i love chemistry, but back-titration kills me, help!
 

i've finished 3 subjects of chemistry but i always seem to be late or absent in class whenever thry're discussing back-titration...

i have a problem that i can't answer, i know that i should start with knowing the ratio and proportion of the titrant and the intermediate reagent, but i'm confused what to do since the molarity and the volume of the intermediate reagent is also given, i hope someone whould help me...

==An 800 mg sample of chromium ore was dissolved and the chromium oxidized to chromate ion. The solution was treated with 10 ml of.200 M AgNO3. The resulting precipitate of Ag2CrO4 was removed and dissolved. The excess AgNO3 required 14.50 mL of .1200 M KSCN for titration. Calculate the % Cr2O3 in the ore.

whew, anyway i know that the equation should be

CrO4 + 2Ag --> Ag2CrO4 and then Ag + SCN --> AgSCN

i'm really confused on the role of the given Molarity and volume of the Intermediate reagent, i can't seem to pick my way up to knowing the mass of Cr2O3 to be divided by the given g sample of chromium ore...

i have a major exam coming up and i'm afraid they might ask qestions on back-titrations and i wouldn't know how to answer,,,

please help me anyone? thanks so much! =)

the most important in back titrations is the you keep in mind what the titration is about.

First you need to make the balanced titrationreaction equation. you add an excess of a component. The excess is titrated. So in fact your are determining the amount that didn't react, because the compound that you want to determine has completely reacted.

--> you know what you added and what is left, so in this way you can calculate how many mols of the compound you are interested in has reacted.

Hope this helped you further.