[lucas89]

Hey chemforum. This is my first time posting, but I have a feeling I'll be around much more as this website seems quite useful .

I have an intro inorganic chemistry lab write up, and I'm stuck on the overall equation for the reactions. There's a help center at my university to ask instructors for help with these topic, but I was sick today, and hence unable to go. But here we go:

Anyway, we're synthesizing Barium iodate monohydrate, Ba(IO3)2 H2O. First we added Sodium chlorate, NaClO3(s), powered Iodine, I2(s), and Nitric acid, HNO3(aq) to a kjeldahl flask, and heated with an open flame. After heating, we poured the solution into a beaker, heated on a hot plate, and added a hot solution of Barium nitrate, Ba(NO3)2(aq) to this solution, giving us our product, which we then isolated via. suction filtration.

I have a few hints on the reaction. During the initial heating process in the kjeldahl flask, I observed both purple and yellow/green gas being evolved from the solution, leading to believe that chlorine and iodine gas was evolved during the heating. It also states in the lab manual that NaClO3 is used to oxidize the solid I2. Finally, I know that the nitric acid is only added to allow the reaction to proceed in an acidic medium. All of this leads me to believe that there's definitely some redox happening here, but other than that, I've hit a brick wall on the reaction. Can anyone help?

Thanks in advance!

[Arkcon]

Good observations.  Can you take the words, and break them down into chemical formulas, string those chemical formulas into chemical equations, and balance them?  Then we may be able to predict the red-ox.

[lucas89]

Okay, I can take a go here. Another observation I left out, which may be somewhat useful: the iodine gas begun to solidify on the neck of the of the flask, which then ran back down into the solution when the refluxing Cl2(g)/steam would enter the flask neck.

But, we start off with NaClO3(s) + I2(s) + HNO3(aq) + heat.

Since I2 and Cl2 were noticed as gases in the reaction, we know that I2(g) and Cl2(g) must be products here, for the first part of our reaction anyway. Now, I'm unsure whether the nitric acid will react in the reaction at all, since it's only used as a medium. No tests were done for oxygen gas, so there's no valid way I can state if it'll be present. However, if the ClO3- is being broken apart to give chlorine gas, would it be safe to assume that oxygen gas is also produced?

[Arkcon]

Good instincts, now, what are you trying to make?  What do you need to make it?  You add barium nitrate as a last step, to provide barium.  What needs to be there first?  Also, since this is red-ox, what is gaining electrons, and what is losing them?

[BluRay]

Also, consider that chlorates + strong acid are usually used as a strong oxidant (in this sense which acid is irrelevant).
About chlorine and/or oxygen released, compute the oxidation numbers of all the species and try to understand which is the oxidant and which the reducing.

[lucas89]

Thanks for the help everyone. I sat down before my lab exam today and worked on my write up a bit more, and then ran over to the help center to ask if I was right.

The equation is in two parts, first being:
NaClO3 + I2 -> Cl2 + IO3- + Na+

and then the second being:
Cl2 + IO3- + Na+ +Ba(NO3)2 -> Ba(IO3)2 H20 + NaNO3

Just got the overall equation after that by adding them.

From there, I got the oxidation/reduction and whatnot, and I'm all good to go. Thanks for the help guys!