MATERIALS MODULE 01a (ii) PARTICULATE NATURE OF MATTER

The particulate nature of matter

Demonstrate understanding of the terms atom and molecule. An tom is a single particle (although it is made up of sub particles) Molecules are made up of several atoms These can be the same or different.

ATOMIC THEORY Everything is made up of either atoms or molecules Molecules are made of atoms Atoms are made up of three small particles

Elements, compounds and mixtures

Describe the differences between elements, compounds and mixtures elements.html elements.html

An element consists of only one kind of atom, cannot be broken down into a simpler type of matter by either physical or chemical means, can exist as either atoms (e.g. argon - Ar) or molecules (e.g., nitrogen – N 2 ).

A compound consists of atoms of two or more different elements bound together, can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), has properties that are different from its component elements, and always contains the same ratio of its component atoms.

A mixture consists of two or more different elements and/or compounds physically intermingled, can be separated into its components by physical means, and often retains many of the properties of its components.

Demonstrate understanding of the concepts of element, compound and mixture ence/chemical_material_behaviour/compoun ds_mixtures/activity.shtml ence/chemical_material_behaviour/compoun ds_mixtures/activity.shtml

Physical and chemical changes

Identify physical and chemical changes, and understand the differences between them A chemical change makes a substance that wasn't there before. There may be clues that a chemical reaction took place, such as light, heat, colour change, gas production, odour, or sound. The starting and ending materials of a physical change are the same, even though they may look different.

Chemical changes take place on the molecular level. produce a new substance. Examples of chemical changes include  combustion (burning),  cooking an egg,  rusting of an iron pan,  mixing hydrochloric acid and sodium hydroxide to make salt and water.

Physical changes are concerned with energy and states of matter. do not produce a new substance. Examples are are changes in state or phase (melting, freezing, vaporization, condensation, sublimation) Examples of physical changes include  crushing a can,  melting an ice cube,  breaking a bottle.

Experimental techniques

ence/chemical_material_behaviour/compoun ds_mixtures/revise9.shtml ence/chemical_material_behaviour/compoun ds_mixtures/revise9.shtml This is a very good website

Describe paper chromatography. Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food.

The colours separate and move up the paper at different rates

Interpret simple chromatograms. Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, eg water. As the solvent soaks up the paper, it carries the mixtures with it. Different components of the mixture will move at different rates. This separates the mixture out.

The same substance will always move the same distance if the same solvent is used Chromatography can be used to analyse which substances are present in a mixture

Describe methods of separation and purification: filtration, crystallisation, distillation, fractional distillation Mixtures of liquids can be separated according to their properties. The technique used depends on whether the liquids dissolve in each other, and so are miscible, or if they are immiscible. Fractional distillation is a technique used to separate liquids according to their boiling points.

Immiscible liquids Immiscible means that the liquids don't dissolve in each other – oil and water are an example. It is possible to shake up the liquids and get them to mix but they soon separate. Separating immiscible liquids is done simply using a separating funnel. The two liquids are put into the funnel and are left for a short time to settle out and form two layers. The tap of the fun nel is opened and the bottom liquid is allowed to run. The two liquids are now separate

Separating immiscible liquids is done simply using a separating funnel. The two liquids are put into the funnel and are left for a short time to settle out and form two layers. The tap of the funnel is opened and the bottom liquid is allowed to run. The two liquids are now separate

Miscible liquids Miscible liquids are harder to separate as they dissolve in each other. Miscible liquids are often separated using fractional distillation. This is possible as miscible liquids have different boiling points.

Ethanol and water Simple distillation can be used to separate these The ethanol evaporates then condenses It is then collected Water remains in the flask

Fractional distillation of liquid air Air is cooled Water vapour condenses, and is removed using absorbent filters Carbon dioxide freezes at – 79ºC, and is removed Oxygen liquefies at –183ºC Nitrogen liquefies at –196ºC The liquid nitrogen and oxygen are then separated by fractional distillation.

A mixture of a solid and a liquid These can be separated by filtration learningcommunity/sciences/scie nce10/curr_content/science10/un ita/redon17.html learningcommunity/sciences/scie nce10/curr_content/science10/un ita/redon17.html

Vacuum-filtration Very fine filter paper can be used Very small particles filtered out Pulling air through the residue will dry it out.

A dissolved substance can be removed by crystallisation

Chromatography

Filtration

Crystallisation

Simple distillation Separating a liquid from a solution

Identify substances and assess their purity from melting point and boiling point information. The melting point of a solid is constant Substances have unique melting points, which are measured and recorded An impure substance's melting point will differ slightly from that of the pure substance. Heating a solid substance, and marking the exact temperature at which it melts, is a simple way to test the purity of the compound. Much like solids, liquids can be tested with the application of heat. The boiling point of liquid substances is constant To determine the purity of a liquid substance, chemists measure the exact temperature at which the liquid begins to boil and compare it with the pure substance's constant boiling point

Fractional distillation

Suggest suitable purification techniques, given information about the substances involved You need to be able to apply these techniques to appropriate situations

Understand the importance of purity in substances in everyday life, e.g. foodstuffs and drugs. A pure compound contains a single chemical and is not polluted with any other chemical or element. Calculating the purity of a substance is particularly important for medicinal substances, as impurities could injure or kill patients. Substances with significant impurities may produce unexpected reactions in a laboratory setting, creating toxic or flammable compounds.