End of yr7 paper 2 science

• Dissolving


  Mixing a soluble solute into a solvent until it is fully incorporated to create a solution
• Solutes dissolve faster with

  • Increased temperature
  • Greater surface area
  • Stirring
• Soluble


  Able to be dissolved
• Solvent


  The substance that something dissolves in
• Solute


  The substance that is dissolved
• Solution


  A liquid containing a dissolved solid or another liquid
• Diffusion


  1. Particles flow and move about until they are evenly spread throughout

  2. Particles move from an area of high concentration to an area of low concentration
• Rate of diffusion is affected by

  • Concentration gradient
  • Temperature
• Diffusion rate


  Faster when concentration gradient is steep or solution is at higher temperature
• Filtration


  1. Solution is passed through a filter paper and a funnel

  2. Residue remains in the filter paper

  3. Filtrate is the part which passes through the filter
• Evaporation


  1. Solution is heated, the liquid evaporates and the solid crystallises

  2. If evaporation and crystallisation occur quickly, the crystals will be small

  3. If it occurs slowly, the crystals will be larger
• Distillation


  1. Water is heated and evaporates from the flask, flows upwards and into the condenser

  2. Condenser causes the water vapour to condense back into a liquid, which flows into the beaker
• Compounds contain two or more different elements chemically bonded together
• Mixtures contain substances that are not chemically bonded
• A pure element or compound contains only one substance, with no other substances mixed in
• Impure materials are mixtures of elements, compounds, or both
• Different types of mixtures

  • Gas-gas (air)
  • Liquid-liquid (solutions, e.g. beer)
  • Solid-solid (metal alloys)
  • Gas-liquid (aerosols and foams)
  • Liquid-solid (solutions, e.g. salt water)
  • Solid-solid (smoke)
• Separating Rock Salt


  1. Create a solution of the rock salt with water, only the salt will dissolve

  2. Filter the solution, the insoluble sand will collect as residue, the salt water solution will pass through

  3. Heat the salt water solution, evaporation or distillation can be used to collect the salt crystals or the water
• Chemical change


  New compounds or different elements are formed
• Physical change


  The substance simply changes physical state, e.g. solid to liquid, liquid to gas
• Chromatography


  1. Colours are separated because they have varying solubilities

  2. The separate inks are carried different distances up the stationary phase (filter paper) by the mobile phase (solvent)
• Potential Difference


  The amount of push energy provided by the battery to a moving charge
• Potential difference tells us how hard the battery 'pushes' the electrons around the circuit, the larger the potential difference the bigger the 'push'
• Potential difference


  Measured in volts (V) using a voltmeter, connected in parallel with the component
• Resistance


  The measure of how difficult it is for a flow of charge to pass through a component
• As resistance increases


  The less current will flow around the circuit
• As resistance decreases


  The more current will flow around the circuit
• Resistance


  Measured in ohms (Ω)
• Resistance


  Can be calculated using the equation: resistance = potential difference / current
• Independent variable


  The variable you change in an investigation to see how it affects the dependent variable
• Dependent variable


  The variable you measure or observe in an investigation
• Control variable


  A variable that could affect the dependent variable so must be kept the same
• Factors affecting resistance in a wire

  • Temperature
  • Width of wire
  • Length of wire
  • Type of material
• As temperature increases

  Resistance increases
• As width of wire increases

  Resistance decreases
• As length of wire increases

  Resistance increases
• Conductors


  Have low resistance so allow current to pass through easily
• Insulators


  Have high resistance so it is difficult for current to flow through them
• Atoms


  Made up of positive protons, negative electrons, and neutral neutrons
• Atoms contain an equal number of protons and electrons so have no overall charge