Chemical Tests Flashcards
(26 cards)
What is the method for carrying out a flame test?
- Clean a platinum wire loop by dipping it in dilute hydrochloric acid (HCl).
- Hold the loop in a Bunsen burner flame until it burns without any color (to remove impurities).
- Dip the clean loop into the sample you want to test.
- Place the loop back into the hottest part of the flame (the blue part).
- Observe the color of the flame to identify the metal ion present.
What flame color does lithium (Li⁺) produce in a flame test?
Red
What flame color indicates the presence of sodium ions (Na⁺)?
Yellow
What color flame does potassium (K⁺) give in a flame test?
Lilac
What flame color is shown by calcium ions (Ca²⁺)?
Orange-red
What flame color is produced by copper ions (Cu²⁺)?
Blue-green
How do you prepare the wire loop for a flame test?
Clean it by dipping in dilute hydrochloric acid and heating in the flame until no color appears.
What color precipitate forms when copper (II) ions react with sodium hydroxide?
Blue precipitate
What color precipitate forms when iron (II) ions react with sodium hydroxide?
Sludgy green precipitate.
What color precipitate forms with iron (III) ions and sodium hydroxide?
Reddish brown precipitate.
How do you test for ammonium ions (NH₄⁺)?
- Add sodium hydroxide to the solution
- If ammonia gas is produced (smelly and turns damp red litmus paper blue)
- Ammonium ions are present.
How do you test for carbonate ions (CO₃²⁻)?
- Add dilute hydrochloric acid
- If carbonate is present, carbon dioxide gas is released, which can be tested by bubbling through limewater to turn it cloudy.
How do you test for sulfate ions (SO₄²⁻)?
- Add dilute hydrochloric acid followed by barium chloride solution
- A white precipitate of barium sulfate means sulfate ions are present.
How do you test for halide ions (Cl⁻, Br⁻, I⁻)?
- Add dilute nitric acid followed by silver nitrate solution.
- Chloride gives a white precipitate (silver chloride).
- Bromide gives a cream precipitate (silver bromide).
- Iodide gives a yellow precipitate (silver iodide).
What colour precipitate does a chloride ion give?
White
What colour precipitate does a bromide ion give?
Cream
What colour precipitate does an iodide ion give?
Yellow
How do you test for chlorine gas?
- Chlorine bleaches damp blue litmus paper
- turning it white (may briefly turn red first).
How do you test for oxygen gas?
- Oxygen relights a glowing splint.
How do you test for carbon dioxide gas?
- Bubble the gas through limewater; it turns cloudy.
How do you test for hydrogen gas?
- Hydrogen makes a “squeaky pop” when lit with a lighted splint.
How do you test for ammonia gas?
- Ammonia turns damp red litmus paper blue and has a strong smell.
How can hydrated copper (II) sulfate crystals be used to test for water?
- Blue hydrated copper (II) sulfate turns white (anhydrous) when heated
- And turns back to blue when water is added.
What does “hydrated” and “anhydrous” mean?
Hydrated means containing water molecules; anhydrous means without water.
