# jenicalina

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Nov 2014
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1. ## Calculating rates of reaction

Hi all, So I've recently been trying to calculate the rates of reaction, but I've been slightly confused as to how I should go about it. Should I use this equation: rate of reaction = 1 / t (t is time in minutes) OR rate of reaction = concentration of reactant / time taken for reaction to occur Thanks in advance!
2. ## IA Help Please! Iodine Clock

I know when you perform a classic iodine clock reaction, the reacting solution is meant to turn blue-black. However, when I performed it... not only did it not turn blue black, but instead--- brown?! In my experiment, I added two different solutions: Solution 1 contained: 20mL of a reacting solution (1.5g of KI added to 1.9g of Na2S2O3 in 250cm3 of water) 10mL sulfuric acid (H2SO4) 2mL of dilute starch solution Solution 2 contained: Distilled water Variable volumes of hydrogen peroxide (H2O2) Did I do something wrong? I've processed the data that I've collected, and my trends are looking fine, however I just don't know why my solution turned brown-black instead of blue-brown, nevertheless explain this in my conclusion. If it helps, the reaction did smell.... Could it be that the reaction that I did wasn't really an iodine clock at all..? Any help or suggestions would be greatly appreciated!!
3. ## Lab Report Literature Values

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..
4. ## Lab Report Literature Values

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!!!!!!
5. ## SL Japanese or Ab Initio Spanish

As a person who was faced with exactly the same decision, I think that personally, it would be better to take up Japanese SL instead of ab initio Spanish. One of the things that our coordinator told us was that whilst ab initio Spanish initially seems easy, it's actually just as hard as taking up any other Language SL, as the speed at which they learn the language will just progressively speed up over the course of the two years. Essentially, my co-ordinator told me that by the end of the two years, your fluency in Spanish (if you are taking ab initio) will be of the same level as if you were taking Japanese SL instead. Whilst you do mention that the years you spent learning Japanese were mediocre, I don't necessarily think that it should therefore immediately become a point for you to completely drop it. After all, even if you didn't learn anything in the first 4 years, at least you've been exposed to the Japanese language (noting that exposure to languages is extremely vital if you are to do well). To be fair, I didn't even study for any of my Japanese exams prior to entering the IB course, and I've still chosen Japanese SL. Also, I've been doing the Japanese SL course, and honestly, it's not as bad as it seems. You just need to show some commitment and dedication to your language studies - just like you would for all your other subjects if you intend to get a 7.

Hi all, I'm not quite sure why the enthalpies of combustion for a secondary alcohol is lower than a primary alcohol- does anyone else have any ideas? From my textbook, the only thing it mentions is that the position of the functional group can greatly influence reactivity, but it doesn't really specify how. The only thing it does explain is that an increasing carbon chain can lead to higher enthalpies of combustion (more bonds to break), but that doesn't explain the difference in enthalpies between a secondary alcohol and a primary alcohol. Please help!
7. ## Chemistry HL/SL help

Hi all, Since this is a Chemistry HL/SL help discussion, I was hoping somebody would be able to answer this question for me: Why does the secondary alcohol have a lower heat/enthalpy of combustion as opposed to a primary alcohol? The textbook I've got never talks about the reasons why; it only tells me that as the carbon chain gets larger, the enthalpies of combustion should increase because you need to break more bonds. But secondary and primary alcohols aren't necessarily going to be of different carbon chain lengths- for example, 1-propanol and 2-propanol, but their enthalpies of combustion are still different. Is it to do with the position of the function group (OH)? And if so, how does the position of the functional group affect the enthalpies of combustion? Please help! (>_<)
8. ## Lab Report Literature Values for Enthalpies of Combustion

Hi all, Does anyone know of a good source/database that has literature values on the enthalpies of combustion for 1-butanol and 2-butanol? I know that the data book has the value for 1-butanol, but there's no 2-butanol, and I've been looking everywhere on the net without much luck. Once I did find a pdf that had both, but I don't think it's very reputable, since it said that the enthalpy of combustion for 1-butanol is -639.3kJ/mol....whilst the IB data booklet has it at -2676kJ/mol. Any help is greatly appreciated in advance!
9. ## Lab Report Literature Values in IA's

Okay, I'll try that then! Thank you so much for your help! And yes, I actually haven't done a lot of IA's, this would be my second complete IA for Chem, in which for the first, we all have literally no idea what we were supposed to include. All the best with your incoming exams!
10. ## Lab Report Literature Values in IA's

Okay, well that definitely makes life a lot better in terms of writing up this IA- however, just another question: what should I do with the calculations on percentage error? I understand that with % error, you need the literature value in order to calculate it, and that it's also important because then with the % error you could then talk about the accuracy of your data in the IA. But if there's no such literature value to work off, then there's no method to calculate % error and therefore no way to talk about accuracy.... or is there another method/calculation I can use that still will indicate the accuracy of my results? I know so far that with standard deviation, I can write about data variability, and with standard error, if the error bars aren't overlapping, I can mention that they are likely to be statistically significantly different. (though I know that in Chemistry IAs, there's no need to include error bars in our processed data graphs: that's only for biology and physics) And also, just with some other questions: how long are our IAs generally supposed to be? I know that there isn't any word limit, but I had a friend of mine go up to 6,000 words... whilst mine remained at a sad 2,000. My general (and very basic) outline for IAs is that I should have at least 1 page for my conclusion, 1+ pages for my Evaluation. I'm not quite sure how much background information I should provide, because in my opinion, I don't think it's a major focus in the IA, so generally background information falls to just under half a page or so. In terms of processed data, I've also found myself sticking to making just one processed data table, and one graph. Should I be adding more into my IAs?
11. ## Lab Report Literature Values in IA's

Okay, I apologise in advance for creating this post which I'm sure has already been asked many times, but is there any particular resource or search term we can use to find the literature values for a Practical? I've been trying to search for the literature value of the time taken for the complete reaction of sodium thiosulfate (Na2S2O3) and hydrochloric acid (HCl) but with no luck whatsoever. As my practical's aim is to determine how the concentration of Na2S2O3 affects the rate of reaction, do I really need to find this literature value to compare with my data? I do understand its importance in the calculation of percentage error, however I'm also slightly confused as to how I would be able to calculate the % error if the literature value is for the complete reaction, and my intervals do not all result in the complete reaction (ie. there are limiting reagents due to concentration etc.) Many thanks-- P.S.: As my teacher wants me to submit this in less than a weeks time, I'd greatly appreciate if any type of suggestions can be provided as soon as possible.
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