Mole question (2 Viewers)

[wiliaamnguuyen]

Can anyone help me with this? How many moles of aluminium ions and sulfate ions are there when 34.2g of aluminium sulfate is dissolved in 500mL of water?

 

[MilkyCat_]

First find the number of moles of aluminium sulfate using n=m/MM
n(Al2SO43)=34.2/342.15
n(Al2SO43)=0.1

Now find the ratio of the ions in the aluminium sulfate (which is 2Al^3+: 3(SO4)^2-) and multiply these ratios by the original number of moles of aluminium sulfate.

Therefore the number of moles of Al^3+=2x0.1 mol
aluminium ions=0.2 mol
number of moles of (SO4)^2-=3x0.1 mol
sulfate ions=0.3 mol

I don't know why the 500mL is in the question?

 

[AztecWarrior]

@milkycat because there are the ions are only separated in the aqueous solution, mabye a follow up/extension question could be "calculate the concentration of the solution?"

 

[wiliaamnguuyen]

Oh, yeah I was a little confused with the 500mL and didn't know whether to use concentration formula or not. Thanks btw

 

[wiliaamnguuyen]

Can you guys help me with this?
Write down the reaction between sodium and sulfuric acid. The solution is then evaporated with a bunsen burner. He then weighs the salt left behind. Calculate expected mass of salt if reaction was complete.
2Na(s) + H2SO4 (aq) -> Na2SO4(aq) + H2(g)
n(Na) = 4 /22.99
= 0.1739 moles
n(Na2SO4) = 0.08695 moles (ratios)
m(Na2SO4) = 0.08695 x (2(22.99) + 32.07 +4(16))
= 12.35g
Is this correct?

 

[Drongoski]

First find the number of moles of aluminium sulfate using n=m/MM
n(Al2SO43)=34.2/342.15
n(Al2SO43)=0.1





I don't know why the 500mL is in the question?

Included to trick you.