Chemistry C2 AQA

Number of moles  =  Mass(g)  /   Ar/Mr

2 HgO ----> 2Hg  +  O2

Mass

HgO  =   117

          (101+16=117)

a)What mass of Mercury (Hg) is formed from 21.7g of HgO?

Step1)  Use mass/g from Q to find n.o of moles.

            Number of moles of HgO = 21.7/217 = 0.1 moles of HgO

Step 2) Use the equation to find ratio to tell you how many moles of theone you are calculating.

0.1 moles HgO  :   0.1 moles Hg

0.1 moles Hg    :   0.05 moles O2

Step 3) Use number of moles from step2 and find mass/g of Hg.

0.1 = mass(g)/201    mass of Hg = 201*0.1=20.1Hg

21.7-20.1=1.6g of O2

0.05 = mass(g) / 32

Mass of O2/g = 32*0.05=1.6g