Year 10 Science · Unit 2 · Lesson 2
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Learning Goals
Compare two
Complete the table to compare a strong acid, a weak acid, and a strong base.
| Feature | Strong acid (e.g. HCl) | Weak acid (e.g. acetic acid) | Strong base (e.g. NaOH) |
|---|---|---|---|
| Typical pH range | |||
| Common example / name | |||
| One industrial or household use in Australia | |||
| Hazard level (low / moderate / high) | |||
| Ion released in excess in water |
Real-world context
Your stomach produces hydrochloric acid (HCl) at a pH of approximately 1.5 to help digest food. When you eat on an empty stomach and then take aspirin (acetylsalicylic acid, a weak acid), doctors warn that irritation and ulcers are more likely. Antacid tablets containing calcium carbonate (CaCO₃) or magnesium hydroxide (Mg(OH)₂) are commonly used across Australia to relieve acid-related discomfort.
(a) Explain why hydrochloric acid at pH 1.5 is essential for digestion. In your answer, refer to the role of H⁺ ions and why a very low pH is needed.
(b) Explain how an antacid tablet neutralises excess stomach acid. Name the type of reaction that occurs, describe what happens to the H⁺ ions from HCl, and name the products formed.
(c) Aspirin is a weak acid. Why might taking aspirin on an empty stomach (already very acidic at pH 1.5) cause more stomach damage than taking it with food (which raises the stomach pH to ~3)?
1. Car batteries use sulfuric acid (H₂SO₄). State whether this is a strong or weak acid, give its approximate pH, and explain one safety precaution someone should take when handling it.
2. Phenolphthalein indicator is colourless in acid and turns pink in base. A student adds phenolphthalein to an unknown solution and it stays colourless. What can the student conclude about the pH of the solution? Explain why this conclusion cannot tell the student exactly what the pH is.
Wrap Up
In one sentence, what was the main idea of this lesson?