[Chemistry] Number of grams

1. Aug 2, 2008

crays

Hi, i wonder how could i calculate the number of grams of ethanedioate ion, C2O42- in one dm3

Given:
FA1 was made by dissolving 6 g of metal ethanedioate, MC2O4 is dissolved in dilute sulpuhric acid and making up to 1 dm3 with pure water.

FA2 contains 2.38g of manganate (VII) ion per dm3.

25.0 cm3 of FA1 requires 19.65 cm3 of FA2 for complete reaction.

As i'm pretty weak in chemistry, i tried my best to solve the question. I used the (MAVA)/(MBVB) = ratio/ratio method.
But not sure if i'm right.

I also cannot differentiate if its suppose to be concentration or just pure mass. can someone help me here?

FA2 contains 2.38g of manganate (VII) ion per dm3.

does it means it have 2.38g (mass) or 2.38gdm-3 (concentration) ?

2. Aug 2, 2008

Staff: Mentor

First of all - you need balanced equation of reaction between oxalate (ethanodioate) and permanganate (manganate(VII)).

Amount of permanganate in FA2 is given as mass per volume, so it is concentration.

3. Aug 2, 2008

crays

Erm, but it wanted ions. So i use half equation?

2MnO4- + 5C2O42- + 16H+ ----> 2Mn2+ + 10CO2 + 8H2O

Molarity of FA2 = 2.38/119.4

Molarity of C2O42- x 25.0 divided by 2.38/119.4 x 19.65 = 5/2

Correct ?

4. Aug 3, 2008

Staff: Mentor

That's a correct equation. Not a half equation, but a full one.

That's correct, although just dividing you get number of moles. However, mass was given per L, so it turns out the same.

You have lost me here, although it is very likely that you are OK. Just post the final number.