Arsenic trihydride reacts with oxygen gas to produce Arsenic monoxide gas and water vapor.
During the reaction, (x) g of arsenic trihydride react with excess oxygen gas to
produce (y) g of arsenic monoxide. Determine the percent yield.
(x) = 15.0 grams
(y) = 7.78 grams

h let me think

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.