The Chemical History of a Candle · Lecture IV, part 1 · Part 4: Lecture IV: Oxygen
10. Pulling water apart with electricity
Goal: Your child can explain how Faraday used a battery to split water into gas, and then turned the gas back into water.
You'll need
- Science notebook and colored pencils
What's in the book
Faraday shows what his battery can do: it pulls something brown out of a salt solution on paper (he writes the word "juvenile" with it), moves copper from one plate to the other, and turns water into a gas that explodes with a spark and becomes water again.
The lesson, step by step
Hook question
SayHydrogen comes out of water. If something else is in water too, how could we pull it out and see it?
Read together
Read pages 99 to 110, stopping at "Just now you saw that one end of this battery."
I see you are not tired of the candle yet, or I am sure you would not be interested in the subject in the way you are.
What Faraday did
Watch only: don't try this at home.
First he dissolved copper in nitric acid, making red fumes and a blue liquid. With the battery wires he pulled a brown substance out of a salt solution on wet paper, and wrote the word "juvenile" with it. He dipped two platinum plates in the blue liquid and the battery coated one plate with copper; when he swapped sides, the copper moved over.
Strong acids, toxic fumes and a large battery are laboratory work. If you want to see it, search online for a video of a chemistry teacher doing this demonstration and watch it together.
Water into gas, and back again
Faraday passed the battery's electricity through water with a little acid in it. It bubbled as if boiling, but the gas did not turn back into water when cool: it was a permanent gas. It burned with a bang. Then he put some in a strong closed glass vessel and set it off with an electric spark. The gas vanished, and drops of water ran down the inside.
The water of the candle had the atmosphere helping to produce it; but in this way it can be produced independently of the air.
Explosions in closed glass vessels are strictly for the laboratory.
The idea in plain words
SayThe battery split water into gas. The spark joined the gas back into water. So water must hold hydrogen and some second thing that a candle normally takes from the air.
Draw it
Have your child draw the story as a loop: water → (battery) → gas → (spark) → water. Label what Faraday did at each arrow.
Say it back and check
Narration prompts: How did Faraday test whether the bubbles were steam? What happened when he sparked the gas? How was this water different from the candle's water?
Check questions:
1. How did Faraday know the gas from the water was not steam?
2. What did the copper experiment show the battery could do?
3. What must water contain besides hydrogen?
Afterwards
Notice it this week: copper-colored coins, wires or pipes; Faraday moved copper from place to place with electricity, and the same idea is used to coat metal objects today.
Tip
Faraday calls the battery's flash a "telegram" from Mr. Anderson: a joke about the new telegraph of his day.
Answers to the book's problems
1. It stayed in the jar as a gas and did not condense into water, as steam would when cooled. 2. It could pull a substance out of a solution and move it from one plate to the other. 3. The substance that a candle takes from the air and joins to hydrogen to make water (named oxygen in the next lesson).
Worked out for this site from the scan. If a number in your copy differs, trust the book.