IGCSE(A*-G) Edexcel - Chemistry

Transcription

1 IGCSE(A*-G) Edexcel - Chemistry Principles of Chemistry States of Matter NOTES

2 1.1 Understand the arrangement, movement and energy of the particles in each of the three states of matter: solid, liquid and gas State of matter Solid e.g. ice Liquid e.g. water Gas e.g. water vapour Particles in substance Spacing between particles Close together and touching each other Close together and touching each other Far apart Arrangement of particles Regular, repeating pattern Irregular Irregular Movement of particles Vibrate about fixed positions but do not move apart Move around and slide past one another Move freely and collide with each other Forces between particles Stronger than in liquid Not as strong as solid Non-existent Shape Fixed shape and volume No fixed shape (takes shape of container) but fixed volume No fixed shape or volume

3 1.2: Understand how the interconversions of solids, liquids and gases are achieved and recall the names used for these interconversions Definitions: Melting: The process of converting from solid to liquid due to increase of temperature. Melting point: The temperature at which a solid starts to melt. Ice melts at 0 C. Boiling: The process of converting from liquid to gas due to increase of temperature. Can also be called vaporisation. Boiling point: The temperature at which liquid starts to boil. Water boils at 100 C. Condensation: The process by which a gas turns to a liquid, this process is called condensation. Sublimation: The process by which a solid directly turns into a gas without melting. Solidification: The process at which gas directly turns to solid. Evaporation: A process by which a liquid turns to a gas below its boiling point. Volatile: The liquids which evaporates at room temperature are called volatile.

4 Changes in arrangement, movement and energy of particles during these interconversions: Solid liquid: Heat solid until it melts. When a solid is heated the particles gain kinetic energy and start to vibrate faster about their fixed position. When the temperature is high enough, the vibration of the particles become sufficient to overcome the forces of attraction between them. The particles begin to break away from their regular pattern. The particles can now slide past each other. The solid becomes a liquid. Liquid solid: Cool liquid until it freezes. When a liquid is cooled, the kinetic energy is lost by the particles. When the temperature is low enough, the particles no longer have the energy to slide over each other. The forces of attraction can hold the particles together in a regular pattern. The particles can no longer slide past one another, the substance becomes a solid. Liquid Gas: Heat the liquid until it boils. When a liquid is heated, the particles gain kinetic energy and move further apart. Eventually the attractive forces in the liquid are all broken. Bubbles of gaseous particles escape from the liquid. The substance becomes a gas. Gas liquid: Cool the gas until it condenses. When a gas is cooled the particles lose kinetic energy and allows the attractive forces to hold the particles closer together as a liquid. The gas is now condensed to liquid. Solid gas: Heat the solid until it sublimes. The solid particles gain kinetic energy and vibrate faster. Eventually the forces of attraction between particles are completely broken and they escape from the solid as a gas.

5 1.3: Understand how the results of experiments involving the dilution of coloured solutions and diffusion of gases can be explained Diffusion and dilution experiments support a theory that all matter (solids, liquids and gases) is made up of tiny, moving particles. Diffusion experiment Diagram showing the diffusion of red-brown bromine gas from one jar into another Diffusion of bromine gas from one flask to another. After 5 minutes the bromine gas has diffused from the bottom flask to the top flask. Explanation: The air and bromine particles are moving randomly and there are large gaps between particles. The particles can therefore easily mix together.

6 Diffusion experiment Diagram showing the diffusion of potassium manganite in water over time When potassium manganate (VII) crystals are dissolved in water a purple solution is formed. A small amount of crystals produce a highly intense colour. Explanation: The water and potassium manganate (VII) particles are moving randomly and the particles can slide over each other. The particles can therefore easily mix together. Diffusion in liquids is slower than in gases because the particles in a liquid are closely packed together and move more slowly. Dilution of coloured solutions When potassium manganate (VII) crystals are dissolved in water, the solution can be diluted several times. The colour fades but does not disappear until a lot of dilutions have been done. This indicates that there are a lot of particles in a small amount of potassium manganate (VII) solid. This indicates that the particles must be very small.

7 1.4: Know what is meant by the terms: Term Meaning Example Solvent Solute Solution Saturated solution Soluble Insoluble The liquid in which a solute dissolves The substance which dissolves in a liquid to form a solution The mixture formed when a solute in dissolved in a solvent A solution with the maximum concentration of solute dissolved in the solvent Describes a substance that will dissolve Describes a substance that won t dissolve The water in sea water The salt in sea water Sea water Sea water in the dead sea Salt is soluble in water Sand is insoluble in water 1.5C: Know what is meant by the term solubility in the units g per 100 g of solvent Different substances have different solubilities. Solubility of a solute can be expressed in g per 100 g of solvent. Solubility of solids is affected by temperature. As temperature increases solids become more soluble. Solubility of gases is affected by temperature and pressure. As pressure increases gases become more soluble. As temperature increases gases become less soluble, in general. 1.6C: Understand how to plot and interpret solubility curves Solubility graphs represent solubility in grams per 100 g of water plotted against temperature. To plot a solubility curve the maximum mass of solvent that can be dissolved in 100 g of water, before a saturated solution is formed, is determined at a series of different temperatures.

8 Solubility graph for salts Example question 1: How much potassium nitrate will dissolve in 20g of water at 34 C? At 34 C the solubility is 52g per 100g of water So scaling, 52 x 20 / 100 = 10.4 g of potassium nitrate will dissolve in 20 g of water. Example question 2: 200 cm 3 of saturated copper solution was prepared at a temperature of 90 C. What mass of copper sulphate crystals form if the solution was cooled to 20 C? Solubility of copper sulphate at 90oC is 67g/100g water, and 21g/100g water at 20 C. Therefore for mass of crystals formed = = 46g (for 100 cm 3 of solution). However, 200 cm 3 of solution was prepared, So total mass of copper sulphate crystallised = 2 x 46 = 92g

9 Solubility graph for gases Unlike salts, in the previous graph, gases become less soluble as temperature increases. E.g. fizzy drinks become flat more quickly when left at a warmer temperature.

10 1.7C: Practical: investigate the solubility of a solid in water at a specific temperature Solubility experiment Method: Take known volume of water and heat to specific temperature, e.g. in a water bath set to desired temperature. Keep thermometer in water to make sure temperature is maintained throughout. Add known masses of solvent bit by bit, until saturated solution formed when solid stops dissolving and remains as solid in solution. Record mass of solid that was soluble Repeat with different temperature Can plot solubility curve as seen above.