Chemistry IA help - no trends

[Vsu]

I'm doing my chemistry IA (SL) and my question is how temperature affects the buffer capacity of the citric acid - disodium hydrogen phosphate buffer (citrate-phosphate buffer).  

I've done the temperatures 10, 25, 40, 55, 70 degrees celsius, and I've done a number of trials for each (5+) and I've been looking at how many millilitres of NaOH it takes to break buffer capacity (so on a titration curve, the point when it starts to shoot up). The millilitres it takes for each of the temperatures all seem to be the same, so in conclusion, my data presents no trend in results. There also don't seem to be any literature values that I can find to compare this data to. I was wondering if it's alright to not have a trend and still be able to get a high mark. I've done a lot of processing of data, but I'm not sure if this will allow me to analyse it? Thank you.

My teacher sort of said it was fine but I'm still worried. There's also not a lot of information out there on this particular buffer, McIlvaine Buffer, only on how to make it. 

[ABKor752]

I had the same problem. My data had virtually no trend but my teacher said that if I could explain why this was the case with deep analysis, then I could show my scientific knowledge even without a clear trend. I wouldn't worry. Even if you don't have formal research or literature values, just explain the lack of a trend using what you know about the topic, and possibly explain mini-trends (i.e. an increase from one setting to another, followed by a more dramatic decrease, etc.)

[Vsu]

3 minutes ago, ABKor752 said:

I had the same problem. My data had virtually no trend but my teacher said that if I could explain why this was the case with deep analysis, then I could show my scientific knowledge even without a clear trend. I wouldn't worry. Even if you don't have formal research or literature values, just explain the lack of a trend using what you know about the topic, and possibly explain mini-trends (i.e. an increase from one setting to another, followed by a more dramatic decrease, etc.)

Thanks! This makes me feel a little more relieved.

Can I ask whether for your IA, did you know if you were meant to see some kind of a trend? Or if you went in really just to find out if there would be?
Also, what do you mean by mini-trends? 

Thank you so much!

[ABKor752]

My IA topic was enthalpy change of solution, which, although it does not focus on chemical processes between two "chemicals", my teacher said that if I explained it from a molecular perspective then it works. Now, enthalpy change of solution is a byproduct of lattice enthalpy and enthalpy of hydration. I was testing the enthalpy change of solution of transition metals going across the periodic table. The issue is that both lattice enthalpy and enthalpy of hydration generally increase in magnitude across the periodic table, so mathematically, the enthalpy change of solution balances out, resulting in no clear trend. I had not known this before, but I explained in my IA the trends of lattice enthalpy and enthalpy of hydration and I explained how this resulted in no trend. I spent months trying to find literature values but finally find them, and those had no trend, either.

By mini-trends, referring to my investigation, the resulting enthalpy change of solution literature values for my five salts (going across the periodic table) were -65, -64, -65, -31, -55, or something like that. I talked about why -31 was so different than the other values (this is a mini-trend because it doesn't encompass all the data into a single regression equation or something like that), and explained why it then jumped back down to -55.

I know that the pH of water changes, albeit only very slightly, with temperature, (between something like 6.8 and 7.2), but because its concentration of H+ and OH- are still equivalent, it is still considered neutral. In your titration curves, the center of the vertical line (equivalence point) is the pH, so a change in temperature may only have had a miniscule effect on the amount of NaOH needed to titrate a barely-changed-pH buffer solution. You could discuss how there might technically need to be a small increase/decrease in the amount of NaOH but because of random and systematic errors this is too negligible, thus resulting in a stagnant trend. That's the very basic science behind it and I probably got some facts wrong, but you get the idea. Talk about what should have happened, how that still results in a small trend, why this wasn't exactly seen in the experiment, etc.

Hope this helps!

 

[kw0573]

Chem IA is a not a math game of who can look for the trend that may or may not exist. I think best way out is to look at the equilibrium reaction of the buffer solution and how temperature affects that equilibrium. For example, you can use van't hoff equation to estimate the difference in equilibrium constants (and you may have to look up some literature values).