Practice Test GeeksGCE O-Level Practice Test
← All O-LEVEL Flashcard Decks

Combined Science — Chemistry Flashcards

6 cards from real O-LEVEL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 Combined Science — Chemistry flashcards as text

  1. Which gas is produced when zinc reacts with dilute hydrochloric acid?

    Answer: Hydrogen

    Zn + 2HCl → ZnCl₂ + H₂. Hydrogen gas is produced, which burns with a squeaky pop when tested with a lighted splint.

  2. What is the formula for sulfuric acid?

    Answer: H₂SO₄

    Sulfuric acid has the formula H₂SO₄ — it contains two hydrogen atoms, one sulfur atom, and four oxygen atoms.

  3. What is the process of separating a mixture of liquids with different boiling points called?

    Answer: Fractional distillation

    Fractional distillation separates mixtures of liquids (like crude oil or air) based on their different boiling points.

  4. What is the oxidation state of oxygen in most compounds?

    Answer: -2

    Oxygen has an oxidation state of -2 in most compounds (exceptions include peroxides where it is -1, and OF₂ where it is +2).

  5. Which type of formula shows the simplest ratio of atoms in a compound?

    Answer: Empirical formula

    The empirical formula shows the simplest whole number ratio of atoms of each element in a compound.

  6. What colour is the precipitate formed when iron(III) ions react with sodium hydroxide?

    Answer: Rust/brown

    Iron(III) ions (Fe³⁺) form a rust-brown precipitate of iron(III) hydroxide (Fe(OH)₃) when NaOH is added.

How this page was made: written with AI tools and published by Nathan Beja, founder of Practice Test Geeks, who is responsible for its content. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

  1. file.go.gov.sg — Retake policy · verified Nov 2026
  2. seab.gov.sg — Passing score, score release, test delivery, eligibility, fees, registration · verified Nov 2026