Page 144 - Chemistry_Form_2

Chemistry
for Secondary Schools

Activity 5.14

Aim: To investigate the action of heat on sodium sulfate and iron(II) sulfate

Requirements: Ignition tube, spatula, heat source, sodium sulfate, iron(II)
FOR ONLINE READING ONLY
sulfate, and red and blue litmus papers
Procedure

1. Put a spatulaful of sodium sulfate in the ignition tube and heat strongly.
2. Insert the wet blue and red litmus papers in the ignition tube while heating.
Record the observations.

3. Repeat Steps 1 and 2 by using iron(II) sulfate in the place of sodium sulfate.
Record the observations.

Questions
1. What were the colour changes in the two litmus papers?

2. What do the colour changes in the litmus papers imply?

Action of heat on chloride salts
All chloride salts except ammonium chloride do not decompose on heating.
Ammonium chloride on heating, sublimes and decomposes to ammonia gas and
hydrogen chloride gas.

Deliquescence, hygroscopy, and efflorescence in salts
Based on their behaviour when exposed to air, salts are categorised as deliquescent,
hygroscopic or efflorescent.

Deliquescent salts

A salt that absorbs moisture from the air (environment) to form a solution is
called a deliquescent salt. Examples of deliquescent salts are sodium hydroxide,
phosphorus oxides, potassium hydroxide, and calcium chloride.

Hygroscopic salts
A hygroscopic salt is the one which absorbs water from air without necessarily
forming a solution. Examples of hygroscopic salts are sodium chloride, sodium
nitrate, calcium chloride, calcium oxide, and copper sulfate. The tendency of

Student’s Book Form Two 137

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 137