These seven original questions cover the consumer and industrial chemistry lessons in SPM Chemistry. Write each answer on paper before opening the answer.
Practice questions
Question 1. Name the reactants and products when a fat reacts with sodium hydroxide to make soap.
Answer
Reactants: fat (or oil) and sodium hydroxide solution. Products: soap (the sodium salt of a fatty acid) and glycerol. The reaction is called saponification.
Question 2. Explain the role of the hydrophobic tail of a soap particle in removing grease.
Answer
The hydrophobic tail is a hydrocarbon chain that is attracted to grease, so it dissolves into the grease on the cloth. The hydrophilic head stays in the water, which lifts the grease off as droplets.
Question 3. A student washes a cloth with soap in hard water and sees scum and little lather. Explain these observations.
Answer
Hard water contains calcium and magnesium ions. These react with soap to form an insoluble scum, which uses up the soap, so little lather forms and less soap is available to clean.
Question 4. State the additive type that best solves each problem: (a) bread grows mould in three days, (b) cooking oil turns rancid, (c) a fruit jelly will not set firmly.
Answer
(a) Preservative, which slows the growth of microorganisms. (b) Antioxidant, which slows oxidation of the oil. (c) Stabiliser or thickener, such as gelatin, which gives a firmer texture.
Question 5. A fictional toothpaste claims to “remove stains faster”. Paste M took 30 s with a soft brush and paste N took 45 s with a hard brush. Can the claim be supported?
Answer
No. The brush type changed as well as the paste, so the difference in time cannot be blamed on the paste. A fair test would use the same brush for both pastes and change only the paste.
Question 6. Process J makes 10 kg of product with 4 kg of waste, and process K makes 10 kg with 1.5 kg. Using waste as the only criterion, which is greener?
Answer
Process K is greener on this criterion. It produces 4 − 1.5 = 2.5 kg less waste for every 10 kg of product.
Question 7. A label says a cleaner is “natural, so better for the environment”. Explain why this is not enough to conclude the cleaner is greener.
Answer
“Natural” describes where the ingredients come from, not how much waste, how hazardous a substance or how much energy the process uses. A conclusion needs measured evidence on the criteria used to judge green chemistry.
If you got these wrong
- Questions 1 to 3: interpreting soap and detergent chemistry.
- Question 4: explaining food additive functions.
- Questions 5 and 7: separating product claims from evidence.
- Question 6: discussing green chemistry with given criteria.
Log each miss in the mistake log and paper-error review, then retry with the timed practice session builder.
For a teacher to go through a full attempt with you, see online one-to-one Chemistry tuition.