Combustion of alkanols (1 Viewer)

[undalay]

For the molar heat of combustino for alkanols.

Do we need a line of best fit for the graph? or is it enough just to join the dots?
Do we even need to join the dots?


Does the line of best fit always need to pass through 0,0 ( i was told be some student teacher we do ages ago :/)
Does the line of best fit need atleast 3 points lying on it ( also told me this)
<!-- / message -->

 

[namburger]

Does the line of best fit need atleast 3 points lying on it
<!-- / message -->

You need at least 2 pts for a line and when there are 2 points you can just connect the points. With 3, one line may not be enough to connect the points so the line of best fit is needed for at least 3 pts.

As for your other q's, depending on your graph
Like if the x-axis is the molar mass of the alkanol than a line of best fit is needed so we can see the general trend as molecular mass increases, what happens to the molar heat of combustion.
But if the x-axis is the name of the alkanol, than you can do a column graph =D

Line of best fit DOES NOT have to pass through origin

 

[Lucid Scintilla]

You oughtn't ever join the dots. With this third-column dot point (yes?) - which I'll assume you, undalay (Fort Street, IIRC), did a prac about - I was required to carry out the procedure to find empirical data, plot it, and explain the trend (linear, increasing changes in enthalpy (and molar heats), due to homologous family and the obvious increase in the number of molecules (increased bonds, increased energy released when broken)).

This is "identify data sources, choose resources and perform a first-hand investigation to determine and compare heats of combustion of at least three liquid alkanols per gram and per mole", right?

Does the line of best fit always need to pass through 0,0 ( i was told be some student teacher we do ages ago :/)

No, it doesn't always need to; in fact, one pretty much never forces it through the origin (unless specifically stated otherwise).

Does the line of best fit need atleast 3 points lying on it ( also told me this)

Well...
1's not enough. It's a point.
2's not enough. Who or what's to say either one is accurate? Awful reliability.
3's ... not enough. Same as above.
4's ... better.
5's ideal.
As a sidenote, there's no rule (unless specified in the question) regarding whether you should force the line through the first and last point (this is assuming that they're all empirical measurements).

http://img228.imageshack.us/img228/328/20080406230818mj6.jpg

As for your other q's, depending on your graph
Like if the x-axis is the molar mass of the alkanol than a line of best fit is needed so we can see the general trend as molecular mass increases, what happens to the molar heat of combustion.
But if the x-axis is the name of the alkanol, than you can do a column graph =D

Yup.

Chances are, though, that this will require one to draw up a scatterplot. =p

 

[samwell]

You need at least 2 pts for a line and when there are 2 points you can just connect the points. With 3, one line may not be enough to connect the points so the line of best fit is needed for at least 3 pts.

As for your other q's, depending on your graph
Like if the x-axis is the molar mass of the alkanol than a line of best fit is needed so we can see the general trend as molecular mass increases, what happens to the molar heat of combustion.
But if the x-axis is the name of the alkanol, than you can do a column graph =D

Line of best fit DOES NOT have to pass through origin

always do a line of best fit in any scientific graph. I once made the mistake o drawing a LOBF and a join the dots to compare the values that is like the worst thing u could ever do. Lines dont have to pass through 0,0.