Part 1
Chemical Changes due to light
Procedure:
1. Select a clean, opaque object to be used for this experiment.
2. Place a piece of filter paper on a petri dish. Soak the filter paper with sodium chloride solution:
3. Remove the filter paper and place it on a clean white tile.
4. Carefully drip silver nitrate solution on the paper.
You will observe white precipitate (Silver chloride) being formed on the filter paper:
(Silver chloride + Sodium nitrate)
5. Place the opaque object on top of the filter paper. (We did not have time to do it with the opaque object, so we just did without it.)
6. Place the paper in bright light for 15-20 minutes
Results: Where the white precipitate formed, there was a purple colored patch. This is decomposed silver. The silver chloride formed in in the white precipitate decomposed under light to form silver metal.
Thermal decomposition
Procedure:
1. Add a level spatula of the copper (II) nitrate solid in a test tube
2. Gently heat the solid in the test tube over a Bunsen flame:
Here's multiple pictures to show the change over time:
Results: As can be observed, the copper (II) nitrate became darker, decomposing to form a black solid copper (II) oxide. Although it cannot be seen from the pictures above, effervescence was observed during the experiment, where oxygen and nitrogen dioxide were formed.
Copper (II) nitrate (s) --> Copper (II) oxide (s) + Oxygen (g) + Nitrogen dioxide (g)
Precipitation
1. Add 10cm^3 of aqueous copper (II) nitrate into a test tube.
2. Add 4 drops of aqueous sodium hydroxide into the test tube.
A blue precipitate is observed:
Results: A blue precipitate (Copper (II) hydroxide + sodium nitrate) is formed and remains after the reaction.
Copper (II) nitrate (l) + odium hydroxide (l) --> Copper (II) hydroxide + sodium nitrate
1. Fill a boiling tube with potassium iodide solution to about 1cm in height.
2. Add 5 drops of lead (II) nitrate solution to the boiling tube.
A yellow precipitate is formed:
(Potassium nitrate + lead (II) iodide)
3. Add water to the boiling tube until it is half full.
4. Heat the resulting mixture to obtain a near colorless solution.
5. Allow boiling tube to cool on a test tube rack for approximately 10 minutes.
Results: The yellow precipitate dissolved to form a colorless solution during heating and yellow crystals were formed upon cooling.
Potassium iodide (l) + lead (II) nitrate (l) --> Potassium nitrate + lead (II) iodide
Combustion
1. In a beaker of soap water, bubble gas (propane gas) from the gas tap into the soap water.
2. Light a lighter at the bubbles.
Results: Flames are observed. The water and colorless gas remains.
Propane (g) --> oxygen (g) + water (l)
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