Wild Chemistry Ride 10:


Kinetic Particle Theory Practical!

Activity 1: Chemical changes due to light

We first did a practical to observe what will happen to sections of a filter paper when exposed/ not exposed to light.

The procedure is as follows:
We placed a piece of filter paper on a petri dish and soaked it with sodium chloride solution, then placed it on a clean white tile. After dripping some silver nitrate all over the filter paper, we observed some white precipitate covering the filter paper. We quickly placed the opaque object on top of the filter paper, and placed the paper in bright light for about 20 minutes.

This is what we observed after  20 minutes: 

As shown, the area of the filter paper which the opaque object covered (or the area not exposed to light) was still white. On the other hand, the area of the filter paper which was not covered by the opaque object (or the area exposed to light) had a purple-greyish colour. 

Also, earlier when the silver nitrate was dripped onto the filter paper soaked with sodium chloride, a chemical change occurred. It was identified to be a chemical change as silver nitrate and sodium chloride, two colourless substances, react rapidly to form a new substance, a white precipitate.

Activity 2: Combination, decomposition and combustion reactions

Combination--> Two reactants combine to yield one or more products
Decomposition--> One reactant is broken down into two or more products
Combustion--> Occurs when a substance (usually a compound) reacts with oxygen, and releases energy 

We conducted a few more short experiments:


1. For magesium: My benchmate held a strip of magnesium ribbon using a pair of metal tongs and heated it directly at the hottest part of a Bunsen flame.
Observations: The silver metallic strip burned and produced a very bright flame and light. After that, there was white powder on the strip. It was a combination type of reaction.

2. For the reaction between potassium iodide solution and lead nitrate solution: 
a) We filled a boiling tube with potassium iodide to about 1cm, then added 5 drops of lead nitrate solution to the boiling tube. 
Observations: The two colourless liquids, when added together, became a yellow mixture. 



b) After achieving the yellow mixture, we added water to the boiling tube until it is half-full and heated it to obtain a near colourless solution. Then, we allowed the tube to cool for about 10 minutes.
Observations: When the diluted mixture was heated, there was effervescence and there were white fumes. Also, there were fewer yellow crystals over time, such that in the ned, a colourless liquid with few bright yellow crystals remained. 


One very interesting experiment was the teacher demonstration of propane gas. First, in a beaker of soap water, our teacher bubbled gas from the gas tap into the soap water. Next, one of our classmates volunteered to wet her hand and scooped up a handful of bubbles. When our teacher light a lighter at the bubbles, my whole class was very amazed to see that it caused a big flame when the splint lighted the bubbles. It was a combustion type of reaction. Also, to our surprise, our classmate's hand was not burnt and she did not feel any pain either. 

The experiments were great and I can't wait to explore more on Chemistry!

Click here to watch a video on propane gas lighting up!
Click here for another article and video on lighting of propane gas!