Notice - Renaming of Chemistry Blog

 IMPORTANT NOTICE

On 4 Feb 2011, 1:08 pm GMT, the GITS & YOSF Company's Chemistry Theories blog has been changed to GITS and YOSF Company's Chemistry Blog.

The URL has also been changed from gyc-chemistrytheories.blogspot.com to gyc-chemistryblog.blogspot.com.

Reaction #8 - Aluminium with acid and alkali

Aluminium is amphoteric, which means it reacts with both acid and alkali to form other compounds.

Let's take this example:

Acid:
Aluminium + Nitric acid → Aluminium nitrate + Hydrogen
2 Al + 6 HNO₃ → 2 Al₂(NO₃)₃ + 3 H₂

Alkali:
Aluminium + Sodium hydroxide + Water → Sodium aluminate + Hydrogen
2 Al + 2 NaOH + 2 H₂O → 2 NaAlO₂ + 3 H₂

Hope you've enjoyed reading it!

Reaction #7 - Alka-Seltzer tablet

I'm sure all of you have heard about the effervescence of an Alka-Seltzer tablet (an antacid) when it is placed in water. But do you know how it works?

Well, here is the answer: The Alka-Seltzer tablet contains sodium bicarbonate (and a little bit of potassium bicarbonate) and anhydrous citric acid. In solid forms, the chemicals do not react. But once they are dissolved, they react vigorously:

C₆H₈O₇ (aq) + 3 NaHCO₃ (aq) → Na₃C₆H₅O₇ (aq) + 3 H₂O (l) + 3 CO₂ (g)
Citric acid + Sodium bicarbonate → Sodium citrate + Water + Carbon dioxide

Thus, the carbon dioxide gas bubbles out of the solution.

Reaction by YOSF

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