A buried iron pipe corrodes. An average current of 28 mA leaves it for a whole year of 365 days…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A buried iron pipe corrodes. An average current of leaves it for a whole year of days. Each iron atom gives 2 electrons. Use and . How much iron is lost? How much zinc would a sacrificial block lose to give the same current?
Need a reminder? The key ideaShow
One ampere-hour is . A lead atom gives 2 electrons in the lead storage battery, a zinc atom gives 2 in the dry cell and an iron atom gives 2 when it rusts. Energy is . A fuel cell converts the energy of directly into electricity. Zinc, with a lower potential than iron, protects it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Charge. .
Step 2. Electrons. .
Step 3. Iron. .
Step 4. Zinc. .
Answer: of iron, or of zinc in a sacrificial block.
Check. A small current wears away a noticeable mass in a year. The zinc block is heavier than the iron it replaces, because zinc atoms are heavier and give the same 2 electrons.
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