Chemistry Chemical Analysis

What defines a pure substance in chemistry?

A single element or compound not mixed with any other substance.

How can you determine the purity of a substance?

By measuring its melting or boiling point and comparing it to the known value of the pure substance.

What is a formulation?

A mixture designed as a useful product, made by mixing components in precise quantities to ensure desired properties.

Give three examples of formulations.

Fuels, cleaning agents, paints.

What is chromatography used for?​

To separate mixtures and identify substances within them.

In paper chromatography, what is the stationary phase and mobile phase?

Stationary: Solvent paper

Mobile: Solvent

How do substances separate in chromatography?​

Based on their different attractions to the stationary and mobile phases.

How do you test for hydrogen gas?​

Introduce a lit splint; a 'squeaky pop' sound indicates hydrogen.

How do you test for oxygen gas?

Insert a glowing splint; it will relight in the presence of oxygen.

How do you test for carbon dioxide gas?​

Bubble the gas through limewater; it turns cloudy if carbon dioxide is present.

How do you test for chlorine gas?​

Damp litmus paper turns white (is bleached) in the presence of chlorine.

What colour does lithium, sodium, potassium, calcium and copper produce in a flame test?

Lithium: Crimson

Sodium: Yellow

Potassium: Lilac

Calcium: Orange-red

Copper: Green

How can metal hydroxides be identified?

By adding sodium hydroxide solution; insoluble hydroxides form precipitates with characteristic colors.

What colour precipitate does calcium, copper(II), iron(II) and iron(III) form with sodium hydroxide?

Calcium: White

Copper(II): Blue

Iron(II): Green

Iron(III): Brown

What colour precipitate does aluminium and magnesium form with sodium hydroxide?

Aluminium: White, but dissolves in excess sodium hydroxide to form a colourless solution.
Magnesium: White, but doesn’t dissolve in excess sodium hydroxide.

How are carbonate ions (CO₃²⁻) tested for?

• Add dilute acid; carbon dioxide gas is produced.

• Confirm CO₂ using limewater (it turns cloudy).

How are sulfate ions (SO₄²⁻) tested for?

• Add hydrochloric acid (to remove carbonate interference).

• Add barium chloride; a white precipitate of barium sulfate confirms the presence of sulfate ions.

How are halide ions (Cl⁻, Br⁻, I⁻) tested for and what are the results for each?

• Add nitric acid (to remove carbonate interference).

• Add silver nitrate solution.

• Chloride: White precipitate

• Bromide: Cream precipitate

• Iodide: Yellow precipitate

What is flame emission spectroscopy and how does it work?

An analytical technique using light emitted by metal ions in a flame to determine their identity and concentration.

• Metal ions are heated in a flame.

• They emit light of specific wavelengths.

• A spectrometer detects and identifies the wavelengths.

What are the advantages of instrumental analysis like spectroscopy?

• Highly sensitive (detects very small amounts).

• Highly accurate (gives precise readings).

• Very fast (used in real-time monitoring).