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Capa

Chemistry: please help

Hi

I am doing a design experiment and I have so far decided to investigate the enthalpy change of combustion for ketones

However, to be able to do this I need to know the theoretical value and I have no idea how to find it.

Does anyone have an idea of what I could do and does the experiment look appropriate?

I would be very thankful for any answers

Capa...

Edited by Capa

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However, to be able to do this I need to know the theoretical value and I have no idea how to find it.

Check the data booklet. It has values for some carboxylic acids.

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Quick question: In a chemistry lab, do you propagate the uncertainty and do the normal calculations in one single step (e.g: (5 +/-0.1) + (4 +/0.1) = 9 +/-0.2) ? Or is it better to separate and propagate the uncertainty in another step?

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Quick question: In a chemistry lab, do you propagate the uncertainty and do the normal calculations in one single step (e.g: (5 +/-0.1) + (4 +/0.1) = 9 +/-0.2) ? Or is it better to separate and propagate the uncertainty in another step?

When adding (or subtracting) numbers, you add the uncertainties. So 5±0.1 + 4±0.1 = 9±0.2

To find the percent uncertainty, you would divide the uncertainty by the value and multiply by 100. So (0.2/9)*100

Hope this helps :rofl:

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I meant, do we have to explain how we calculated the uncertainty or can we just plug it in without explaining in details?

For example, do we present our work like this: 5±0.1 + 4±0.1 = 9±0.2 OR like this: 5+4=9 and 0.1+0.1= 0.2, therefore the answer is 9±0.2 (this is just a simple example it gets more complicated when we multiply or divide)

I hope u got what I mean. Thanks :rofl:

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I meant, do we have to explain how we calculated the uncertainty or can we just plug it in without explaining in details?

For example, do we present our work like this: 5±0.1 + 4±0.1 = 9±0.2 OR like this: 5+4=9 and 0.1+0.1= 0.2, therefore the answer is 9±0.2 (this is just a simple example it gets more complicated when we multiply or divide)

I hope u got what I mean. Thanks :rofl:

I do the first way, and this far my teacher hasn't complained.

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I meant, do we have to explain how we calculated the uncertainty or can we just plug it in without explaining in details?

For example, do we present our work like this: 5±0.1 + 4±0.1 = 9±0.2 OR like this: 5+4=9 and 0.1+0.1= 0.2, therefore the answer is 9±0.2 (this is just a simple example it gets more complicated when we multiply or divide)

I hope u got what I mean. Thanks

Personally, I would not allow a chance for the examinor to mark me down if he/she happens to see mine. It doesnt take that long anyways.

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I did mine the first way but I'm going to ask my teacher tomorrow just in case! Anw, thanks for the answers!

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Hi

I am doing a design experiment and I have so far decided to investigate the enthalpy change of combustion for ketones

However, to be able to do this I need to know the theoretical value and I have no idea how to find it.

Does anyone have an idea of what I could do and does the experiment look appropriate?

I would be very thankful for any answers

Capa...

I love it how the discussion went completely off topic...

Capa, here's something that might be helpful: Combustion of Ketones

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Haha, tahnk you very much ezex.... and yeah, I haven't replied before this cause I stopped looking at this thread went it went faaaaar off :D

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