Structure

Atom: The smallest, unbreakable part of an element.
Molecule: Two or more atoms chemically bonded (simple molecular).
Element: A substance that contains one type of atom.
Compound: A substance that contains two or more types of chemically bonded atoms.
Mixture: A substance that has two or more types of elements and/or compounds that are not chemically bonded.

SUBSTANCE	STRUCTURE
Elements	Atoms
Compounds	Molecules
Mixtures	Lattice

What are These Mixtures of?

Molecules of a compound + Molecules of an element

Atoms of an element + molecules of an element

Atoms of an element + molecules of a compound

- A pure substance has a fixed melting/boiling point, but a mixture may melt/boil over a range of temperatures.

Separating methods

Key Terms:

Solvent: The liquid that a solute dissolves in. E.g., water.
Solute: The solid that dissolves in a solvent. E.g., salt.
Solution: When a solute dissolves in a solvent, a mixture (always clear) forms. E.g., saltwater.
Soluble: A solid that can dissolve in a liquid.
Insoluble: A solid that cannot dissolve in a liquid.
Miscible: Two liquids that can mix.
Immiscible: Two liquids that cannot mix.
Saturated solution: A solution in which the max. amount of solute has been dissolved.

Filtration:

- This device is used to separate mixtures of insoluble solids and solvents/solutions.
- For instance, it can be used to separate mixtures such as sand and water.
- Separates: Insoluble solid from a solid and a liquid from an insoluble solid.

Evaporation:

- This device is used to separate mixtures of insoluble solids and solvents/solutions.
- For instance, it can be used to separate mixtures such as sand and water.
- Separates: Insoluble solid from a solid and a liquid from an insoluble solid.

Distillation:

- It is used to separate mixtures of soluble solids and solvents. It allows you to keep the solute (solid) and solvent.
- E.g., alcohol from sugar dissolved in alcohol.
- Separates: Solvent from a solution.

Separating Funnel:

- It enables the separation of two immiscible liquids, such as oil and water.
- You can first let out the less dense liquid and then the denser one.

Fractional Distillation

- This is a way to separate a mixture of miscible liquids whose boiling points are different. You can use it for multiple liquids.

Example: Ethanol and water

1) The mixture is heated. At about 78°C, the ethanol begins to boil. Some water evapourates at that temperature too, so a mixture of ethanol and water vapour rises up the column.
2) The vapours condense on the glass beads in the column, making them hot.
3) When the beads reach about 78°C, ethanol vapour no longer condenses. Only vapourised water does that. So the water vapour drips back into the flask, while the ethanol vapour goes into the condenser, where it's cooled, condenses to a liquid, and drips into the beaker.
4) After distilling all the ethanol, the temperature will increase.

Chromatography

- It is used to separate a mixture of soluble solids/solutes, such as dyes, inks, or blood.

- Avoid placing the ink spot in the solvent, as it will dissolve and not move up the paper.
- The origin line must be drawn in pencil so the line doesn't merge with the ink.
- It would be preferable to carry out chromatography in a sealed container so the solvent doesn't evaporate.
- Water is the solvent for the ink in felt-tip pens. Does the paper absorb the water? The water dissolves and separates the various pigments in the ink, then transports them up the paper. However, some solutes are more soluble than others, allowing them to travel further up the paper. An ink particle will travel further in a given amount of time if it attaches itself to a water particle more strongly. Chromatography only works if the test mixture is soluble in the solvent. E.g., biros aren't soluble in water, so use another solvent.

Rf Values:

Copper Sulfate

- Copper oxide reacts with sulphuric acid to form blue copper sulfate crystals. Filtration and evapouration/crystallisation can separate the crystals.

Equations:

Word: Copper (II) oxide + sulfuric acid → Copper (II) sulfate + water.

Symbol: CuO (s) + H₂SO₄ (aq) → CuSO₄ (aq) + H₂O (l).

Steps:

1) Warm dilute SO₄²⁻ acid; while stirring, add CuO until all the acid has been neutralised and the CuO remains in excess—a black solid.
→ To speed up the process, use a warm-over Bunsen burner. When the CuO stops disappearing, we know the acid has neutralised.

2) Filter the mixture—the filtrate is a bright blue solution. Then pour the solution into an evapourating basin.

3) Then heat the evapourating basin until a saturated salt solution forms. (Heat to remove 2/3 of water.)
→ We heated the solution to remove some of the water and obtain a saturated solution.
→ Saturated crystals will start to form on the edge of the evapourating basin.

4) Leave your solution to cool and crystallise, then filter off the crystals from the filtrate and dry them between filter papers.
→ While you don't 'heat to dryness' by removing all the water, crystals require some water to form.

If a glass rod was dipped into the solution and then removed, crystals will rapidly form on the surface of the glass rod when the hot saturated solution cools.