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Differentiating Between Salts III (Answers)

Differentiating Between Salts III

This is an online activity based on the previous two videos in the series:

Differentiating Between Salts I: https://youtu.be/mzK64GLq1wI

Differentiating Between Salts II

This video is a basic visual demonstration of the difference in colour between iron(II) and iron(III) salts.

Iron(II) salts are typically green in colour.

Differentiating Between Salts I This video is a basic visual demonstration of the difference in colour between iron(II) and copper(II) salts.

It is easy to mistake copper(II) carbonate for an iron(II) salt because most iron(II) salts are usually green in colour.

However, copper(II) carbonate is characteristically dry and powdery, while iron(II) salts are usually crystalline and shiny.

Dear 5A1,  It was a wet rainy day in December 2014 when I came back to Juying Secondary to pack and clear my table for the new academic year. I heard footsteps. I heard that only 10 students were returning to Juying for their Secondary 5NA experience. Unfortunately, I had already prepared 6 months worth of worksheets, each of which I had made 40 copies because I was expecting a full class. Such is the naivety of a young teacher. I first learnt from my HOD that I would be taking over your class from Ms Yang Wenqing, and I was worried. I was worried that I would not be able to foster the rapport and relationship that would be critical for your O Levels preparation. I know that Secondary 5 students undergo an immense amount of stress, and I spent my holidays speaking to my friends who went through the Secondary 5 experience. I hope that my candidness and my jokes have cheered you up throughout your academic year. I spoke to Ms Yang continuously about the five of you, because I knew that time wasn’t on my side when it came to knowing your character, personality and habits.

You have been the most obedient class out of all my classes in 2015. Not even once have I shouted at you. Not even once did I have to deal with discipline issues. I like many things about you. I like how all of you celebrated Raihan’s birthday - that day, I know some of you weren’t the happiest, but you got together for your friend’s sake. I like how you stuck together and created a class spirit - that’s the way friends should be. It doesn’t matter if you cried truckloads, or if you failed many times along the way. As long as you learn to pick yourself up again and again, then Juying has taught you the most precious lesson possible in life.

Precipitates This video is a demonstration of the colour of three metal hydroxide precipitates - copper(II) hydroxide, iron(II) hydroxide and iron(III) hydroxide.

Solutions containing copper(II) ions are typically blue in colour. When sodium hydroxide is added, copper(II) hydroxide forms as a blue precipitate. It decomposes to form copper(II) oxide when it is left to stand.

Solutions containing iron(II) ions are typically pale green in colour. When sodium hydroxide is added, copper(II) hydroxide forms as a dirty green precipitate. It is oxidised by the oxygen in air to form iron(III) hydroxide when it is left to stand.

Anion Test - Chloride Ions

Solutions containing chloride ions are typically colourless in colour.

To test for the presence of chloride ions in solution, you may use the silver nitrate test.

Thermal Decomposition of Copper(II) Sulfate Pentahydrate  Copper(II) sulfate pentahydrate takes the form of blue crystals.

Thermal Decomposition of Calcium Nitrate  A pure sample of hydrated calcium nitrate appears crystalline and glossy because of the water of crystallisation.

As you first gently heat the crystals, the water of crystallisation escapes as water vapour, condensing along the sides of the test-tube as water droplets. This forms a highly concentrated solution of calcium nitrate, which boils.

Upon further gentle heating, all of the water of crystallisation is eventually removed, leaving behind a powdery anhydrous form of calcium nitrate.

Switching to strong heating, the calcium nitrate soon melts and decomposes into calcium oxide, brown nitrogen dioxide gas and oxygen gas.

Thermal Decomposition of Zinc Carbonate  Zinc carbonate is a white powdery solid. When it is heated strongly, it starts to turn yellow and decompose - carbon dioxide gas is evolved, which forms a white precipitate in limewater.

IT Lesson 2 The video shows several students from Juying Secondary School performing laboratory procedures.

IT Lesson 1 The video is a demonstration of a set of procedures. Read the procedures as they appear in the video. Write down all of your observations for each step.