Chemistry mine

• Allotropes of Carbon
• Allotropes


  Different physical forms of the same element
• Carbon has quite a few allotropes with lots of different properties
• Diamond


  • Very hard
  • Doesn't conduct electricity because it lacks free electrons or ions
• Graphite


  • Contains sheets of hexagons
  • Covalent bonds between layers are weak, allowing layers to slide over each other, making graphite soft and slippery
  • Has high melting point due to strong covalent bonds within layers
  • Contains delocalised electrons that can conduct electricity and thermal energy
• Graphene


  • A sheet of carbon atoms joined in hexagons
  • Only one atom thick, making it two-dimensional
  • Network of covalent bonds makes it very strong and light
  • Contains delocalised electrons that can conduct electricity
• Diamond, graphite and graphene contain exactly the same atoms, the difference in properties is due to the way the atoms are held together
• Nanoparticles


  Tiny particles with a huge surface area to volume ratio
• The effects of nanoparticles on health aren't fully understood
• Some people believe products containing nanoscale particles should be clearly labelled so consumers can choose whether to use them
• Nanoparticles used in sunscreens may get into the body and potentially damage cells, and when washed away may damage the environment
• Mole


  Unit used to measure the amount of a substance
• Finding the number of moles in a given mass


  1. Mass in g (of an element or compound)

  2. Divide by molar mass (M)
• Formula triangle


  Can be used to find mass, number of moles or molar mass if the other two are known
• In a chemical reaction, mass is always conserved
• No atoms are destroyed or created during a chemical reaction
• The total molar mass of reactants equals the total molar mass of products in a balanced reaction
• Concentration


  Measure of how crowded solute particles are in a solution
• Calculating concentration in g/dm³

  Mass of solute / Volume of solution
• Calculating concentration in mol/dm³

  Number of moles of solute / Volume of solution
• Atom economy


  Percentage of reactant atoms that end up in the desired product
• Calculating atom economy


  Relative formula mass of desired product / Relative formula mass of all reactants x 100
• Percentage yield


  Actual mass of product made / Maximum theoretical mass of product x 100
• Percentage yield is always between 0-100%
• Titrations


  A method of analysing the concentrations of solutions
• Titrations


  • They're pretty important
  • Used to find out concentrations
  • Allow you to find out exactly what volume of acid is needed to neutralise a measured volume of alkali-or vice versa
  • You can then use this data to work out the concentration of the acid or alkali
• How to do a titration

  1. Add a set volume of the alkali to a conical flask using a pipette and pipette filler

  2. Add two or three drops of indicator

  3. Use a funnel to fit a burette with some acid of known concentration, making sure to do this BELOW EYE LEVEL

  4. Record the initial volume of the acid in the burette

  5. Use the burette to add the acid to the alkali a bit at a time, giving the conical flask a regular swirl, going especially slowly when the end-point colour change is about to be reached

  6. The indicator changes colour when all the alkali has been neutralised

  7. Record the final volume of acid in the burette, and use it, along with the initial reading, to calculate the volume of acid used to neutralise the alkali
• Pipette


  Measures only one volume of solution, fill to about 3 cm above the line then drop down carefully to the line
• Burette


  Measures different volumes and lets you add the solution drop by drop, the scale down the side shows the volume of acid used
• You should repeat titrations and find a mean volume to increase the accuracy and spot any anomalies
• The first titration should be a rough one to get an approximate idea of where the solution changes colour at the end-point
• You then need to repeat the whole thing a few times, making sure you get pretty much the same answer each time within 0.10 cm
• Finally, calculate a mean of your results, ignoring any anomalous ones
• Universal indicator


  Used to estimate the pH of a solution, it can turn a variety of colours, each indicating a narrow range of pH values
• During a titration between an alkali and an acid, you want to see a sudden colour change at the end-point, so you need to use a single indicator
• Single indicators for titrations

  • Phenolphthalein (colourless in acids, pink in alkalis)
  • Litmus (red in acids, blue in alkalis)
  • Methyl orange (red in acids, yellow in alkalis)
• When doing a titration, you need to go slowly as you reach the end-point, and do repeats to find a mean, to ensure accuracy
• chlorine - damp limitus paper - bleaches white
• Carbon dioxide - limewater - turns cloudy
• Hydrogen - lighted splint - squeaky pop