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TGW1: What is an acid?
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.

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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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tgw1: acid
tgw2: notes
tgw3: questions
tgw4: notes
tgw5: notes
tgw6: nitric acid
tgw7: notes

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