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!

Wild Chemistry Ride 9:


Kinetic Particle Theory Group Assignment

For this group assignment, we had to match the substances to their particle models. 

Pictures of Substances:

Pictures of Particle Models:



We not only had to match the substances to their particle models, but we also had to explain each choice. As such, my group used properties of particulate models of the three states of matter for our explanation. Here is a table of such properties:

Last but not least... 
 Click here to view our responses to this assignment!

Wild Chemistry Ride 8:


Chromatography 

Did you know?: Chromatography was originated by a Russian botanist in 1906 who named this technique chromatography because he separated components of plant pigments into bands of colour for his experiment!

And here's a fun fact: Scientists use chromatography columns to purify substances from multiple chemical compounds and that narrow glass tube can measure up to 50mm and can be up to 1 meter tall!

Well for the experiment we did, it was on paper chromatography, where we separated the ink dyes of a ZIG marker pen. I managed to separate the ink of my marker pen into 3 components: yellow dye, pink dye and blue dye. The results were mostly similar to my classmates', however not all markers use the same constituent elements/ compounds thus there might be some difference in the component results.

Apart from the concept on paper chromatography, I also learnt that the Rf value is the (distance travelled by spot) ÷  (distance travelled by component), thus the value would always be less than 1. Also, I discovered how to measure the distance of the spot, which is the center of the area covered by the dye if the "spot" covers a large area.

I've also learnt that factors affecting the Rf value are 1. The type of solvent used, 2. The temperature of the solvent and 3. The type of paper used.

Wild Chemistry Ride 7:


Crystallisation

Crystallisation is based on the principle of variable solubilities of solutes in solvents at different temperatures, and it is the most common method used to purify soluble solids.

We did a practical where we attempted to purify copper (II) sulfate crystals. In summary, the solution of copper (II) sulfate dissolved in water is heated to form a hot, saturated solution. This heating allows for excess solvent to be removed via evaporation. As the hot saturated solution cooled, the dissolved solids appeared as crystals as the solubility of the solute decreases with decreasing temperatures. This means that as the temperature of the solution drops, less solute can be dissolved in the solution. The excess solute would then appear in the solution in the form of crystals. 

At first, I was confused as to why we had to stop heating the solution before all the solvent evaporated. However, later on I realised that leaving some solvent behind prevents decomposing of copper (II) sulfate into copper (II) oxide. Another reason was that soluble impurities will be left behind if all the solvent evaporated, because some solvent is required to keep teh soluble impurities dissolved, so taht it can be separated from the crystals by filtration. 

From this experiment, I not only learnt how to crystallise using the seeding method, but I also learnt that by controlling the variables such as the evaporation rate, the size and shape of the crystals can be controlled. For example, crystals obtained by rapid cooling are small, many in number and have ill-defined shapes. On the other hand, crystals obtained by slow cooling are large, small in number and have a more refined shape, like the shape of a snowflake.