Analytical Chem Flashcards
How can you test if a substance is pure?
By measuring its melting or boiling point. A pure substance will have a sharp, specific melting/boiling point, while a mixture melts/boils over a range of temperatures.
What color flame does lithium produce in a flame test?
Crimson red.
What color flame does sodium produce?
Yellow.
What color flame does potassium produce?
Lilac.
What color flame does calcium produce?
Orange-red.
What color flame does copper produce?
Green.
What happens when sodium hydroxide (NaOH) is added to a solution containing aluminum ions (Al³⁺)?
A white precipitate forms, which dissolves in excess NaOH.
What happens with calcium ions (Ca²⁺) or magnesium ions (Mg²⁺) when NaOH is added?
A white precipitate forms, but it does not dissolve in excess NaOH.
What happens with copper(II) ions (Cu²⁺) when NaOH is added?
A blue precipitate forms.
What happens with iron(II) ions (Fe²⁺) when NaOH is added?
A green precipitate forms.
What happens with iron(III) ions (Fe³⁺) when NaOH is added?
A brown precipitate forms.
How do you test for carbonate ions?
Add a dilute acid (e.g., HCl). If carbonate ions are present, carbon dioxide gas is produced, which turns limewater cloudy.
How do you test for halide ions?
Add dilute nitric acid to remove carbonate impurities, then add silver nitrate solution. The color of the precipitate indicates the halide ion present.
What precipitate forms if chloride ions (Cl⁻) are present in the halide test?
A white precipitate of silver chloride forms.
What precipitate forms if bromide ions (Br⁻) are present in the halide test?
A cream precipitate of silver bromide forms.
What precipitate forms if iodide ions (I⁻) are present in the halide test?
A yellow precipitate of silver iodide forms.
How do you test for sulfate ions (SO₄²⁻)?
Add dilute hydrochloric acid, followed by barium chloride solution. A white precipitate of barium sulfate forms if sulfate ions are present.
How do you test for ammonia gas (NH₃)?
Expose damp red litmus paper to the gas. If ammonia is present, the paper turns blue.
How do you test for hydrogen gas?
Place a lit splint near the gas. A squeaky pop indicates hydrogen.
How do you test for oxygen gas?
Insert a glowing splint. It will relight in oxygen.
How do you test for carbon dioxide gas?
Bubble the gas through limewater. It will turn cloudy if CO₂ is present.
How do you test for chlorine gas?
Damp litmus paper is bleached white in chlorine gas.
What are the advantages of instrumental methods over chemical tests?
Instrumental methods are faster, more sensitive, and more accurate.
How does flame emission spectroscopy work?
A sample is heated in a flame, and the light emitted is analyzed with a spectrometer. The wavelength of light identifies the metal ion, and the intensity indicates the concentration.
