Stoichiometric reactions with weight percent

1. Feb 17, 2012

emc92

How many grams of 6.000 wt% aqueous HF are required to provide a 50% excess to react with 10.0 mL of 0.0236 M Th4+ by the following reaction?

Th(4+) + 4F - → ThF4 (s)

I found the molarity for Th(4+) to be 2.36*10^-4.. I'm not really sure where to go from here =/

2. Feb 17, 2012

Staff: Mentor

How many moles of F- do you need? What mass of HF will contain this number of moles?

3. Feb 17, 2012

emc92

i tried to solve it again..
i came up with 0.627g. is this right?

4. Feb 17, 2012

Staff: Mentor

Show how you got it.

5. Feb 17, 2012

emc92

using the moles of Th, i multiplied that by 4 to find the number of moles of HF, which turns out o be 9.44*10^-4. Then i changed it to grams, giving me 1.88*10^-2g. since it said 50% excess, the total grams of HF would be 0.376g. then 6 %wt would be 0.627g

6. Feb 17, 2012

Staff: Mentor

OK up to now.

You ate zero, but I think I know what you did. 50% excess and 100% excess are two different things.