What is (i) #%O# in #"aluminum sulfate"# by mass? And (ii) given a #1.00*g# mass of this salt, how many formula units does this mass represent?

1 Answer
anor277
Jun 17, 2017

Well, #%O="Mass of oxygen in aluminum sulfate"/"Mass of aluminum sulfate"=56%#

Explanation:

#O%=(12xx16.00*g*mol^-1)/(342.15*g*mol^-1)xx100%=??%#

For formula units present in #1.000*g# of the salt, we work out the molar quantity.......

#"Moles of aluminum sulfate"=(1.000*g)/(342.15*g*mol^-1)=2.923xx10^-3*mol#

And since we know that #1*mol# contains #N_A="Avogadro's Number"=6.022xx10^23*"particles"*mol^-1#, we has ..............

#2.923xx10^-3*molxx6.022xx10^23*mol^-1=1.760xx10^21*"formula units"#.

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