C8- Chemical Analysis

• How do you test for chlorine gas?

  • Hold damp blue litmus paper near the gas.
  • Result: Litmus paper turns white (it gets bleached).
• How do you test for carbon dioxide?

  • Bubble the gas through limewater.
  • Result: Limewater turns cloudy/milky.
• How do you test for hydrogen gas?

  • Hold a lit splint near the gas.
  • Result: You hear a squeaky pop sound.
• How do you test for oxygen gas?

  • Insert a glowing splint into the gas.
  • Result: The splint relights.
• How do you test for carbonate ions (CO₃²⁻)?

  • Add dilute acid (like hydrochloric acid).
  • Result: Bubbles of carbon dioxide gas are produced (test with limewater, which turns cloudy).
• How do you test for sulfate ions (SO₄²⁻)?

  • Add dilute hydrochloric acid (HCl) and then barium chloride solution (BaCl₂).
  • Result: A white precipitate of barium sulfate forms.
• How do you test for halide ions (Cl⁻, Br⁻, I⁻)?

  • Add dilute nitric acid (HNO₃) and then silver nitrate solution (AgNO₃).Results:
  • Chloride (Cl⁻) → white precipitate
  • Bromide (Br⁻) → cream precipitate
  • Iodide (I⁻) → yellow precipitate
• How do you test for lithium ions (Li⁺)?

  • Flame test – red flame.
• How do you test for sodium ions (Na⁺)?

  • flame test – yellow flame.
• How do you test for potassium ions (K⁺)?

  • Flame test – lilac flame.
• How do you test for calcium ions (Ca²⁺)?

  • Flame test – orange-red flame.
• How do you test for copper(II) ions (Cu²⁺)?

  • Flame test – green flame.
• What is the test for metal ions/cations using sodium hydroxide (NaOH)?

  • Add NaOH solution to the metal ion solution and observe the colour of the precipitate formed.
• What colour precipitate does copper(II) (Cu²⁺) form with NaOH?

  Blue precipitate
• What colour precipitate does calcium (Ca²⁺) form with NaOH?

  White precipitate
• What colour precipitate does iron(II) (Fe²⁺) form with NaOH?

  Green precipitate
• What colour precipitate does iron(III) (Fe³⁺) form with NaOH?

  Brown precipitate
• What colour precipitate does magnesium (Mg²⁺) form with NaOH?

  White precipitate
• What happens when aluminium (Al³⁺) reacts with NaOH?

  • White precipitate forms at first.
  • With excess NaOH, the precipitate redissolves to form a colourless solution.Equation:Al³⁺(aq) + 3OH⁻(aq) → Al(OH)₃(s)
• What is a cation?

  A positively charged ion.
• What is an anion?

  A negatively charged ion.
• What is Flame Emission Spectroscopy (FES)?

  • analytical method used to identify metal ions in a solution by heating them in a flame and analysing the light emitted
• How does Flame Emission Spectroscopy work?

  1. The sample is placed in a flame.
  2. Metal ions become excited and release energy as light.
  3. A spectroscope detects the light and produces a line spectrum.
• What does the line spectrum in FES tell us?

  • The position of the lines tells us which metal ion is present (each ion has a unique pattern).
  • The intensity of the lines shows how much of the metal ion is present (the concentration).
• What are the advantages of Flame Emission Spectroscopy?

  • Very accurate
  • Very sensitive (detects small amounts)
  • Very fast (good for industrial use)
• Why is FES better than flame tests?

  • Can identify mixtures of metal ions.
  • Gives both qualitative (which ions) and quantitative (how much) data.
  • More precise and reliable than just looking at flame colours.