Question

Why is there an excess of thiocyanate added to solutions 1-5 in part I of the experiment? Select all that apply.

a) To enhance color
b) To increase solubility
c) To inhibit a specific reaction
d) To maintain pH stability

Answer 1

Excess thiocyanate is added in the experiment primarily to enhance the color of the Fe(SCN)²⁺ complex for better visibility and to drive the reaction equilibrium forward, favoring the formation of the measurable complex. It serves no role in increasing solubility, maintaining pH stability, or inhibiting specific reactions in this context.

Step-by-step explanation:

There is an excess of thiocyanate added to solutions 1-5 in part I of the experiment for several reasons. An important reason is that it serves to enhance the color of the reaction mixture. Specifically, thiocyanate forms a soluble red-colored complex with Fe³⁺, known as Fe(SCN)²⁺, which is visually detectable, aiding in the qualitative analysis of the reaction.

Secondly, adding excess thiocyanate shifts the equilibrium according to Le Chatelier's principle. When excess SCN⁺ is added, it drives the reaction forward, favoring the formation of the red-colored Fe(SCN)²⁺ complex. This helps ensure that the reaction proceeds to a sufficient extent that can be measured or observed.

Lastly, excess reagent can act to inhibit a specific reaction by tying up the reactants in a complex, preventing side reactions. This is not one of the main reasons in this particular experiment but can be applicable in other scenarios involving thiocyanate.