Reaction #6 - Colour change

Hi all,

I have decided to share a colour changing experiment with you. If you have seen us doing experiments in class after PSLE, the experiment you have seen is this one.

For the benefit of those who haven't done so, I shall put it down here.

Step 1 - Dissolve copper sulfate and sodium chloride (more commonly known as table salt) in separate test tubes.

Step 2 - Add the copper sulfate solution to the sodium chloride solution, drop by drop. You will see the copper sulfate solution turning from blue to green! Why is that so?

The answer is simple - copper sulfate and sodium chloride react to form copper(II) chloride and sodium sulfate. Sodium sulfate is colourless while copper(II) chloride is green, making the solution green overall.

Copper sulfate + Sodium chloride → Copper(II) chloride + Sodium sulfate
CuSO₄ + 2 NaCl → CuCl₂ + Na₂SO₄

Hope you've enjoyed reading it!

Reaction by YOSF

Reaction #5 - How to make carbonic acid

Carbonic acid is a weak acid, but if you want to make it, here's how:

Materials:

• Vinegar / calcium chloride powder (vinegar - please follow normal steps and "A" steps, calcium chloride - please follow normal steps and "B" steps)
• Sodium bicarbonate
• Water
• 25ml graduating cylinder
• 1000ml (1 litre) beaker
• Conical flask with hole at the side that connects to a glass pipette
• Stopper

Step 1: Place the 25ml graduating cylinder into the 1000ml beaker.

Step 2: Pour the sodium bicarbonate into the conical flask.

Step 3: Pour water into the graduating cylinder.

Step 4: Put the glass pipette into the graduating cylinder.

Step 5A: Pour the vinegar (a bit will do) into the conical flask and stopper it off.

Step 5B: Add the calcium chloride into the conical flask and then add 10 ml of water (stopper it off immediately).

Step 6: Wait till no more gas bubbles come out of the pipette.

Step 7: Obtain the product (it's in the graduating cylinder)

Here're the chemical equations of this process:

For A:

Sodium bicarbonate + Vinegar (Acetic / ethanoic acid) → Sodium acetate / ethanoate + Water + Carbon dioxide

NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂

For B:

Sodium bicarbonate + Calcium chloride → Sodium chloride + Calcium carbonate + Water + Carbon dioxide

2NaHCO₃ + CaCl₂ → 2NaCl + CaCO₃ + H₂O + CO₂

(This actually goes in a multi-step process but I'm just simplifying it here.)

In both steps, the carbon dioxide dissolves into the water in the graduating cylinder to form carbonic acid:

Carbon dioxide + Water → Carbonic acid

CO₂ + H₂O → H₂CO₃

Improvements: Add crushed ice and water to the beaker containing the graduating cylinder (increases yield because gases dissolve better in colder water).

 

Good luck! 加油！

Reaction by GITS

Reaction #4 - How to make copper(II) sulfate

Copper(II) sulfate, also known simply as copper sulfate (chemical formula: CuSO₄), is the most commonly-used copper compound in laboratories. Due to the fact that it is commercially available (in fact, it is very widely available in many areas), it is not commonly prepared in laboratories.

That is why I am going to show you how to make copper sulfate here.

This is the more simple and straightforward way to make it:

Copper + Sulfuric acid → Copper sulfate + Sulfur dioxide + Water
Cu (s) + 2 H₂SO₄ (l) → CuSO₄ (aq) + SO₂ (g) + 2 H₂O (l)

If you don't have sulfuric acid available, you can use this method, although you will need to pass an electric current through it with 2 electrodes made of copper to carry out electrolysis:

Cu (s) + MgSO₄ (aq) + 2 H₂O → CuSO₄ (aq) + Mg(OH)₂ (s) + H₂ (g)

I hope you have enjoyed reading my postings!

Reaction by YOSF

Reaction #3 - Making sodium hydroxide

Sodium hydroxide is a well-known strong base (an alkali). It is corrosive (yes, not only acids are corrosive) and is commonly involved in chemical reactions.

Below are a few ways to make sodium hydroxide:

Sodium metal + Water → Sodium hydroxide + Hydrogen gas
2 Na (s) + 2 H₂O (l) → 2 NaOH (aq) + H₂ (g)

Sodium ethoxide + Water → Sodium hydroxide + Ethanol
NaC₂H₅O (s) + H₂O (l) → NaOH (aq) + C₂H₅OH (l)

Sodium metal + Lithium hydroxide → Sodium hydroxide + Lithium
Na + LiOH → NaOH + Li

These methods work quite well, but be careful: Sodium metal is highly reactive and will react violently and with so much heat that the hydrogen gas given off (during the first reaction) might ignite. In the second reaction, sodium ethoxide and water react violently. For the third reaction, the by-product, lithium metal will also, quickly and violently, react with excess water. So you might end up with a mixture of lithium hydroxide and sodium hydroxide.

Reaction by YOSF

Reaction #2 - Making manganese(II) carbonate

This is a demonstration of a precipitation reaction.

Manganese(II) sulfafte + Sodium carbonate →
Manganese(II) carbonate (precipitate) + Sodium sulfate
MnSO₄ (aq) + Na₂CO₃ (aq) → MnCO₃ (s) + Na₂SO₄ (aq)

Light pink manganese(II) carbonate precipitate is formed by this reaction.

Reaction by YOSF