Lab session 6

Part 2

The properties of acids

ACTIVITY 1

1. Place a piece of blue litmus paper, red litmus paper and universal indicator on a white tile. 

2. Use the dropper to carefully add a drop of dilute sulfuric acid to all three strips of indicator. 

Results: 

-Blue litmus paper turns red

-Red litmus paper turns red

-Universal indicator turns red (pH 4.0): 

Conclusion: Acids turn Blue litmus paper red and Red litmus paper red. Acids change the color of the universal indicator. The pH range of acids is <7. 

ACTIVITY 2

1. Using a clean test tube, add dilute hydrochloric acid to the test tube up to 2cm in height. 

2. Light the Bunsen burner.

3. Carefully slip one piece of magnesium ribbon into the test tube. 

Observations: The magnesium ribbon dissolves and the test tube feels hot to the touch.

4. Using a wooden splint, light it using the Bunsen flame and place it at the mouth of the test tube. 

Observations: When the wooden splint was placed in the test tube, a "pop" sound was produced. 

ACTIVITY 3

1. Using a clean boiling tube, add dilute hydrochloric acid to the test tube up to 2cm in height. 

2. Pour calcium carbonate into another test tube up to 2cm in height. 

2. Prepare a set up according to the diagram:

3. Add a spatula of sodium carbonate to the acid in he boiling tube. 

4. Fix the rubber stopper of the delivery tube on the mouth of the boiling tube and place the other end into the test tube containing calcium carbonate.

Observations: A white precipitate is formed and the calcium carbonate (limewater) turns cloudy. 

Lab session 6

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)

Lab session 5

In this lab session, we explored various changes, namely CHEMICAL and PHYSICAL changes in elements through heating.

What is the difference between Chemical Change and Physical Change?

Chemical Change:
-There is a change in energy (Energy is absorbed of given off)
-A new substance is formed (Chemical properties are changed) 
-The process is irreversible (The element(s) used cannot be separated)

E.g. forming of compounds

Physical Change
-There is no change in energy (No energy is absorbed or given off)
-No new substance is formed (Chemical properties stay the same)
-The process is reversible (The element (s) used can be separated by physical means)

E.g. Melting, boiling, sublimation, etc. 

Activity: Heating and Cooling Solids

Materials used
-Sodium Chloride (White solid; crystal form)
-Copper (II) Carbonate (Green solid; powder form)
-Magnesium (Silvery metallic strip, solid form)

Procedures

For Sodium Chloride and Copper (II) Carbonate:
-Gently heat a spatula of the solid in a dry test tube
-If there is no observable change, heat strongly by placing the bottom of the test tube at the hottest part of the flame

For Magnesium:
-Hold the strip of magnesium ribbon using a pair of metal tongs and heat it directly using a Bunsen flame
-DO NOT stare directly at the flame.

Copper (II) Carbonate:
Before heating: Green solid in powder form
During heating: White fumes coming out and black solid formed.
After cooling: No visible change.
Type of change: Chemical change.

Before:                                                                                                  After:

Word equation: Copper (II) Carbonate -------------------------------> Copper (II) oxide + Carbon dioxide
                                                             (Thermal decomposition)


Sodium Chloride:
(Didn't manage to get any pics. :/)
Before: white solid in crystal form.
During heating: Melted into a clear liquid (molten Sodium Chloride)
After cooling: Solidified to form back a white solid.
Type of Change: Physical Change.



Magnesium:
(Didn't manage to get the pics of the reaction cause we were too busy freaking out. :p But it was super cool. :))

Before heating: Silvery metallic strip

During heating: It burned with a bright light (REALLY bright)

After cooling: White powdery solid (Ash) 

Type of Change: Chemical change.

Before:          
                                                                                                               After:

Word equation: Magnesium + oxygen ------------------> Magnesium Oxide
                                                             (Combustion)