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CHEMISTRY FORM 1


i Common Chemistry Laboratory Chemicals
ii Common Chemistry Laboratory Apparatus
iii Safety in the Chemistry Laboratory
iv Why we should learn Chemistry
1. INTRODUCTION TO CHEMISTRY
2. SIMPLE CLASSIFICATION OF SUBSTANCES AND SEPERATION OF MIXTURES
3. ACIDS, BASES AND INDICATORS
4. AIR AND COMBUSTION
5. WATER AND HYDROGEN
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Simple Classification of Substances and Separation of Mixtures: Permanent and non-permanent changes

2.0 Simple Classification of Substances and Separation of Mixtures


2.15 Permanent and non-permanent changes


What is a permanent change?


Observe a mixture of sulphur and iron filings, and check whether they can be separated using a magnet.

(Courtesy Youtube - Iron + Sulphur by Scott Milam)
In this demonstration, iron is represented by Fe, and sulphur by S.



Questions 2.15(a)

    1. What is the color of sulphur and of iron? Sulphur ---Iron ---
    2. Can the mixture be separated using a magnet?
  1. The following set-up can be used to study the action of iron on sulphur and vice versa.
    Set-up seperating iron and sulphur high school chemistry


    1. Observe and report what happens during strong heating of a mixture of iron filings and sulphur.
      (Courtesy Youtube - Iron + Sulphur by Scott Milam) (5g of iron and 3 g of sulphur mixed well) held in an ignition tube.
    2. What is the color of the product (when emptied onto a white tile)?
    3. Is the product attracted by a magnet anymore?

Answers to Questions 2.15(a)


These observations show that a new substance has been formed, whose color and other properties are quite different from those of the original substances in the heated mixture. And it cannot be easily changed back (reversed) to the original substances. Such a change is a permanent change.


Permanent changes normally occur with release of heat (e.g. a glow).


effect of heat on copper (II) nitrate crystals high school chemistry

The set-up below shows an arrangement that can be used to study the effect of heat on copper (II) nitrate crystals.


Set-up effect of heat on copper (II) nitrate crystals high school chemistry

Watch the video, effect of heat on copper (II) nitrate crystals.


Questions 2.15(b)


    1. Describe the changes that occur when copper (II) nitrate crystals are heated strongly till no further change occurs.
    2. Is this a permanent or non-permanent change? Give a reason for your answer.
  1. Suggest a reason why
    1. the flame is moved over the test tube during heating.
    2. the experiment should be done in a fume chamber.

Answers to Questions 2.15(b)



There are many other cases of permanent change.
In permanent changes

  1. The change is not reversible.
  2. Heat is absorbed or released.
  3. A new substance is formed.
  4. Mass changes.

What is a non-permanent (temporary) change?


Questions 2.15(c)


    1. Observe iodine crystals and compare them with the sublimate (the solid formed when iodine vapor is cooled back to solid).
      (courtesy Youtube - DHS SEPERATING SAND IRON IODINE by Tyler Bruns ). How are they similar?
    2. Has the properties of iodine been changed by heating?
  1. Observe and report the colour of zinc oxide when it is hot and again when allowed to cool.
    (courtesy Youtube - Heating zinc oxide by DrMarkForeman. ) Is this a permanent or non-permanent change?
    1. Observe and report the changes that occur when hydrated copper (II) sulphate crystals are heated cooled then a drop of water is added to it.
      (courtesy Youtube - Heating of Copper Sulphate - MeitY OLabs by amritacreate )
    2. What happens when the residue is cooled then a drop of water is added to it?
    3. Is this a permanent or non-permanent change?
    4. What is the word equation for this change?
    1. Observe and report the changes that occur when hydrated cobalt (II) chloride crystals are heated, cooled then a drop of water added to them.
      (courtesy Youtube - Thermal Decomposition of Cobalt (II) Chloride Hexahydrate - by Yeo Yong Kiat )
    2. What happens when the residue is cooled then a drop of water is added to it?
    3. Is this a permanent of non-permanent change?
    4. Write the word equation for this change.

Answers to Questions 2.15(c)


When iodine is heated, no glow occurs. The shiny grey crystals turn into a purple vapour which cools back into grey crystals - similar to the original crystals, though finer. It is the same iodine; no new substance has been formed.


A change in which the original substance(s) is easily obtained back is called non-permanent change. Other examples of non-permanent change are:


  1. The change of colour from white to yellow then back to white when zinc (II) oxide is heated

  2. The change of hydrated copper (II) sulphate crystals from blue to white solid when heated and back to blue when water is added
     heating hydrated copper (II) sulphate crystals high school chemistry

  3. The change of hydrated cobalt (II) chloride crystals from pink to blue when heated and back to pink when water is added
    heating hydrated cobalt (II) chloride crystals high school chemistry

Examples 2 and 3 involve breaking down of a substance into simpler substances. The process is called thermal decomposition or thermal dissociation (because they are caused by heat). Thermal means, to do with heat.

Differences between non-permanent and permanent change


difference between non permanent and permanent change high school chemistry

At home

In a burning candle, the observed flame and soot represent permanent changes. Sweet potatoes, banana peels, and fried eggs turn black, and decompose on long exposure. These too are permanent changes. But the melt dripping from a burning candle solidifies back into wax; so melting is a non-permanent change.