[Benjiadd]

It's been a while i'm a mature student (nearly 30) returning to uni to re-train and chemistry is not my strong point I have been given these questions as homerwork for Friday and I have sat and gone through them and I am just really looking for a push in the right direction - I need to know the definitive rules for balancing equations here are the 5 questions presented to us. I'm not sure if I should be balancing charges and not only atoms...I'm a little rusty if someone could help my by not only answering but explaining why that would be appreciated so much! I'm new and hi all and thanks ahead of time!

As I go down the paper the questions get even harder if these can be helped to be answered and I can understand them I will share the ones which would be as well written in a different language as I really am struggling - Thank you kind people of the chemistry forum.

Questions as follows

Below are unbalanced equations of chemical reactions that are of biogeochemical
relevance. Write the balanced stoichiometric equations, showing the steps you take in
balancing the equations. Identify the reactions that are redox reactions

a) H2S + O2 > SO42- + H+
b) Ca2+ + HCO3 → CaCO3 + H2O + CO2
c) SO42- + CH2O + H+ → H2S + CO2 + H2O
d) CH2O + NO3- + H+ → CO2 + N2 + H2O
e) Mn2+ + O2 + H2O → MnO2 + H+
f) H2 + CO2 → CH4 + H2O

Thanks in advance!

Edit - I have answers for the balanced equations themselves this is marked as a 24 point question for A-F  in total - Please someone help me understand.

Edit - Is this higher than highschool I'm unsure? Should I have posted in undergrad? Sorry if wrong section - its beginning of my degree and they said it was end of high school level chemistry

Final Edit - If anyone wants to challenge the stuff I really don't even understand on a basic level that I have been handed out please PM me and i will send through the jargon to you it looks sooooo complicated.. I think ill be a regular around here now anyway atleast for the next 4 years and likely on wards to pass on knowledge that hopefully is passed to me 

[chenbeier]

First you have to figure out which are redox reactions, and which are normal recombinations. Redoxreaction can be seen if different molecules are formed and oxidation numbers are changed.

In number a) you have hydrogen sulfide, oxygen and sulfate. What kind of reaction is this?
Number b) has the same things on both sides. Same question again, what do we have here?
Figure out for the rest of the equations.

Redoxreaction in acidic envirement

Oxidation: add water get H⁺
Reduction add H⁺ get water




 

[Benjiadd]

I only understand half of what you are saying. I really need it laid out in broad terms - remember i'm 12 years out of school and a lot of the terminology is very unfamiliar . Can you break that down a little simpler please.

Thanks

[Borek]

Try to read this: http://www.chembuddy.com/?left=balancing-stoichiometry&right=toc

[Benjiadd]

If im on the correct track. Answer A

H2S + O2 ---> SO42- + H+

H2S + 2O2 ---> SO42- + 2H+

Then the stoichiometric is
Hydrogen (II) Oxygen no charge as its elemental ----> S042-
  (In a compound oxygen has an oxidation numer of -1) Oxygen (-II) Leaving no overall change in oxidisation number meaning no redox has occured?.


I hope this is correct...

[Borek]

H2S + 2O2 ---> SO42- + 2H+

Please use subscripts and superscripts, they are part of the formatting tools. Yes, this is correctly balanced.

Then the stoichiometric is
Hydrogen (II) Oxygen no charge as its elemental ----> S042-

"Hydrogen (II) Oxygen" looks rather strange - we use roman numbers in parentheses to denote valence when the value is not clear. Hydrogen never has a valence of 2, so it is not clear what you are trying to mark with this number.

(In a compound oxygen has an oxidation numer of -1) Oxygen (-II) Leaving no overall change in oxidisation number meaning no redox has occured?

In none of these compounds oxygen has an oxidation number of -1. Why -II? Do you mean just -2?

The linked page contains simple rules to follow when calculating oxidation numbers for each atom in the compound. Oxidation number is a property of a single atom, so there is no such thing as an "overall change in oxidation number".

[Benjiadd]

Sorry I was in a panick and a rushing.

Basically... we are taught that roman numbers represent oxidation state to determine whether redox has occured. That was the basis of the question and I didn't take my time and read up about the rules of oxidation states - e.g - In a peroxide oxygen always has a oxidation number of negative 1 (-I) and also things like O₂ and Cl₂ have oxidation numbers of 0.

Was panic and confusion that got to me... got hit with a huge test today (100 points) to be honest oxidation numbers were the last of my worries - I had never even seen 0th 1st and 2nd order kinetics and it came up....I have a lot to learn. I will be more concise and coherent with my requests next time and will follow forum rules - apologies for double posting. Hopefully I can stick around and grow.

Thanks Borek for the reply and your time