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Introduction

An acid is a substance that produces H​​+ ions in water. These hydrogen ions react with other substances in definite ways, no matter which acid produced the hydrogen ions. This means that it if we know how one acid reacts with a substance, we can predict how any acid will react with that substance.

Task 1: Reactions of acids


A simulation to investigate the general reaction of acids

  1. Open Yenka file Model 1.
  2. The beaker on the balance contains dilute hydrochloric acid in water. Select the beaker and use the atom viewer to observe the contents. Describe what you see.
    Answer
    Hydrogen ions and chloride ions freely moving in water
  3. Add the sample of magnesium to the acid, and select the beaker to view the reaction in the atom viewer. You should be able to see the magnesium reacting with the hydrogen ions, releasing hydrogen and magnesium ions. If you look at the graph showing the mass of the contents of the beaker, you should see it decreasing. Why do you think the mass of the contents of the beaker is decreasing?
    Answer
    Because a gas (hydrogen) is being lost from the container.
  4. Copy down the word equation for the reaction occurring. You should see it in the reaction details.
    Answer
    Magnesium + hydrochloric acid → hydrogen + magnesium chloride
  5. The magnesium compound formed is called a salt. Hydrochloric acid produces chloride salts, while sulfuric acid forms sulfates and nitric acid forms nitrates. Suggest the name of the salt formed when sulfuric acid reacts with zinc.
    Answer
    Zinc sulfate
  6. All reactive metals will react with acids to form a salt and hydrogen. Copper is not reactive enough to do so. Try simulating the reaction of a sample of sodium in some acid. Why is this reaction never carried out?
    Answer
    Too dangerous
  7. Reload the simulation by pressing F5. Add the sample of magnesium carbonate to the acid. What happens?
    Answer
    Bubbles, and mass of contents decreases.
  8. The reaction occurring is:
    hydrochloric acid + magnesium carbonate → magnesium chloride + carbon dioxide + water
    The salt magnesium chloride is again formed in this reaction. Suggest why the mass decreases.
    Answer
    Carbon dioxide given off.
  9. This reaction occurs when any carbonate reacts with any acid. The only difference is that different acids produce different salts. Write the equation for the reaction between sodium carbonate and nitric acid. Test your idea by performing the simulation.
    Answer
    Sodium carbonate + nitric acid → sodium nitrate + carbon dioxide + water
  10. Reload the simulation again, and click on the graph. Change the x-axis scale so that the maximum mass is 105 g. Select the sodium hydroxide solution, and observe the atom viewer. You should see sodium ions and hydroxide ions in random motion. The hydroxide ions make the solution alkaline. What is the pH of an alkaline solution? 
    Answer
    More than 7, up to 14
  11. Now pour the sodium hydroxide solution into the beaker of acid. Quickly select the beaker on the balance and observe the atom viewer. What do you see?
    Answer
    Hydroxide ions and hydrogen ions colliding and reacting to form water, as well as sodium ions and chloride ions in motion
  12. At the end of the reaction, what was left in the beaker?
    Answer
    Water, sodium ions and chloride ions
  13. What happened to the mass of the beaker contents as the reaction occurred, and suggest a reason for the different behaviour in this case.
    Answer
    The mass doesn't change as the reaction takes place, because no gases are produced.
  14. Add some Universal Indicator to the solution formed, record the colour and use the appropriate colour chart to estimate the pH of the solution.
    Answer
    Green, pH = 7
  15. What sort of reaction has occurred?
    Answer
    A neutralisation reaction
  16. Sodium hydroxide solution is an alkali, and all alkalis react with acids to form a salt and water. What is the name of the salt formed in this reaction?
    Answer
    Sodium chloride
  17. Write a word equation for the reaction of sulfuric acid with potassium hydroxide solution. Test your ideas by simulating the reaction.
    Answer
    sulfuric acid + potassium hydroxide → potassium sulfate + water

Summary

All acids undergo the same reaction with metals forming a salt and hydrogen. They all react with carbonates forming a salt and water and carbon dioxide. They all neutralise alkalis producing a salt and water. Using this knowledge it is possible to predict the reaction of any acid with these types of compound.

Teacher Summary

  • This activity discusses acids and alkalis in terms of hydrogen and hydroxide ions, and may be suitable for more advanced pupils.