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TGW1:
What is an acid?
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Notes
on the video of ethanoic acid and calcium carbonate.
Students should notice the bubbles and should recognise these
as a sign that there is a chemical reaction, with a new substance
being formed which does not dissolve in water and is in the
gas state. In addition, after five hours there is only a small
amount of marble left. Students should be able to suggest
that other new substances may be dissolved in the water –
they know that calcium carbonate itself does not dissolve
in water.
Notes on the first video of hydrochloric acid and
magnesium, and related ‘Think for Yourself’ questions
Stop the video when the lighted splint is brought up to the
mouth of the test tube, then advance frame by frame to catch
the ignition of the hydrogen.
What tells you there is a chemical reaction?
The magnesium is used up. A new substance
is formed that is in the gas state. It does not dissolve in
water and bubbles out.
What is the new substance in the gas state? Explain.
Hydrogen. It sets alight. There are
hydrogen atoms in the hydrochloric acid that could make the
substance hydrogen.
Is this the only new substance?
No. There are magnesium and chlorine
atoms to account for: there must be at least one other new
substance.
Why can't you see any other new substances? Remember, hydrochloric
acid is a solution in water.
They must be dissolved in the water
and have no colour.
Why does the same thing happen to the second lump of magnesium?
The first lump of magnesium was not
enough to react with all of the hydrochloric acid.
Suppose you keep on adding more magnesium. When would you
know you had added enough to react with all of the hydrochloric
acid?
There would be no more fizzing. There
would be left over magnesium.
How could you find out what was dissolved in the water?
Take out the left over magnesium
and allow the water to evaporate.
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Science Enhancement Programme CD-ROM 2005 |
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user
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