Topic three- Chemistry

Topic three- Chemistry

1. Flame tests.

   • potassium ---> purple
   • lithium ----> pinky red
   • Calcium ----> orangey-red
   • sodium ----> yellowy - orange
   • Barium -----> green
   • Flame tests are used to find out cation metals.
     • pawwwsitive ( positive ions)

2. Precipitation reactions

   • precipitation reactions are used to find out anions.
     • negative ions
   • precipitation reactions can also be used to test for cations
     • Aluminium (3+) and Calcium (2+) create a white precipitate.
     • copper (2+) precipitates out blue
     • iron (2+) creates a green precipitate
       • Iron ( 3+) creates a brown precipitate
     • To test these transition metals we added sodium hydroxide

3. TITRATIONS

   • A strong acid added to a strong alkali = a base and a salt. But ONLY if it's in the right quantities.
   • 1) fill the BURETTE with HCL solution to exactly zero. Use the tap to pour some out if it's not exact.
     • 2) Fill the beaker underneath the burette with 25cm cubed of NaOH.
       • Put two drops of phenolphthalein indicator into the beaker.
         • Let the HCL into the beaker until the colour makes a slight change and then turn the tap one turn at a time.
           • Make sure you're swirling the beaker all the time and when the product turns colourless stop letting the HCL out.
             • wash the conical flask with dilute water and the acid that you're using and refill it with alkali and the indicator.
               • redo the experiment and record the results on the table.
       • place a while tile under the beaker

4. Calculating moles

   • mass = moles * formula or atomic mass
   • moles = volume * concentration
     • Step 1) write the known information
       • what's the concentration, the volume etc.?
     • Step 2) write out the balanced equations
     • Step 3) Calculate the moles
       • concentration = moles * volume
     • divide cm by 1000 to create dm
       • dont actually understand this :S

5. Hard water

   • permanent
     • contains calcium hydrogen carbonate ions and magnesium hydrogen carbonate ions
     • ion exchange resin columns
       • The resin is coated in sodium ions, which have a positive charge. The magnesium and calcium have a stronger positive charge and so displace the sodium ions. The sodium ions dissolve into the water- this hard water is softened using this method.
     • washing powder
       • creates a scum and removes the calcium and magnesium ions.
   • temporary
     • can be boiled to soften. Creates CaCo3 (s) which is limescale.

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