Chemical analysis

What is a pure substance?

• A substance made up of only one element or compound.

• Has a fixed boiling/melting point.

What is a mixture?

• Contains two or more substances not chemically bonded.

• Boiling/melting points vary over a range.

How can melting/boiling point tell us about purity?

• Pure substances have sharp melting/boiling points.

• Impurities lower melting point and increase boiling point range.

What is a formulation?

• A mixture with exact amounts of components designed for a specific purpose.

• Examples: fuels, paints, medicines, cleaning agents.

Why are formulations important in products like medicine?

• The proportion of each component affects the function and safety of the product.

What is chromatography used for?

To separate mixtures and identify substances.

What is the stationary phase and mobile phase in paper chromatography?

• Stationary phase = Paper (doesn't move)

• Mobile phase = Solvent (moves through paper)

How does chromatography work?

Different substances have different solubilities and attractions to the paper, so they move at different speeds.

What is the Rf value and how is it calculated?

• Rf = Distance moved by substance ÷ Distance moved by solvent

• Rf is always <1

How can chromatography identify substances?

• Compare Rf values to known substances (under same conditions).

Test for hydrogen gas

Insert a lit splint → ‘Squeaky pop’ sound.

Test for oxygen gas

Insert a glowing splint → Relights.

Test for carbon dioxide

Bubble through limewater → Turns cloudy (forms calcium carbonate).

Test for chlorine gas

• Damp blue litmus paper → Turns red then white (bleached).

Flame test for lithium (Li⁺)

Crimson red flame

Flame test for sodium (Na⁺)

Yellow flame.

Flame test for potassium (K⁺)

Lilac flame.

Flame test for calcium (Ca²⁺)

Orange-red flame.

Flame test for copper (Cu²⁺)

Green flame.

Aluminium (Al³⁺) + NaOH

White precipitate, dissolves in excess NaOH

Calcium (Ca²⁺) + NaOH

White precipitate, does NOT dissolve in excess.

Magnesium (Mg²⁺) + NaOH

White precipitate, does NOT dissolve in excess.

Copper (Cu²⁺) + NaOH

Blue precipitate of copper(II) hydroxide.

Iron (Fe²⁺) + NaOH

Green precipitate of iron(II) hydroxide.

Iron (Fe³⁺) + NaOH

• Brown precipitate of iron(III) hydroxide.

Test for carbonate ions (CO₃²⁻)

Add dilute acid → Fizzing (CO₂ gas). Confirm with limewater test.

Test for sulfate ions (SO₄²⁻)

Add dilute HCl then barium chloride solution → White precipitate (barium sulfate).

Test for halide ions (Cl⁻, Br⁻, I⁻)

Add dilute nitric acid, then silver nitrate solution:

• Chloride → White precipitate (AgCl)

• Bromide → Cream precipitate (AgBr)

• Iodide → Yellow precipitate (AgI)

What are instrumental methods?

Accurate, sensitive, and rapid chemical analysis using machines.

What is flame emission spectroscopy?

An instrumental method for identifying metal ions in a solution.

How does flame emission spectroscopy work?

• Sample put in a flame → electrons become excited → emit light.

• Light is analysed as a line spectrum.

What can the line spectrum tell us?

• Position of lines = identity of metal ion

• Intensity of lines = concentration of metal ion

Why are instrumental methods used?

• Faster and more accurate

• Can detect very small amounts

• Can identify mixtures and give quantitative data