How do you calculate x in HgClx using a graph of mass of Hg (y-axis) against mass of HgClx (xaxis)?

Question

The experiment observations was as follows: -
-HgClx dissolves in water to form a colourless solution.
-On adding H3PO2 a white suspension forms which rapidly turns to a grey suspension of droplets of metallic mercury.
-On further heating, the suspended droplets merge to form large drops of Hg(mercury) at the bottom of the beaker.

Several experiments was done using different masses of HgClx.

I plotted a graph of mass of Hg against mass of HgClx. Is this correct?
Also I got 0.71818 as slope(gradient) of the graph can i use it to find x in HgClx? If so how?
[Ar: Hg, 201.0: Cl, 35.5]
Thank you for any help in advance.

Answer 1

I very much like that you calculated the slope. Think about what the slope represents: Mass Hg/ Mass HgClx

This is a mass percentage. From your data, 0.71818 means your compound is ~72% Hg by mass.

Therefore, all you need to do is mathmatcially figure out which form of Mercury chloride has a percentage by mass of mercury that is approximately 72%

HgCl would be 201/236.5 = 84.989% mercury by mass.

HgCl2 would be 201 / 272 = 73.89% mercury by mass

HgCl3 would be 201/307.5 = 65.36% mercury by mass

As you can see, the data you have leads us to assume the formula is HgCl2 (also matches up with a common Mercury ion) Obviously there is some error, but being off by only 2% from the actual percentage is quite good. Provo for a well executed lab!