Section 11 Chemistry

• There are 3 states of matter: Solids. Liquids and Gases. The properties of each state depend how strong the forces between each particle are.
• Solids: There are strong forces of attraction between particles. This holds them in fixed positions. The particles can't move around, they can only vibrate which means they have a definite shape and volume. Solid particles don't have much energy. The hotter the solid gets the more the particles vibrate. This causes solids to expand when heated.
• Liquids: There is some attraction between the particles. They're free to move past each other but tend to stick together. Liquids don't have a definite shape, but they keep the same volume. They will flow to fill the bottom of a container. Particles have more energy in the liquid state than in the solid state. They have less energy than the gas state. The particles are moving all the time. The hotter the liquid gets the faster they move.
• Gases: There is almost no attraction between the particles. They're free to move. They travel in straight lines and sometimes bump into each other. Gases don't keep a definite shape or volume. They always fill any container. Particles in gases have more energy than in solids or liquids. When particles bounce of walls in a container they create pressure. The particles are always moving randomly. The hotter the gas gets the faster they move.
• When substances change from one state to another, it is considered a physical change
• Heating and cooling substances can cause them to change state
• Example of state change: Solid to a liquid

  • Stage 1: When a solid is heated, its particles gain more energy
• • Solid to Liquid: Stage 2: This increased energy makes particles vibrate more, weakening the forces between particles and causing the solid to expand
• • Solid to Liquid: Stage 3: At a certain temperature, the particles have enough energy to break free from their positions, leading to melting and the solid turning into a liquid
• Liquid to a Gas:

  • Stage 4: When a liquid is heated, the particles gain even more energy, weakening and breaking the forces holding the liquid together
• • Liquid to Gas: Stage 5: At certain temperatures, the forces between particles break, and the liquid turns into a gas through evaporation
• In Chemical reactions, chemical bonds between atoms break and the atoms change places. The atoms you start off with (reactants) are rearranged to form different substances (products). Chemical changes are harder to undo than physical changes.
• A chemically pure substance is something that's made up of just one element or compound. If there's more than one in the substance then its not pure its just a mixture. Example: Fresh air is thought of as pure but its chemically impure. Its a mixture of gases such as nitrogen and oxygen.
• Every pure substance has a sharp melting point and boiling point. Sharp means that it will only melt or boil at a single temperature. e.g. pure ice melts at 0 degrees. And pure water boils and 100 degrees.
• Test for pure substances: Measure the melting point of the sample using melting point apparatus. This lets you heat up small samples of a solid very slowly, so you can find the exact temperature it melts at. If the melting point is the same as the expected melting point then the substance is pure. If its different, then its a mixture.
• How to use simple distillation to get pure water from sea water: Stage 1: Pour sea water into the distillation flask. Stage 2 Connect the bottom end of the condenser to a cold tap. And run cold water through the condenser to keep it cool. Stage 3: Heat the distillation flask slowly. The water will evaporate before the salt because it has a lower boiling point. Stage 5: The water vapour goes into the condenser. It cools and condenses. Stage 6: It flows into the beaker where its collected.
• Fractional distillation to separate a mixture of liquids:

  • Stage 1: Put the mixture in a flask and attach a fractionating column and condenser above the flask
  • Stage 2: Heat the flask slowly
  • Stage 3: The liquid with the lowest boiling point will evaporate first and reach the top of the column when the temperature on the thermometer reaches its boiling point
  • Stage 4: The evaporated liquid will condense and run down the condenser
  • Stage 5: The column is cooler nearer the top, so if liquids with higher boiling points evaporate, they will condense before reaching the top
  • Stage 6: When the first liquid is collected, increase the temperature until the next one evaporates
• Insoluble substance: Something that doesn't dissolve in another substance. E.g. sand is insoluble in water. To filter an insoluble solid from a liquid mixture you need to: Put some filter paper into a funnel. Pour your mixture into it. The liquid will run through the paper and the solid will get left behind.
• Crystallisation separates a soluble liquid from a solution: Stage 1: Pour solution into an evaporating dish. Stage 2: Gently heat the solution, the water will start to evaporate. Stage 3: Once crystals start to form stop heating it. Stage 4: leave solution to cool. Stage 5: Filter the crystals out of the solution and leave them in a warm place to dry.
• Chromatography: Draw a line near the bottom of a sheet of filter paper using a pencil. This is the baseline. Put a spot of mixture to be separated on the line. Pour a small amount of solvent into a beaker. Place the bottom of the paper into the solvent. Put a watch glass on top of the beaker to stop the solvent evaporating. The solvent will move up the paper. When the chemicals in the mixture dissolve in the solvent they will move up the paper.
• A chromatogram will have an R value. The equation is: R value = Distance travelled by solute divided by distance travelled by solvent.
• Water purification happens in 3 stages: 1: Filtration: A wire mesh stops large bits (e.g. twigs) going through. Then gravel and sand beds filter out any other solid bits. 2: Sedimentation: Chemicals are added which make smaller particles clump together and settle at the bottom. 3: Chlorination: Chlorine gas is bubbled through the water and kills harmful bacteria.