IGCSE Chemistry Unit 1: States of Matter PDF

Unit 1 STATES OF MATTER IGCSE CHEMISTRY Q: What is “Matter”?  Matter is anything that has mass and volume filling a space.  All matter is made of tiny particles (atoms, ions and molecules). States of matter:  Matter exists in three states: solid, liquid and gas.  They a...

Unit 1 STATES OF MATTER IGCSE CHEMISTRY Q: What is “Matter”?  Matter is anything that has mass and volume filling a space.  All matter is made of tiny particles (atoms, ions and molecules). States of matter:  Matter exists in three states: solid, liquid and gas.  They are interconnected through cooling and heating. Melting point (m.p): the temperature at which a solid turns into a liquid- it has the same value as the freezing point; a pure substance has a sharp melting point Evaporation: a process occurring at the surface of a liquid, involving the change of state from a liquid into a vapour at a temperature below the boiling point Pure substance: a single chemical element or compound- it melts and boils at definite precise temperature Lattice: a regular three-dimensional arrangement of atoms, molecules or ions in a crystalline solid Table: Melting and boiling points of some common chemical substances Substance Physical state Melting point/℃ Boiling point/℃ at room temperature (25℃) Oxygen Gas -219 -183 Nitrogen Gas -210 -196 Ethanol Liquid -117 78 (alcohol) Water Liquid 0 100 Sulphur Solid 115 444 Common salt Solid 801 1465 (Sodium chloride) Copper Solid 1083 2600 Carbon dioxide gas -78* *Sublimes at atmospheric pressure Table: differences in the properties of the three state of matter A substance’s melting and boiling points in relation to room temperature (taken as 20℃) determine whether it is usually seen as a solid, a liquid or a gas. For example: Fig: Applying the kinetic model to changes in physical states Changing the external pressure on a sample of a gas produces a change in volume that can easily be seen.  An increase in external pressure produces a contraction in volume. The gas is compressed.  A decrease in external pressure produces an increase in volume. The gas expands. The volume of a gas is also altered by changes in temperature.  An increase in temperature of a gas produces an increase in volume. The gas expands.  A decrease in temperature of a gas produces a decrease in volume. The gas contracts. The key points about the processes taking place during condensation and freezing are:  As the particles come closer together, new forces of interaction take place  This means that energy is given out during these changes  Therefore, the temperature remains unchanged until the liquid or solid is totally formed. Fig: The energy changes taking place during heating and cooling Exothermic changes: a process or chemical reaction in which heat energy is produced and released to the surroundings. ΔH for an exothermic change has a negative value. Endothermic changes: a process or chemical reaction that takes in heat from the surroundings. ΔH for an endothermic change has a positive value. Intermolecular forces: the weak attractive forces that act between molecules. Mixture: two or more substances mixed together but not chemically combined- the substances can be separated by physical means Solution: is formed when a substance (solute) dissolves into another substance (solvent) Solute: the solid substance that has dissolved in a liquid (the solvent) to form a solution Solvent: the liquid that dissolves the solid to form a solution; water is the most common solvent but liquids in organic chemistry that can act as solvents are called organic solvents Suspension: A mixture containing small particles of an insoluble solid, or droplets of an insoluble liquid, spread (suspended) throughout a liquid Precipitation reaction: a reaction in which an insoluble salt is prepared from solutions of two soluble salts Fig: When solute dissolves in a solvent, the solute particles are completely dispersed in the liquid. Soluble: a solute that dissolves in a particular solvent Insoluble: a substance that does not dissolve in a particular solvent Miscible: if two liquids form a completely uniform mixture when added together, they are said to be miscible Alloys: mixtures of elements (usually metals) designed to have the properties useful for a particular purpose, e.g. solder (an alloy of tin and lead) has a low melting point Saturated solution: A solution that contains as much dissolved solute as possible at a particular temperature Concentration: a measure of how much solute is dissolved in a solvent to make a solution. Solutions can be dilute (with a high proportion of solvent), or concentrated (with a high proportion of solute) Solubility: a measure of how much of a solute dissolves in a solvent at a particular temperature The Brownian Motion: by Robert Brown  It is the random motion of particles in a suspension which can be seen by the eye or under a microscope and this motion is because the particles follow a zigzag pattern because they are struck by tiny invisible particles.  e.g. cooking smell due to tiny particles which spread because they are bombarded by particles in air.  This is also an example of diffusion. e.g. the random motion of dust particles in air is due to their bombardment by gas molecules. Fig: a Diffusion of an individual gas molecule or atom; the particle collides with many others, deflecting its path. b Demonstrating Brownian motion using a smoke cell, the smoke particles show a random motion. https://youtu.be/lFh_VxIAQWA The Kinetic Particles Theory: (Motion Theory)  All matter is made up of very small invisible particles (atoms, ions & molecules). (OR) All matter is divided into very small particles known as atom.  Each element is composed of its own type of atom.  Atoms of different elements can combine to make the molecules of a compound.  The speed of the particles depends on their mass and temperature.  So the higher the temperature the faster the particles will move.  Also lighter particles will move faster than the heavier ones.  Gases can fill any volume as they are free to move anywhere. The following graph shows the changing of state (Heating curve) from solid (ice) to liquid (water) to gas (steam).  At point A: solid is heated. Its particles get more energy so they vibrate more.  At point B: (change of state happens) particles have gained enough heat energy to break the strong force between the particles. At that point melting occurs and the temperature remains constant until all the solid ice change into liquid water.  At point C: water/ liquid is gaining more energy and sliding past each other more but boiling has not started yet. N.B.: some evaporation might happen at this phase.  At point D: (change of state happens) all water particles have gained enough heat energy to break forces between liquid molecules and change into gas molecules.  At that point boiling occurs and the temperature remains constant until all liquid (water) changed in gas (water vapor) at 100 °C. Workout :Draw cooling curve State Changes & its Reverse:  Melting point: the temperature at which solid melts and changes into liquid - it has the same value as the freezing point; a pure substance has a sharp melting point  Freezing/ solidification: when liquid is cooled, particles slow down and eventually stop moving changing into solid.  Boiling point: temperature at which liquid changes/ boils into gas. State Changes & its Reverse:  Pure substance: a single chemical element or compound- it melts and boils at definite precise temperature  Lattice: a regular three-dimensional arrangement of atoms, molecules or ions in a crystalline solid  Condensation/Liquefaction: when gas is cooled, particles lose energy, move slowly and become closer changing into liquid. Evaporation:  It is when the particles on the surface of the liquid have enough energy to escape into gaseous state and form a gas at a temperature below the boiling point.  Evaporation can occur spontaneously at any temperature but boiling occurs at a certain temperature which is the boiling point.  Rate of evaporation increases: 1)by increasing Temperature 2)by increasing Surface area Sublimation:  it is the change of state from solid to gas directly and back from gas to solid without passing through the liquid state.  e.g.: if you leave solid frozen carbon dioxide at room temperature, it sublime to carbon dioxide gas(called dry ice).  e.g.: if you boil dark grey iodine crystal(solid) it changes into purple vapor I2 gas and on cooling returns back to dark grey iodine crystal. Important points to be mentioned during change of state: 1. Particles gain heat move faster and collide more and more of colliding molecules have sufficient energy/activation energy to react. 2. Pure substances have fixed melting and boiling points. Presence of impurities increase boiling point and decrease the melting point. e.g.: pure water boils at 100 °C and freezes at 0°C. 3. The melting and boiling points of different substances reflect the strength of attraction between the molecules of these substances. 4. Compressing a gas: the only particles that can be compressed are gas particles while solid and liquid cannot be compressed because their particles are already very close together. If enough force is applied by the plunger the gas particles get closer together and changes into liquid.  When the gas is compressed into smaller space, its pressure increases, and by heating the gas in a closed container it’s pressure increases.  This is the idea of the pressure cooker. Note: Pressure is created from the beginning as gas particles hit each other and hit the side of the container so this exerts pressure. Diffusion  Particles move from region of high concentration into region of low concentration down concentration gradient. (OR)  The process by which different fluids mix due to the random motions of their particles.  The main ideas involved in diffusion are: Particles move from a higher concentration region towards a lower concentration region; eventually, the particles are evenly spread. Their concentration is the same throughout. The rate of diffusion in liquids is much slower than in gases. Diffusion does not occur in solids as the particles cannot move from place to place. e.g.: 1) Bromine diffusion: Bromine is a reddish brown liquid that easily vaporizes (turns into gas) at room temperature. Some bromine is placed at the bottom of a sealed jar as the cover in the middle of the jar removed the reddish brown vapor of Bromine diffuses to fill both sides uniformly. Figure: Bromine vapour diffuses throughout the container to fill the space available Figure: Ammonia and hydrochloric acid fumes diffuse at different rates 2) Solid crystals dissolve and spread among water particles. e.g.: Blue Copper Sulfate crystals and purple Potassium Manganate (VII) 3) Perfume smells/ Car exhausts/ Drops of ink in water The rate of diffusion of gases depends on the molecular mass (Mr) and the temperature. The smaller the Mr, the faster they diffuse. The higher the temperature, the faster they diffuse. (liquids and gases only) The important points derived from the kinetic particle theory relevant here are: Heavier gas particles move more slowly than lighter particles at the same temperature Larger molecules diffuse more slowly than smaller ones The rate of diffusion is inversely related to the mass of the particles The average speed of the particles increases with an A) The mass of the molecules: - Cotton wool soaked in Ammonia solution is put into one end of a long tube which gives off Ammonia gas NH3. - At the same time, in the same tube, a cotton wool soaked in Hydrochloric acid (HCl) is put into the other end which gives of Hydrogen Chloride gas. - The gases diffuse along the tube reacting together forming white smoke of Ammonium chloride NH4Cl where they meet. - Ammonia NH3 (14+3=17) particles have lower mass so they travel faster than Hydrogen Chloride HCl(1+35.5=36.5) - The white smoke NH4Cl is formed closer to Hydrochloric acid B. - The lower the relative molecular mass, the faster the gas diffuses. B) The temperature: - When a gas is heated, its particles take in heat energy and move faster. - They collide with more energy so the gas diffuses faster. Applications of Diffusion:  Separation of a mixture of gases by diffusion at a certain temperature: e.g.: 1) Helium and Argon mixture 2) Oxygen O2 and Ozone O3 1. Which gas has the fastest rate of diffusion? 2. Samples of four gases are released in a room at the same time. The gases are carbon dioxide, CO2, hydrogen chloride, HCl, hydrogen sulfide, H2S, and nitrogen dioxide, NO2. Which gas diffuses fastest? A. carbon dioxide B. hydrogen chloride C. hydrogen sulfide D. nitrogen dioxide C. Hydrogen sulfide 3. The graph shows the change in temperature as a sample of a gas is cooled. Name the change of state taking place between A and B. 4. A bottle of liquid perfume is left open at the front of a room. After some time, the perfume is smelt at the back of the room. Name the two physical processes taking place. 3. Condensation 4. evaporation and diffusion  4. A substance boils at temperature X and melts at temperature Y. Complete the graph to show the change in temperature over time as the substance cools from temperature A to temperature B. (a) A solution is a mixture of a solute and a solvent. (b)(i) Name the process when a solid substance mixes with a solvent to form a solution........................................................................................................................................ (c)(ii) Name the type of reaction when two solutions react to form an insoluble substance...............................................................................................................................