2.36 describe tests for the cations: i Li+, Na+, K+ Ca2+, using flame tests ii NH4+, using sodium hydroxide solution and identifying the ammonia evolved iii Cu2+, Fe2+ and Fe3+, using sodium hydroxide solution

2.36 •testing for metal cations with flame  

      

        •lithium, burns red 

        •sodium, burns yellow 

        •potassium, burns lilac 

        •calcium, burns red 

        •1. use a platinum wire loop, dipping it in dilute HCL

        •2. once it burns colourless, dip it in the sample, and put it back in the flame 

     

        •testing for ammonium ions 

        •1. add sodium hydroxide to ammonium ions 

        •2. use a damp piece of red litmus paper, which will turn blue if ammonia is present 

                  •the smell is also pungent 

        •ammonium chloride + sodium hydroxide —> ammonia + sodium chloride + water 

                                  •NH4Cl(aq) + NaOH(aq) —> NH3(g) + NaCl(aq) + H2O(l)

        •ionic equation: NH4(+)(aq) + OH- —> NH3(g) + H2O

                  •ammonium ions from the solution being tested, by testing ammonia 

                  •hydroxide ions from the sodium hydroxide added 

       •testing for metal ions 

       •many metal hydroxides are insoluble and precipitate out of solution when formed

        •1. add sodium hydroxide 

        •2. if you get a coloured insoluble hydroxide, you can tell which metal was in the compound

        •copper (II), Cu(2+), blue precipitate           Cu(2+)(aq) + 2OH-(aq) —> Cu(OH)2(s)

        •iron (II), Fe(2+), green precipitate              Fe(2+)(aq) + 2OH-(aq) —> Fe(OH)2(s)

        •iron (III), Fe(3+), brown precipitate            Fe(3+)(aq) + 3OH-(aq) —> Fe(OH)3(s)

        •copper (II) sulphate + sodium hydroxide —> copper (II) hydroxide + sodium sulphate

                               •CuSO4(aq) + 2NaOH(aq) —> Cu(OH)2(s) + Na2SO4(aq) 

        

        •ionic equation: Cu(2+)(aq) + 2OH(-)(aq) —> Cu(OH)2(s)