[Laker12]

A .242 g sample of potassium is heated in oxygen. The rest is .440 g of a crystalline compound. What is the formula of this compound?

I'm a little confused as to how to use the given information to find the formula. Do I use the molar mass of oxygen to turn into moles? Even then I'm not sure what to do about the rest.

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These three equations describe an oxidation reduction method for determining dissolved oxygen in water. How many moles of S203- (S2O3 with a negative 1 charge) are equivalent to each mole of O2?

1. 2Mn(2+) [aq] + 4OH(-) [aq] ---> 2MnO2 + 2H2O [l]
2. MnO2 + 2I (-) [aq] + 4H (+) [aq] ---> Mn(2+) [aq] + I2 [aq] + 2H2O [l]
3. 2S2O3(2-) [aq] + I2 [aq] ---> S4O6(2-) [aq] + 2I(-) [aq]

To be honest, this one completely puzzles me. I'm at a loss for even which method to use to solve this problem.

Thank you in advance.

[Borek]

A .242 g sample of potassium is heated in oxygen. The rest is .440 g of a crystalline compound. What is the formula of this compound?

Follow the path:

Potas mass. Moles of potas. Mass of oxygen that reacted. Moles of oxygen. Formula.

These three equations describe an oxidation reduction method for determining dissolved oxygen in water. How many moles of S203- (S2O3 with a negative 1 charge) are equivalent to each mole of O2?

No oxygen in these reactions, no such compound as S₂O₃^-, no wonder you have no idea what to do. Check out first reaction - it is not balanced.

[Laker12]

I got the first one, thanks.

As far as the second one, that was a mistake on my part. Here's the right info:

1. 2Mn(2+) [aq] + 4OH(-) [aq] + O2 [g] ---> 2MnO2 + 2H2O [l]
2. MnO2 + 2I (-) [aq] + 4H (+) [aq] ---> Mn(2+) [aq] + I2 [aq] + 2H2O [l]
3. 2S2O3(2-) [aq] + I2 [aq] ---> S4O6(2-) [aq] + 2I(-) [aq]

Sorry about that.

[Borek]

Simple stoichiometry now. 1 oxygen molecule gives 2 molecules of MnO₂. 2 molecules of MnO₂ give ... molecules of I₂. ... molecules of I₂ react with ... molecules of thiosulphate.

Just fill the blanks.

[Laker12]

This is going to sound stupid, but why does 1 oxygen molecule give up 2 molecules of MnO2?

[Borek]

This is going to sound stupid

I am not denying

but why does 1 oxygen molecule give up 2 molecules of MnO2?

See first reaction equation - how many oxygen molecules on the left? How many MnO₂ molecules on the right? That's stoichiometry. See stoichiometric calculations - 2nd paragraph is about reading the balanced reaction equation.

[Laker12]

I can appreciate honesty.

Now let me see if I understood it correctly from that site. Would 2 molecules of MnO2 produce 2 molecules of I2 since in that second equation there is 1 molecule of MnO2 and 1 molecule of I2?

[Borek]

Would 2 molecules of MnO2 produce 2 molecules of I2 since in that second equation there is 1 molecule of MnO2 and 1 molecule of I2?

Exactly!

[Laker12]

Beautiful, I got it, you're the man.