Practical investigations
Read our general notes on Risk Assessment
I am trying to understand the relationship between activation energies of strong and weak acids when they react with metals. Why do strong acids have lower activation energies than weak acids?
Corrie writes....
Let's think about what is in solution and reacting with the metal on its surface. Strong acids will be completely dissociated in dilute solution, so the reaction is essentially between H+(aq) ions and the metal surface.
For weak acids the main species in solution will be the undissociated acid molecules. As the temperature is changed, the degree of dissociation will change. So the concentration of free H+(aq) ions will change. Things are getting complicated!
Basically the question is: with weak acids does the reaction proceed via H+(aq) ions and the metal only, or via acid molecules, or both? The fact that the activation energy seems to be higher for weak acids suggests one or other of the latter two possibilities. If most or all of the reaction is between molecules of the acid and the metal, an extra covalent bond (O-H) will need to be broken, which could explain the higher activation energy.
This is about all you can say at this level - the situation is obviously quite complex and more experiments would be needed to clarify exactly what's going on - which is not possible in an A-level investigation. The best you can do is to make some sensible comments about the possible alternatives and the effect they might be expected to have on the activation energy.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
back to Practical investigations
Rate this page or react
Share your views on this page, 0 ratings so far
updated: 18 December 2007
