Chemicals and Observations

• Chemical formula


  Symbols used to talk about chemicals
• Chemical formula for an element

  • Only one capital letter
• Chemical formula


  Gives information about the type and number of each atom present in a compound
• Naming chemicals


  • Element names are listed on the periodic table
  • Some compounds have odd names which you just need to learn
• Naming compounds containing 1 metal and 1 non-metal

  1. Find and write the name of the metal

  2. Find and write the name of the non-metal

  3. Change the end of the name of the non-metal to -ide
• Compounds containing 1 metal and 1 non-metal

  • FeS = Iron sulfide
  • TiC = Titanium carbide
  • Al2O3= Aluminium oxide
• Naming compounds containing 1 metal and 2 non-metals

  1. Find and write the name of the metal

  2. Find and write the name of the non-metal that isn't oxygen

  3. Change the end of the name of the non-metal to -ate to show that the compound contains oxygen
• Compounds containing 1 metal and 2 non-metals

  • GaPO4 = Gallium phosphate
  • Al2(CO3)3 = Aluminium carbonate
  • MgSO4 = Magnesium sulphate
• Element formulae


  • For most elements, their chemical formula is their symbol from the periodic table
  • Eight elements exist as diatomic molecules, their formula has a subscript '2'

  
• Diatomic elements


  • Can be learned from their shape on the periodic table
• Good observations to make when describing substances

  • Solid, liquid or gas?
  • Coloured or colourless?
  • Crystalline or powdered? (for solids)
  • Clear or cloudy? (for liquids)
• Good observations to make when describing changes

  • Is there any fizzing?
  • Has a solid appeared or disappeared?
  • Has anything changed colour?
  • Are there any unusual sounds or smells?
• pH scale


  • Used to describe how acidic or alkaline a solution is
  • pH < 7 is acidic
  • pH = 7 is neutral
  • pH > 7 is alkaline

  
• Indicators


  Substances that change colour to tell you about the pH of a solution
• Indicators with two colours

  • Methyl Orange: Acidic = Red, Neutral = Yellow, Alkaline = Yellow
  • Phenolphthalein: Acidic = Colourless, Neutral = Colourless, Alkaline = Pink
• Using indicators to find if a substance has been neutralised

  1. Adding acid to alkali in methyl orange - yellow to orange

  2. Adding alkali to acid in methyl orange - red to orange

  3. Adding acid to alkali in phenolphthalein - pink to colourless

  4. Adding alkali to acid in phenolphthalein - colourless to pale pink
• Litmus paper


  Can start as either red or blue, look at how the colour changes
• Universal indicator


  Range of colours tells you the approximate pH
• Universal indicator has lots of colours and so it is difficult to see if a substance has been neutralised