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Hi All, 

 

So, I've been recently working on a prac involving how the rate of reaction (between Magnesium and Hydrochloric acid) can be affected by increasing surface area of the Mg ribbon. 

 

And, whilst I don't have any issues discussing the prac itself and the results it produced, I haven't been able to find any literature values at all. I've really tried looking everywhere, and I've only gotten as far as finding a website which showed me some values for varying HCl concentration, not Mg surface area (by cutting up the ribbon into different pieces). And as much as I'd like to, I can't base my prac on varying concentration, since that was the other prac that I did that I'm planning on submitting to IB. 

 

If anyone has any ideas, it'd be much appreciated--- 

 

I'm perhaps slightly panicking about this (our teacher only gave us a few days to complete the entire practical report), so....yeah, a prompt reply would be extremely extremely appreciated!

 

Thank you!!!!!!

 

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I don't think you will need literature values if you form a valid hypothesis. For instance, if I did a kinetics lab on Mg and HCl, I can deduce from the stoichiometric coefficients that HCl will be consumed twice as quickly as Mg. Then, the accuracy of my results can be compared to my hypothesis (order of rxn with respect to HCl is 2). If you have literature values, then accuracy of the results can be compared directly with the existing data. 

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I don't think you will need literature values if you form a valid hypothesis. For instance, if I did a kinetics lab on Mg and HCl, I can deduce from the stoichiometric coefficients that HCl will be consumed twice as quickly as Mg. Then, the accuracy of my results can be compared to my hypothesis (order of rxn with respect to HCl is 2). If you have literature values, then accuracy of the results can be compared directly with the existing data. 

 

Okay... though doesn't the IB specify that you need to include literature values for the pracs that you perform? 

 

Also, just another question: If I were to not use literature values and just deduce the accuracy of my results from calculation, would that mean that in my prac, the data that I collect should be enough for me to calculate the rate expression? Because if so, doesn't that mean that I would have to also alter the concentrations of both Mg and HCl to determine the rate expression? And consequently, wouldn't that mean that I've essentially been working with three independent variables? 

 

The thing is, my practical is regarding rates of reaction, not deducing the rate expression. I can understand that essentially, the rate of reaction is determined by the rate expression, however I'm not sure whether I would be able to do the rate expression, since it would involve two processes:

1) Changing Mg concentration whilst keeping HCl concentration constant

2) Changing HCl concentration whilst keeping Mg concentration constant

 

And from what I know, this process in itself would involve working with two independent variables (respective concentrations of either reactant) and not the one independent variable that IB wants to see in Pracs.. 

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1. I don't know, does the IB specify that you need literature values? I have never seen it as a requirement on a rubric before (although I have seen "When appropriate, literature values are compared", which implies that they are optional). Maybe you should ask a teacher for verification, but as long as you discuss the accuracy and precision of your experiment in the conclusion, I don't think you will need literature values.

2. If you quantitatively deduced that e.g. as surface area is doubled, rate of rxn is doubled, then you wouldn't need a rate expression. My personal example was a lab that I remembered doing, and it was irrelevant to your problem.

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