Question

1.11 g of ca cl2 added to water forming 500ml solution. 20ml of this solution is diluted 10 folds. find the moles of cl- in 2ml diluted Solution?

Answer 1

`n_"chloride"=8*mumol`

Explanation:

`"Moles of calcium chloride"=(1.11*g)/(110.98*g*mol^-1)=0.0100*mol`

...the which is then dissolved in solution...to give a concentration, `-="moles of solute"/"volume of solution"=(0.0100*mol)/(500*mLxx10^-3*L*mL^-1)=0.0200*mol*L^-1`

And then `20*mL` of this solution is diluted tenfold...

`[CaCl_2(aq)]=(20xx10^-3*Lxx0.0200*mol*L^-1)/(200*mLxx10^-3*L*mL^-1)=0.00200*mol*L^-1`...

And the question wants to know how many moles of chloride there are in `2*mL` of this solution....

`n_"chloride"=2xx10^-3*Lxx0.00200*mol*L^-1xx2=8.00xx10^-6*mol`...

...why did I multiply by `2`?