Chemistry/Observing Chemical Changes Marking Scheme
Maximum = 9
(2) OBSERVATIONS:
- Copper(II) chloride is a blue-green solid.
- When placed in water, the crystals turn bright green with a slight blue tinge in the water above the crystals.
- When stirred, the crystals dissolve and form a light blue solution. The initial temperature is 22oC.
- The aluminum foil is a shiny silver-coloured metal.
- When the aluminum foil is placed in the solution
- — a red solid appears on the surface of the aluminum foil
- — bubbles of gas are produced
- — the temperature rises to over 50oC
- — the solution’s colour changes from blue to murky gray
- — the aluminum foil disintegrates and almost completely disappears
- The red material, when dried is crumbly and dark red
- When the red solid is ground in a mortar and pestle, the solid appears to be shiny red–brown, like copper metal.
DISCUSSION
1. What physical change(s) occurred during this experiment?
(1) The copper(II) chloride dissolved in water.
2. Make a list of the chemical changes you observed and the evidence you have to support each statement.
(2)
- A gas was produced because bubbles were seen.
- A new substance was formed as shown by the fact that a red solid was formed that was not present beforehand.
- A substance changed form as was seen by the fact that the aluminum foil disintegrated and disappeared.
- A starting substance disappeared because the blue colour in the solution disappeared.
3. Where do you think the aluminum foil went?
(1) The aluminum foil went into solution.
4. When copper is chemically reacted, the solid metal dissolves and forms a blue solution. What evidence do you have that dissolved copper is or is not left in solution at the end of your reaction?
(1) Dissolved copper was not present in solution at the end of the reaction because the blue colour had disappeared.
5. What do you think the red solid was? What evidence do you have to support this conclusion? (1) The red solid was copper because the colour of the dissolved copper disappeared from solution and the red solid had the appearance of copper when it was polished.
6. Is it possible that the bubbles were caused by boiling and not by a chemical change? Explain.
(1) The bubbles were not due to boiling because the temperature of the water was less than 100oC.
