Session 6 Changes in Materials

Dissolving What does it mean? What happens when sugar is added to water? What happens when flour is added to water? Water can pull away some of the molecules from a sugar crystal and surround them completely so that the sugar molecules can’t be seen.

Changes of state Can be brought about by transferring energy Heat is a form of kinetic (movement) energy In the everyday world, all particles move, so all objects made of particles have heat energy. At what temperature would all movement stop? When two bodies at different temperatures are placed in contact, heat (thermal) energy will always flow from the one at the higher temperature to the one at the lower temperature, regardless of size. At an atomic level particles are always moving Heat is the energy of movement, the kinetic energy of particles At the level of an object, the total heat is the sum of the kinetic energies of all the molecules. The temperature at which all movement stops would be absolute zero, 0 K, -273°C

Changes of state Melting Evaporating Condensing Solidifying In the primary classroom what is used to demonstrate changes of state?

Examples of chemical changes Burning wood Mixing vinegar and sodium bicarbonate Rusting

Behaviour of metals Metals tend to: Be solid at room temperature Have high melting and boiling points Be good conductors of heat and electricity Be malleable (can be bent without snapping) Have strong bonds, making the metal strong and tough Be shiny when cut or polished

Metals (contd.) A few metals are magnetic – iron, nickel and cobalt. There are 88 elements in the Periodic Table which are classified as metals. Potassium is the most reactive metal, while gold is the least reactive

Acids and bases An acid is a compound which contains hydrogen, e.g. lemon juice (citric acid), vinegar (acetic acid), vitamin C (ascorbic acid) A base is a substance that neutralises an acid, producing salts and water. Bases are usually metal oxides, hydroxides and carbonates. A base that dissolves in water is an alkali, e.g. soap, washing powder, sodium bicarbonate. pH

Burning Type of chemical reaction Fuel + oxygen + heat (fire triangle) Fuel + oxygen carbon dioxide + water + heat

Geological changes These happen over millions of years Earth consists of three main layers : core + mantle + crust The crust is made of rock. Rock is made of minerals, naturally occurring chemical compounds.

Types of rock formation Three main types: Igneous Sedimentary Metamorphic Igneous – from molten rock / magma Sedimentary – deposited as layers of sediment; cemented together by crystals and hardened; fossils 1000 years per 1cm rock; weathering and erosion Formation When a river reaches a lake or the sea, its load of transported rocks settles to the bottom. We say that the rocks are deposited. The deposited rocks build up in layers, called sediments. This process is called sedimentation. The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. The water is squeezed out from between the pieces of rock and crystals of different salts form. The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation. These processes eventually make a type of rock called sedimentary rock. It may take millions of years for sedimentary rocks to form. These are the different processes in order: sedimentation     compaction     cementation Metamorphic – igneous and sedimentary rock changed by heat and pressure, e.g. marble and metamorphic limestone