Experimental chemistry

Collecting gases

• Displacement of water → Insoluble in water or slightly soluble in water. As gases cannot dissolve in water, they would rise to the top of the gas jar and be collected there.

• Downward delivery→ soluble in water and denser than air

• Upward delivery → soluble in water and less dense than air.

• Using a gas syringe

Drying gases

• Concentrated sulfuric acid → Acid gases or gases that do not react with acids. Bubble gas through concentrated sulfuric acid

• Fused calcium chloride → most of the gases. Pass through fused CaCl₂

• Calcium oxide→ Alkaline gas. Pass through fused CaO

Elements definition

• are pure substances that cannot be broken down into simpler substances by any chemical methods and are made up oof only one type of atom.

Compounds definition

pure substances that are formed when 2 or more elements are chemically combined.

Mixtures

are formed when 2 or more substances are physically mixed together.

Molecules definition

Molecules consists of 2 or more atoms joined together covalently. elements exist in the form of atoms or molecules

Purity

• Pure substances is made up of only 1 substance not mixed with any others. Fixed melting and boiling points.

• Mixtures contains 2 or more substances. Melts and boils over a range of temperature.

Prescence of impurities in pure substances

• The melting point of a solid will be lowered if impurities are present. The greater the amount of impurities, the lower the melting point.

• The boiling point of a liquid will increase if impurities are present. The greater the amount of impurities, the higher the boiling point.

Chromatography

• Separate and identify the components present in coloured substances and food dyes/ in drugs/ blood in urine

• Different substances have different solubulities in the same solvent.

• More soluble substance will travel longer distance in a fix time

• A locating aganr is as substance that reacts with the substances on the chromatography paper to produce a coloured product

Filtration

• Used to separate insoluble solids from liquids.

• The filter paper contains pores that allows liquid and dissolved solids to pass through but no the insoluble solids.

Evaporation to dryness

• Evaporation can be used to separate soluble solids from the liquid.

• The solution is heated and the solid is recovered.

Crystallisation

• Used to obtain a solute from a solution except NaCl

1. Gently heat the solution to form a saturated solution.

2. Allow it to cool and crystals will be formed.

3. Filter and dry crystals between pieces of filter paper.

Simple distillation

• Used to obtain solvent from a solution

Method of separating solid/solid mixture.

• Sublimation → Heat the mixture to sublime solid 1. Collect solid 1 with inverted filter funnel. Solid 2 is left behind.

• None sublimes → Add suitable warm solvent to dissolve solid 1. Filter the mixture. Rinse residue with water. Crystallise filtrate to obtain solid 1

• Use a magnet if one of it is magnetic

Methods of separating liquid/liquid

• Immiscible → Use a separating funnel . The liquid with a higher density will sink to the bottom of the separating funnel and can be removed by turning on the tap.

• Miscible with different boiling points → Fractional distillation. The liquids are able to be separated as they have different boiling points.The liquid with the lower boiling point will boil off and will be collected first.