Question

what do these two changes have in common?
using a large magnet to remove pieces of iron from a junkyard
a puddle freezing into ice on a cold night
select all that apply.
both are caused by cooling.
both are chemical changes.
both conserve mass.
both are changes of state.

Explanation:

1. Analyze "using a large magnet to remove pieces of iron from a junkyard": This is a physical separation (magnetic separation), no cooling involved, not a chemical change, not a change of state, but mass is conserved (mass of iron and other materials remains, just separated).
2. Analyze "a puddle freezing into ice on a cold night": This is a physical change (change of state from liquid to solid), caused by cooling, mass is conserved (mass of water remains as it freezes), not a chemical change.
3. Evaluate each option:

• "Both are caused by cooling": Magnet separation isn't caused by cooling, so this is incorrect.
• "Both are chemical changes": Neither is a chemical change (magnet separation is physical, freezing is physical), so this is incorrect.
• "Both conserve mass": In any physical or chemical change, mass is conserved (Law of Conservation of Mass). So this is correct.
• "Both are changes of state": Magnet separation isn't a change of state, so this is incorrect.

Answer:

Both conserve mass.