Question

how do i calculate %of arsenic and oygen by mass and chem composition of the oxide
that has been formed
0.702 sample of arsenicheated, material in boat, oxide of arsenic with mass of 0.927g

please help

%As = [(mass As)/mass oxide]x100=??
%O = [(mass O)/mass oxide]x100=??

From your data, it appears mass As = 0.702g and mass of oxide is 0.927g. Check me out on that. I may not interpret your numbers correctly.

thanks but is it 0.702/ 0.927 = 75.728155

but what figures do i use to work out the % of oxygen


If 0.927 g is the mass of the As after heating (and the mass of the boat is not in that number, I hope), then 0.927 - 0.720 = mass oxygen that must have been added. Right?

am i right in saying that
% as is 0.702 divided by 0.927 x 100
= 75.7%


and the %oxygen is 0.927 - 0.720
= 0.0207 divided by 0.927
= 0.22%


or am i really thick lol


sorry i forgot to x it by 100

so is the answer 22.33 %

Yes, 75.7% As is correct.
I'm afraid I made a typo in my last post and you didn't catch it.
mass oxygen = 0.927 - 0.702 <b>(not 0.720 as I typed)</b>= 0.225, then
% oxygen = (0.225/0.927)x100 = a little different than 22% but not by much. Of course you know that %As + %O should add to 100%.

Hallo cheating S103 'student'Try reading B6