Cobalt and Copper Color Changes

This lesson covers two main tests for detecting the presence of water: using anhydrous copper(II) sulfate and cobalt(II) chloride paper. Anhydrous copper(II) sulfate turns from off-white to bright blue when hydrated, while cobalt(II) chloride paper changes from light blue to pink. The lesson also explores the historical use of cobalt(II) chloride as invisible ink, which becomes visible when heated. The video concludes with a summary of the color changes observed in these tests.

What is the primary purpose of the tests discussed in the lesson?

• To determine the pH level of water

• To measure the temperature of water

• To detect the presence of water

• To confirm the purity of water

What color does anhydrous copper(II) sulfate turn when it becomes hydrated?

• Bright blue

• Off-white

• Light pink

• Dark green

What does the term 'anhydrous' mean?

• Without salt

• With salt

• Without water

• With water

What color change occurs in cobalt(II) chloride paper when it detects water?

• Pink to light blue

• Bright blue to off-white

• Light blue to pink

• Off-white to bright blue

What is the anhydrous form of cobalt(II) chloride?

• Off-white

• Light blue

• Bright blue

• Pink

How can cobalt(II) chloride be used as invisible ink?

• By mixing it with lemon juice

• By using a dilute solution that turns blue when heated

• By writing with a concentrated solution

• By applying it on a hot surface

What happens to cobalt(II) chloride when it is heated?

• It becomes invisible

• It turns pink

• It turns blue

• It evaporates

Which of the following is a correct summary of the color changes observed in the tests?

• Copper(II) sulfate: off-white to pink; Cobalt(II) chloride: light blue to bright blue

• Copper(II) sulfate: pink to light blue; Cobalt(II) chloride: bright blue to off-white

• Copper(II) sulfate: off-white to bright blue; Cobalt(II) chloride: light blue to pink

• Copper(II) sulfate: bright blue to off-white; Cobalt(II) chloride: pink to light blue

What is the hydrated form of copper(II) sulfate?

• Pink

• Off-white

• Light blue

• Bright blue