3.1.4 - Qualitative Analysis Flashcards
What is qualitative analysis in chemistry?
Qualitative analysis is the process of identifying the chemical components or ions present in a sample.
What is the purpose of flame tests in qualitative analysis?
Flame tests are used to identify metal ions based on the characteristic color they emit when heated in a flame.
What color flame does lithium produce in a flame test?
Lithium produces a crimson red flame.
What color flame does sodium produce in a flame test?
Sodium produces a bright yellow flame.
What color flame does potassium produce in a flame test?
Potassium produces a lilac flame.
What color flame does calcium produce in a flame test?
Calcium produces a brick red flame.
What color flame does barium produce in a flame test?
Barium produces a green flame.
What is the principle behind the precipitation reaction for qualitative analysis?
A precipitation reaction involves mixing two solutions to form an insoluble compound (precipitate), which can help identify ions present in a sample.
How do you test for the presence of carbonate ions (CO₃²⁻)?
To test for carbonate ions, add a dilute acid (e.g., hydrochloric acid) to the sample. If carbonate ions are present, carbon dioxide (CO₂) gas will be released, which can be tested using limewater (which will turn cloudy).
How do you test for the presence of sulfate ions (SO₄²⁻)?
To test for sulfate ions, add barium chloride (BaCl₂) solution to the sample. A white precipitate of barium sulfate (BaSO₄) will form if sulfate ions are present.
How do you test for the presence of chloride ions (Cl⁻)?
To test for chloride ions, add silver nitrate (AgNO₃) solution to the sample. A white precipitate of silver chloride (AgCl) will form if chloride ions are present.
How do you test for the presence of bromide ions (Br⁻)?
To test for bromide ions, add silver nitrate (AgNO₃) solution to the sample. A cream precipitate of silver bromide (AgBr) will form if bromide ions are present.
How do you test for the presence of iodide ions (I⁻)?
To test for iodide ions, add silver nitrate (AgNO₃) solution to the sample. A yellow precipitate of silver iodide (AgI) will form if iodide ions are present.
What is the test for ammonium ions (NH₄⁺)?
To test for ammonium ions, add sodium hydroxide (NaOH) solution to the sample and warm it. If ammonium ions are present, ammonia gas (NH₃) will be released, which has a characteristic pungent smell and can turn damp red litmus paper blue.
What is the test for the presence of nitrate ions (NO₃⁻)?
To test for nitrate ions, add iron(II) sulfate (FeSO₄) solution to the sample, then carefully add concentrated sulfuric acid (H₂SO₄) down the side of the test tube. A brown ring at the interface indicates the presence of nitrate ions.
How do you test for the presence of hydroxide ions (OH⁻)?
To test for hydroxide ions, use red litmus paper. If hydroxide ions are present, the litmus paper will turn blue.
How do you test for the presence of halide ions (Cl⁻, Br⁻, I⁻) in an aqueous solution?
Add silver nitrate (AgNO₃) solution, and observe the color of the precipitate formed:
- Chloride (Cl⁻) forms a white precipitate of silver chloride (AgCl).
- Bromide (Br⁻) forms a cream precipitate of silver bromide (AgBr).
- Iodide (I⁻) forms a yellow precipitate of silver iodide (AgI).
What is the test for sulfite ions (SO₃²⁻)?
To test for sulfite ions, add acidified potassium dichromate (K₂Cr₂O₇) solution. A positive test results in a color change from orange to green as the dichromate ion is reduced to the chromium(III) ion.
What is the test for flame tests to identify metal ions?
A flame test involves placing a sample of the metal compound on a wire loop and holding it in a flame. Each metal produces a characteristic flame color that can be used to identify the metal ion present.
How do you test for the presence of alkali metals (Group 1) using flame tests?
Alkali metals (Group 1) produce distinctive flame colors in flame tests:
- Lithium (Li): Crimson red
- Sodium (Na): Bright yellow
- Potassium (K): Lilac
- Rubidium (Rb): Red-violet
- Cesium (Cs): Blue-violet
How can you test for the presence of carbon dioxide (CO₂) gas?
To test for carbon dioxide (CO₂), bubble the gas through limewater. If CO₂ is present, the limewater will turn cloudy due to the formation of calcium carbonate (CaCO₃).
What is the test for the presence of oxygen (O₂) gas?
To test for oxygen (O₂), insert a glowing splint into the gas. If oxygen is present, the splint will ignite and burn more brightly.
What is the test for the presence of hydrogen (H₂) gas?
To test for hydrogen (H₂), apply a lit splint to the gas. If hydrogen is present, it will produce a popping sound.
What is the test for chlorine (Cl₂) gas?
To test for chlorine (Cl₂), use damp litmus paper. Chlorine will turn the paper bleached and can also cause it to turn from blue to white.
What is the role of reagents in qualitative analysis?
Reagents in qualitative analysis are used to trigger specific chemical reactions that help identify the presence of particular ions or compounds based on observable changes (such as color, precipitation, or gas evolution).
