Short Intro: Hi, I've been assigned coursework for my A levels [16-18 year olds] where I've been told to start the theory part of my write up during my summer holidays
We are all investigating rates of reactions investigations and I've been assigned Mg and Acid. My basic aim is to find the rate equation and the activation enthalpy.
I'll be investigating the RoR by using Mg ribbon/powder + different concentrations of the acid and seeing how much gas is formed in X seconds [More gas formed = faster reaction]. Moreover, I will be using different concentrations of the acid and seeing the temp. rise in X seconds [higher temp. rise per time = faster reaction].
I will be finding out the activation enthalpy by seeing the effect of different temperatures on the rate. I will hope to do this by having the reaction take place in a water bath.
I have 3 questions:
1. Although I plan to use the above methods to measure the rate - they will have to be done manually [I don't think my school has electronic thermometers which can be connected to a data logger and I'd much prefer to have at least one method of data which is automatic]. On the help sheet I was given, it was suggested that I can use a different technique [explicitly suggesting conductivity and pH].
Will there be a change in pH when I do the reaction? From googling around [Google says that the acid is neutralised and a salt is made... how is it neutralised?] and it suggesting explicitly on the help page it seems that measuring a pH change is possible/measurable [I just want more of a confirmation really]
2. Will changing the temperature of the reaction via a water bath be a sensible approach to find the activation enthalpy? I know that the reaction is exothermic so obviously [or rather not] as the reaction carries out, the faster the reaction becomes due to the increase in temperature. But to be honest, it could be counted as only a drift in results as the temperature rise should theoretically be constant in each reaction (and hence its effect on the rate of reaction) for the same concentration. My gut feeling says that it's a perfectly fine method but I asked on another forum and they said:
"...it is very difficult to control for T in a particularly effective way."
and
"... a water bath will help, but I'd guess not too successfully."
I can't think of any large scientific reasoning behind why it would be hard to control the temp. for the reaction and why a water bath would not do it too successfully...
3. Possible comprehension confusion rather than direct chemistry confusion:
In my help sheet it says that a possible investigation would be to:
"Investigate the effect of other acids (including weak acids) on the rate of the reaction. You will be able to find the order of reaction for each acid and hence the rate equation for the reaction."
I initially got confused at this, asking myself "Why would getting the orders of multiple different acids help me find the rate equation?" But I understand now that it just means "Pick any acid, focus on it and find the rate equation for it" - am I right?
Many thanks (sorry for the wall of text!)