Answer : The complete question is attached in the answer.
Answer 1) : To show the chemical equilibria between Fe and SCN to form a complex FeSCN. We can write the reaction as follows :
[tex] Fe^{+3}_{(aq.)} + SCN ^{-}_{(aq.)} <----> FeSCN^{+2}_{(aq.)} [/tex]
The Ferric ion when combined with thiocyanide forms a ion (iii) thiocyanate complex.
Answer 2) : To find the chemical equilibrium between Nickel and ammonia to form nickel-ammonium complex. The reaction is as follows:
[tex] Ni(OH_{2})_{(s)} + 6 NH_{3}_{(aq.)} <----> [Ni(NH_{3})_{6}]^{+2}_{(aq.) [/tex]
Here, the nickel reacts in solid state with 6 moles of ammonia and forms a nickel-ammonium complex.
Answer 3) : To show the colour change using phenolphthalein indicator with pH we can use HIn and In to show the relationship of chemical equilibrium.
[tex] HIn (clear) + H_{2}O <----> H_{3}O^{+} + In^{-} (pink) [/tex]
when phenolphthalein is added as an indicator in titration it forms a clear complex and when it reacts with water it forms hydronium ion and the indicator is left alone which gives pink colour as the end point.
Answer 4) : When calcium hydroxide undergoes dissolution or formation happens the chemical equilibrium can be shown as follows:
[tex] Ca(OH_{2}) <----> Ca^{+2}_{(aq.)} + 2OH^{-}_{(aq.)} [/tex]
Calcium hydroxide when dissolved in water forms calcium ions and hydroxyl ions are liberated in water.
Answer 5) To show the chemical equilibrium between cobalt and chloride forming cobalt chloride is as follows:
[tex] [Co(H_{2}O)_{6} ]^{+2} + 4Cl^{-} <----> CoCl_{6}^{-2} + 6 H_{2}O [/tex]
Here, in this reaction the cobalt hydorxide complex when comes in contact with chloride ions forms cobalt-chloride complex along with 6 moles of water.
