Acid Reactions & Salts

Activities to try

1. 1

   The salt maker: run reactions, name the salt, write the word equation

   Why it works: Neutralising or reacting an acid converts it into a real, recoverable salt (plus hydrogen or water) — matter is conserved and rearranged, not destroyed — and the salt's name follows predictably from the acid and the metal.

   1. Choose dilute hydrochloric or sulfuric acid and pair it with a moderately reactive metal such as magnesium, zinc or iron (not copper, which does not react, and never sodium or potassium); observe bubbles rising and test the gas at the mouth of the tube with a lit splint — a squeaky pop signals hydrogen. (Nitric acid is fine for the naming rule with alkalis and oxides, but with metals it usually gives nitrogen oxides rather than hydrogen, so it is not used for this run.)
   2. Keep the same acid but this time use an alkali (e.g. sodium hydroxide solution) instead of the metal; with indicator already in the acid, add the alkali gradually, a little at a time — observe that there is no fizz, and watch the indicator change until it shows pH 7 (neutralisation), giving salt + water.
   3. After each run, state the salt's full name before it is written out, deriving the surname from the acid (chloride/sulfate/nitrate) and the first word from the metal or the metal in the alkali, then write the complete word equation (e.g. magnesium + hydrochloric acid → magnesium chloride + hydrogen).
   4. Finish by evaporating the neutral solution to drive off the water and leave visible salt crystals in the dish (for purer crystals, repeat the neutralisation with the same volumes but no indicator, because indicator left in the solution colours the salt).
   5. Repeat with new pairings — acid/reactive metal (dilute hydrochloric or sulfuric acid), acid/alkali, and acid/metal oxide or hydroxide (e.g. copper oxide + sulfuric acid → copper sulfate + water) — so the naming rule generalises across examples rather than being memorised as a list.
2. 2

   Predict–observe–explain: what is left when the water evaporates?

   Why it works: A 'cancelled to nothing' model predicts an empty dish; the solid salt crystals that remain disprove it. Neutralisation produces a salt plus water, and mass is conserved as atoms rearrange into new products.

   1. Neutralise an acid with an alkali until the indicator reads pH 7.
   2. BEFORE evaporating, write down a prediction: if all the water is driven off, what (if anything) will remain, and WHY?
   3. Evaporate the water and compare the result with the prediction.
   4. Write the word equation for what happened (acid + alkali → salt + water) and explain in words why 'neutral' does not mean 'empty'.
3. 3

   Complete and name: word-equation practice across families

   Why it works: The productive salt-naming rule and the family distinction (hydrogen vs water) can be applied to new pairings, not just recognised in familiar ones.

   1. Complete partial word equations, e.g. 'sulfuric acid + zinc → zinc ____ + ____', filling both the salt surname and the gas.
   2. Match each acid to its salt ending: hydrochloric→chloride, sulfuric→sulfate, nitric→nitrate.
   3. Decide, for a given pairing, whether hydrogen or water is produced, and justify the choice by naming the family (acid+reactive metal vs acid+alkali or acid+metal oxide/hydroxide).
   4. Name the salt from an unfamiliar acid/base pair (e.g. hydrochloric acid + potassium hydroxide → potassium chloride + water) and state why it is not sodium chloride.
   5. State the pH at the neutralisation endpoint (7) and name the gas test for hydrogen (lit splint, squeaky pop).