Suggestions for an equilibrium demonstration

[richievuong]

I just got assigned a project on equilibrium. We have to demonstrate how factors can cause shifts in equilibrium. I got assigned common ion, so I have to show how the common ion effect can affect the equilibrium.

On Monday we can prepare the chemicals and practice doing the lab once before presenting our project on Wednesday.

Anyone have suggestions of good demonstrations/experiments that I can do and fit under the above criteria?

I googled up this:
http://quiz2.chem.arizona.edu/preproom/Demo Files/lead_chloride_solubility.htm

It seems like a viable plan but I'm not sure if my school has the chemicals... so if you suggest anything please make sure they are chemicals that are rather easy to obtain or is accessible in a high school environment

thanks

 

[Nino MMP]

!A common ion experiment that is easy to do in a high school environment is to add an acid/base (such as hydrochloric acid) to a buffer. A buffer is a solution of a weak acid and its conjugate base, or a weak base and its conjugate acid, which resists changes in pH when small amounts of acid or base are added to it. When the acid or base is added, the equilibrium of the buffer will shift, demonstrating the common ion effect. You can prepare a buffer using acetic acid and sodium acetate, for example.

 

[Blueshift5]

There are many different ways to demonstrate the common ion effect in an equilibrium system. One simple experiment you could try is mixing a solution of silver nitrate and a solution of potassium chloride. These two solutions will react to form a precipitate of silver chloride. However, if you add a small amount of sodium chloride to the silver nitrate solution before mixing it with the potassium chloride solution, the amount of precipitate formed will decrease. This is because the addition of the sodium chloride introduces a common ion (chloride ion) to the solution, which will shift the equilibrium towards the reactants and decrease the amount of precipitate formed.

Another experiment you could try is the reaction between iron(III) chloride and thiocyanate ions. When these two substances are mixed, they form a deep red color due to the formation of iron(III) thiocyanate complex ions. However, if you add a solution of iron(III) nitrate to the mixture, the color will become less intense. This is because the addition of the iron(III) nitrate introduces a common ion (iron(III) ion) to the solution, which will shift the equilibrium towards the reactants and decrease the formation of the complex ions.

It's important to remember that the common ion effect is not limited to just these two reactions. You can also explore the effect in other systems such as weak acid and base equilibria or in solubility equilibria. Just make sure to choose a system that is safe and accessible for high school students.

When conducting your experiments, make sure to vary the amount of common ion added and observe the changes in the equilibrium position. You can also try to predict the direction of the shift in equilibrium before adding the common ion and then compare your results to your predictions.

Overall, the key to a successful equilibrium demonstration is to choose a system that is easy to observe and understand, safe to handle, and allows for the manipulation of the equilibrium position through the addition of a common ion. Good luck with your project!