[happystarlight]

My aim is to find out how much water (at 100 degrees) will dissolve 5g, 10g, 15g...25g of Potassium Nitrate (KNO3).
This is approximately: 2ml, 4ml, 6ml, 8ml, 10 ml of water respectively.

So I've graphed the mass of potassium nitrate (x axis) against the amount of water needed to dissolve it (y-axis), and I have a linear trendline.

I am now trying to find out how much potassium nitrate will dissolve in 100 mL of water.
My teacher has told me that I need to find the gradient of the inverse of this trendline - that will be the amount of potassium nitrate able to be dissolved. But I'm not sure why I need to do that. Can't I just substitute 100 mL for 'y' in the equation of the trendline? Then I have my x-value, right?
Apparently, I shouldn't do this, but I don't understand why I need to find the gradient of the inverse equation.
Anyhow, I did this, and I got 1/0.4050 which is approximately 2.47 g (shouldn't it be at least 247 g?)

Also, when I work out the inverse of the equation of the trendline, how do I calculate the uncertainties of this???

Now I am extremely confused, and I have no idea how to do my lab report.
(My teacher is on vacation right now, and isn't answering his emails until he gets back from vacation, and that's when the lab report is due!!)

Thanks so much for helping!

[fledarmus]

What is the mathematical definition of the gradient? Pay particular attention to the units...

[Arkcon]

Look over here:  http://www.chemicalforums.com/index.php?topic=47796.0  Someone else on these boards asked a similar (but not exactly the same) question.  But ... they have a graph.  See if it helps you visualize the questions better.

[happystarlight]

What is the mathematical definition of the gradient? Pay particular attention to the units...

The gradient is change over the points... I'm not sure what you're trying to say about the units though, sorry.

I'm really not sure why I need to find the gradient of the inverse though....


Also, To Arkcon: I looked at the link, but it's not really relevant to my experiment. Thanks anyway.

[fledarmus]

What units is the change in? What units are the points in? What would be the units of the gradient?