacher’s setup.

Viva questions

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

Question 1 of 4

Impurities in a solid generally…

A. Raise and sharpen the melting pointB. Lower and widen the melting rangeC. Have no effectD. Make the solid sublime always

Pick an answer first.

Show all questions and answers

Impurities in a solid generally…
Answer: Lower and widen the melting range. Reason: Impurity disrupts the lattice → lower, broader melting.
Why heat slowly near the melting point?
Answer: So the thermometer reading matches the sample temperature. Reason: Thermal lag gives false high readings if heating is fast.
Melting-point capillary is packed with…
Answer: A short column of finely powdered solid. Reason: A small packed column melts in the hot zone.
Melting point is a useful purity check because…
Answer: Pure compounds melt over a narrow range near a tabulated value. Reason: Sharp melting near literature value suggests purity.

Common mistakes

Large unfilled air gaps in the capillary → wrong temperature.
Heating too quickly.
Thermometer bulb not level with the sample.
Copying a literature melting point instead of your observed range.

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.

Report an error