Chemical Tests – Vocabulary Flashcards

Vocabulary cards covering key chemical tests, observations, flame colours, equations and safety notes from the lecture.

Iron(II) hydroxide

Green precipitate formed when Fe²⁺ ions react with OH⁻

Iron(III) hydroxide

Orange-brown precipitate formed when Fe³⁺ ions react with OH⁻

Oxidation of Fe(OH)₂

Green Fe(OH)₂ darkens to orange-brown Fe(OH)₃ on standing in air

Test for Iron(II) ions

Add NaOH(aq); green Fe(OH)₂ precipitate confirms Fe²⁺

Test for Iron(III) ions

Add NaOH(aq); orange-brown Fe(OH)₃ precipitate confirms Fe³⁺

Test for Copper(II) ions (NaOH)

Add NaOH(aq); blue Cu(OH)₂ precipitate shows Cu²⁺

Test for Ammonium ions

Warm with NaOH; alkaline NH₃ gas produced turns damp red litmus blue

Ammonia gas (NH₃)

Pungent, alkaline gas that turns moist red litmus paper blue

Safe smelling of ammonia

Waft gently only when cold; avoid if asthmatic or if mixture is warm

Why test solutions not solids

Solid samples already opaque; precipitate formation cannot be seen

Flame test – lithium

Crimson-red flame indicates Li⁺ ions

Flame test – sodium

Yellow/orange flame indicates Na⁺ ions

Flame test – potassium

Lilac flame indicates K⁺ ions

Flame test – calcium

Orange-red flame indicates Ca²⁺ ions

Flame test – copper(II)

Blue-green flame indicates Cu²⁺ ions

Soluble hydroxides

Only NaOH, KOH and NH₄OH are appreciably soluble in water

Test for carbonates

Add dilute acid; effervescence gives CO₂ which turns limewater cloudy

Carbonate ionic equation

CO₃²⁻ + 2H⁺ → CO₂ + H₂O

Test for sulfates

Acidify with HCl, add BaCl₂; white BaSO₄ precipitate shows SO₄²⁻

Reason for acidifying sulfate test

Acid removes interfering anions (e.g., CO₃²⁻) that also form white solids

Acid not used for sulfate test

Do not use H₂SO₄; it introduces sulfate ions giving false positive

Test for chloride ions

Acidify with HNO₃, add AgNO₃; white AgCl precipitate forms

Test for bromide ions

Acidify, add AgNO₃; cream AgBr precipitate forms

Test for iodide ions

Acidify, add AgNO₃; yellow AgI precipitate forms

Colour of AgCl

White precipitate

Colour of AgBr

Cream precipitate

Colour of AgI

Yellow precipitate

Test for water (chemical)

White anhydrous CuSO₄ turns blue when water present

CuSO₄ colour change

CuSO₄ (white) + 5H₂O → CuSO₄·5H₂O (blue)

Test for pure water (physical)

Pure water freezes at 0 °C and boils at 100 °C at 1 atm

Test for hydrogen gas

Lit splint gives a squeaky pop as H₂ burns to form water

Test for oxygen gas

Glowing splint relights in O₂

Test for carbon dioxide gas

CO₂ turns limewater milky due to CaCO₃ formation

Limewater reaction

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (white precipitate)

Test for chlorine gas

Damp litmus/universal paper turns red then white (bleached)

Bleaching sequence

Cl₂ first acidifies (red) then bleaches (white) the damp indicator

Chlorine safety

Avoid inhalation; wear eye protection and do not sniff directly

Ammonia – only alkaline gas in syllabus

Among common lab gases, NH₃ is uniquely alkaline, aiding identification