[shinjo]

What weight of pyrite ore (impure FeS2) must be taken for analysis so that the BaSO4 precipitate weight obtained will be equal to one-half that of the percent S in the sample?
 
that's all the given.. how then to solve this?

[Borek]

First, try to write the condition (mass of precipitate equal to half percent S in the sample) in the form of mathematical equation.

m_BaSO4 = ...

[shinjo]

thanks sir, then after? i really find it hard to start because there are no numbers involved in the problem..
if it's okay with you sir, would you please elaborate your explanation a little bit?

[Borek]

Don't sir me

Solve using symbols first. I already showed you first symbol to use - mass of precipitate. Sooner or later you will need to
use molar masses of substances and stoichiometric coefficients of the reactions involved - these will be your numbers.

[shinjo]

Thanks Mr. Borek.. One last question.. after setting up the equation the next thing to do is to get the %S of the sample using percentage composition of compound.. i'm wondering if what compound of sample will i be use to get the %S. Is it the compound
FeSO4 ? or BaS2 ? or FeS2 ? or BaSO4 ?...

[Borek]

No idea what you are asking about. You weight BaSO₄, you calculate a percentage of FeS₂. Amount of BaSO₄ is in a stoichiometrical relation to FeS₂.

[shinjo]

i still don't get it..sorry   , you mean i have to get first %FeS2? i thought first thing to do is to get %S then from the equation
m_BaSo4=1/2(%S) i could now get the mass/weight of BaSO4... so, basically i really have to get first %FeS2 but how?

[Borek]

Assume you know mass of the precipitate (m_BaSO4) and mass of the sample (m_sample). Can you write equation that will use these two quantities to give S percentage in the sample?