The reagent added is NaOH, observation is it turns litmus blue. The lab report wants the equation.
Litmus changes color with pH, no matter what cations/anions are present in the solution. It is just an acid/base equilibrium - you change protonated form into a non protonated one and they have different colors. Writing reaction equation is tricky, as litmus is a mixture of dyes. They share ta common chromophore though.
Next HCl is added and a white PPT forms.
Equation would be Ag+(aq)+Cl-(aq)=AgCl(s) the white PPT.
There are several cations that can get precipitated with Cl
-. Ag
+ is the best known one.
Then NH4-, and NH3 are added and a dark PPT is formed this would be Fe3+(aq)+3NH3(aq)=Fe(OH)3(s)+3NH4-(aq)
Something is off here. It Fe
3+ were present it would precipitate much earlier, after NaOH addition. Actually NaOH addition would also already precipitate AgOH.
Your reaction equation is wrong - it is not balanced, there is no such thing as NH
4-. You are right about Fe
3+/Fe(OH)
3. Probably best approach is to treat ammonia solution as if it was just a base.
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