Open Question: I want an experiment that requires downward displacement of water by H2 gas (ie metal+acid-->salt+hydrogen)...?

Some questions:
I want to measure the rate of H2 produced, so I need a metal and acid that react together well, but not too quickly or else I won't have time to record how much H2 is being produced. What metals could I use?

Also

Will this work? Can I collect H2 gas by downward displacement of water?

Thanks

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