C.Powell Chemistry What is Chemistry? Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions. Chemistry is the branch of science that seeks to explain the behaviour of matter on a molecular level and is considered to be “The Central Science” because it connects all the other Natural Sciences. Matter Matter is anything that has mass and takes up space (volume).Matter is practically everything and everywhere. Matter can exist in 3 distinct with specific arrangement of their particles. Fig2 showing the different states and the arrangement of their particles Matter is thought of as made up of tiny particles which are affected by heat and pressure. i.e. Temperature and pressure determines the phase. A Comparison of Solids, Liquids and Gases Property Shape Solid Fixed Volume Fixed Density Compressibility Usually high Difficult to compress Forces of attraction between the particles Kinetic energy possessed by the particles Strong Possesses small amounts of kinetic energy Movement of the particles Vibrate in a fixed position “What you do today can improve all your tomorrows” Liquid Takes shape of container it is in Fixed Usually lower than solids Can compressed very slightly by applying pressure Weaker than those between particles in a solid Possess more kinetic energy than the particles in a solid Move slowly past each other Gas Takes the shape of entire container it is in Variable- it expands to fill the container it is in Low Very easy to compress Very weak Possess large amounts of kinetic energy Move around freely and rapidly C.Powell Changing of states of matter Matter can exist is any of three states depending on the temperature. It can change from one state to another by heating or cooling, as this causes a change in the kinetic energy. When a solid is heated it usually changes state to a liquid then a gas. This occurs because the particles gain kinetic energy, move increasingly faster and further apart and the forces of attraction between them becomes weaker and weaker When a gas is cooled it usually changes state to a liquid and then a solid. This occurs because the particles lose kinetic energy, move more slowly, gets closer together and the force of attraction between them becomes increasingly stronger. N.B- kinetic energy is the energy associated with movement. Fig 2. Showing the different changes of states. Add heat Melting SOLID Freezing LIQUID Evaporation GAS Condensation Sublimation Deposition Removal of heat Some substances do not pass through the liquid phase and they are called sublimation and deposition. Some substances that go through sublimation are: Naphthalene (moth balls) Iodine Dry ice “What you do today can improve all your tomorrows” C.Powell Heating and cooling curve A heating curve is drawn when the temperature of a solid is measured in intervals as it is heated and changes state to a liquid then to a gas, the temperature is then plotted against time. A cooling curve is drawn when the temperature of a gas is measured at intervals as it is cooled and changed state to liquid then solid and the temperature is plotted against time. The melting point is the constant temperature which a solid changes state to a liquid The boiling point is the constant temperature at which the liquid changes its state into a gas The freezing point is the constant temperature at which the liquid changes its state to a solid Particulate theory The particulate theory of matter is the theory that explains the existence of different phases of matter and why they exist. This theory is based on the assumptions: All matter is made of particles (atoms and/or molecules) The particles are in constant random motion (Brownian motion) There are spaces between the particles There are forces of attraction and repulsion between the particles “What you do today can improve all your tomorrows” C.Powell Evidence to support the particulate theory of matter The processes of diffusion and osmosis provide evidence to support the fact that all matter is made of particles. Diffusion Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration until the particles are evenly distributed. Eg. 1 When pieces of cotton wool are soaked in concentrated ammonia solution and concentrated hydrochloric acid are placed simultaneously at the opposite ends of a glass tube, a white ring of ammonium chloride forms inside the tube. Ammonia solution gives off ammonia gas and hydrochloric acid gives off hydrogen chloride gas. The particles of the gases diffuse through the air inside the tube, collide and react to from ammonium chloride. Ammonia + Hydrogen Chloride Ammonium Chloride NH3(g) + HCl (g) NH4Cl (s) Eg 2 Placing syrup in a container containing water the syrup diffuses to produce a uniformed solution. The particles go between the spaces of the water particles until evenly distributed. This occurs with some crystals (solids). Eg sugar. “What you do today can improve all your tomorrows” C.Powell Osmosis Osmosis is the movement of water particles through a differentially/selectively permeable membrane (only allows certain molecules to pass through by diffusion) from an area of high concentration to one of low concentration. Eg1 Example 2 The membrane of living tissues is selectively permeable and the cytoplasm inside the cells contains about 80% water. When a strip of living tissue (such as paw-paw) is placed in water, water molecules move into the cells by osmosis. Each cell swells slightly and the strips increase in length and becomes rigid. When the strip is placed in an concentrated sodium chloride(table salt) solution, water molecules move out of the cell by osmosis. Each cell shrinks slightly and the strip decreases in length and becomes softer. Uses of osmosis 1. To control garden pests Slugs and snails are garden pests whose skin is differentially permeable and always moist. When table salt (sodium chloride) is sprinkled on slugs and nails, it dissolves in moisture around their bodies forming a concentrated solution. Water inside their bdies then move out by osmosis and into the solution. The slugs and snails 2. To preserve food Salt and sugar are used to preserve foods such as meats, fish and fruit. They both work the same way: They draw water out of the cells of the food by osmosis. This prevents the food from decaying because there is no water available in the cells for the chemical reactions which cause decay They draw water out of microorganisms (bacteria and fungi) by osmosis. This prevents the food from decaying because it inhibits the growth of the micro organisms that cause the decay. “What you do today can improve all your tomorrows”
