C4.2 Flashcards
How do you test for carbon dioxide (CO₂) gas?
Bubble the gas through limewater (calcium hydroxide). If CO₂ is present, the limewater turns milky/cloudy.
How do you test for hydrogen (H₂) gas?
Hold a burning splint at the open end of a test tube. If hydrogen is present, it makes a ‘squeaky pop’ sound.
How do you test for chlorine (Cl₂) gas?
Place damp litmus paper into the gas. If chlorine is present, the paper is bleached white.
How do you test for oxygen (O₂) gas?
Insert a glowing splint into a test tube. If oxygen is present, the splint relights.
What is the flame test used for?
To identify metal ions by the color of the flame when heated.
What color does lithium (Li⁺) produce in a flame test?
Crimson red.
What color does sodium (Na⁺) produce in a flame test?
Yellow.
What color does potassium (K⁺) produce in a flame test?
Lilac.
What color does calcium (Ca²⁺) produce in a flame test?
Orange-red.
What color does copper (Cu²⁺) produce in a flame test?
Green.
How do you identify metal cations using sodium hydroxide (NaOH)?
Add NaOH to the solution and observe the precipitate color.
What color precipitate does calcium (Ca²⁺) form with NaOH?
White (no change in excess NaOH).
What color precipitate does copper (II) (Cu²⁺) form with NaOH?
Blue (no change in excess NaOH).
What color precipitate does iron (II) (Fe²⁺) form with NaOH?
Green (no change in excess NaOH).
How do you test for carbonates (CO₃²⁻)?
Add dilute acid — if carbon dioxide gas is produced (turns limewater cloudy), carbonates are present.
Example: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
What color precipitate does iron (III) (Fe³⁺) form with NaOH?
Orange-brown (no change in excess NaOH).
What color precipitate does zinc (Zn²⁺) form with NaOH?
White, but it redissolves in excess NaOH.
How do you test for halide ions (Cl⁻, Br⁻, I⁻)?
Add dilute nitric acid (HNO₃) to remove impurities.
Add silver nitrate (AgNO₃) solution.
Observe the color of the precipitate.
What color precipitate do different halide ions form with silver nitrate?
Chloride (Cl⁻): White
Bromide (Br⁻): Cream
Iodide (I⁻): Yellow
What are the advantages of instrumental methods for identifying substances?
More accurate
Highly sensitive
Rapid results
Why is nitric acid (HNO₃) used before testing for halides?
To remove carbonate ions, which could form a white precipitate and give a false positive.
How do you test for sulfate ions (SO₄²⁻)?
Add dilute hydrochloric acid (HCl) to remove impurities.
Add barium chloride (BaCl₂) solution.
White precipitate indicates sulfate ions.
Why is hydrochloric acid (HCl) used before testing for sulfates?
To remove carbonate ions, which could also form a white precipitate.
What is spectroscopy, and why is it useful?
Spectroscopy identifies elements by analysing light emissions, which is quick and precise.
How is flame emission spectroscopy different from a flame test?
Flame tests only show color (qualitative).
Flame emission spectroscopy provides a spectral pattern (quantitative and qualitative).
What information can be obtained from a flame emission spectroscopy chart?
The wavelength of light shows the element present.
The intensity of the wavelength shows the concentration of the element.
What is a reference set of data, and how is it used?
A set of known values used to compare unknown substances in instrumental analysis.
Why are instrumental methods preferred over traditional chemical tests in industry?
They are faster, more sensitive, and can detect very small amounts.
Useful in forensics, medicine, and environmental testing.
