[funboy]

Im new to this forum, and just as new to chemistry.  The last time I touched chemistry was 12 years ago.

I understand how to apply the reaction types for the exception of calculating the # of moles per compound in the product.

IE

H3PO4--->P2O5 H2O

when decomposing H3PO4, how did we get 2 moles of P and 6moles of O??

or

CO2 + H2O -----> C6H12O6 + O2

how do I calculate the moles per element in the product based on moles per element in the reaction?

Thanks.

(if you can think of a link that explains this procedure, I would be thankfull)

[hmx9123]

Remember that more than one molecule of reactant can make the products.

Also, while I guess you could calculate 'moles per element' of each element, usually you're concerned with either percent mass of each element in the final compound or more commonly, the number of moles of reactants and products.

Are you still sure this is what you wanted to ask about?

[Borek]

Check out these lectures on reaction balancing and stoichiometric calculations, they should help you understand what is wrong with your question:

http://www.chembuddy.com/?left=balancing-stoichiometry&right=balancing-reactions

[funboy]

not so much,

esentially I want to be able to determine the product based on the reaction.  I understand the concept of synthesis, decomposition, single/double replacement.  But I cant seem to get the right number of moles in the product.

Example

what is the product when lithium oxide reacts with chloric acid ??

or

what is the product when carbon dioxide reacts with water??

How do I do this without software??

[Borek]

But I cant seem to get the right number of moles in the product.

That's reaction balancing, covered in the lectures.

what is the product when lithium oxide reacts with chloric acid ??

That's completely different question - you are asking how to prepare skeletal reaction. In general there is no universal way to predict how the reaction will proceed. For many reactions there are rules that will help you find out what products you may expect, but there are tons of these rules, and tons of the exceptions to them.

Metal oxides react with acids yielding water and salts, thus in your case skeletal reaction looks like

Li₂O + HCl -> LiCl + H₂O

it is not balanced yet, so there is no answer to your question about numbers. Once we will balance it, yielding

Li₂O + 2HCl -> 2LiCl + H₂O

numbers of moles are given as well.

[funboy]

Sorry for all the confusion (as Im confused).

I can balance equations providing reactions and products are given.

Its when the product isnt given

Facts such as

"Metal oxides react with acids yielding water and salts"

are something I need to familiarize myself with.  What would I google to get a list of these rules/facts??

[Borek]

Facts such as

"Metal oxides react with acids yielding water and salts"

are something I need to familiarize myself with.  What would I google to get a list of these rules/facts??

I am afraid you will not find these rules listed, as that's what the chemistry is about - and you need several years of learning to master it to a reasonable degree. There are several simplified rules like this one, but they cover only small subset of reactions you may see in the real life, plus (due to simplification) they are easily falsified by counterexamples.

Look for some general chemistry books (there was a thread with books listed somewhere in the forums) or general chemistry sites (General Chemistry Online comes to mind).

[funboy]

Im making great progress here, I understand decomposition, synthesis and single/double replacement.  I found a great tutorial on the topics with examples.

The one thing that Im still having a difficult time figuring out is the oxidation numbers(of the product).

For decomp and synthesis it was easy enough for me to just memorize sets of reactions to figure out the product

ie: SO2 produces H2SO3, SO3 produces H2SO4 and so on

But when I get to single/double replacement having an understanding of oxidation numbers seems essential.

I know how to use the oxidtion numbers to determ the negative and positively charged elements but dont understand how to use them to get the product

Example

Fe + HCl------>

Fe can be +2, +3 (so the example chooses +3)
Cl is -1

so Fe + HCl-----> FeCl + H

now to figure out the oxidation numbers I cant, the answer is

FeCl3 + H2

but no matter how many answers I reverse engineer I cant find the method for determining the values

What else should I be reading??

[Will]

Example

Fe + HCl------>

Fe can be +2, +3 (so the example chooses +3)
Cl is -1

so Fe + HCl-----> FeCl + H

now to figure out the oxidation numbers I cant, the answer is

FeCl3 + H2

but no matter how many answers I reverse engineer I cant find the method for determining the values

What else should I be reading??

The reaction should be written as Fe³⁺_(aq) + HCl_(aq) --->

as you are given the ox. no. of Fe (I think that's what you meant?), and since this is the only element in that species then that is the charge (+3).

You correctly stated the ox. no. of Cl, so how many chlorines do you need to 'balance' the 3+ charge of Fe?

That is why FeCl₃ is one of the products. I think the other product should be H⁺ not H₂, so you get:

Fe³⁺_(aq) + HCl_(aq) ---> FeCl_3(aq) + 3H⁺_(aq)

However, you may mean Fe metal + HCl, so the ox. no. of Fe is 0. However the correct products of the reaction would be FeCl_2(aq) + H₂ as far as I know. I always thought you have to react Fe with Cl₂ to get FeCl₃.

Which element can't you work out the ox. no. for?

[funboy]

I think its all been put together for me

thanks

I will try a couple test questions and if I get the right answer, im golden

thanks again

[Borek]

I supppose the reaction of iron with hydrochloric acid should be dissolution (unbalanced):

Fe + HCl -> FeCl₂ + H₂

funboy: this is a classical redox, Fe and H change oxidation number (see the ChemBuddy lecture for details on their calculation).

Will: Fe dissolved in any acid (oxidized with H⁺) goes to Fe²⁺. But to oxidize it further you may use just O₂, no need for Cl₂. That's why Fe²⁺ is unstable in water solutions if exposed to atmospheric oxygen

[Will]

Will: Fe dissolved in any acid (oxidized with H⁺) goes to Fe²⁺. But to oxidize it further you may use just O₂, no need for Cl₂. That's why Fe²⁺ is unstable in water solutions if exposed to atmospheric oxygen

Thanks Borek.

I just based my thoughts on woelen's expertise.

The +2 oxidation state is mildly reducing. Solutions of this are stable with respect to aerial oxidation, but when it is precipitated as hydroxide, then it suddenly becomes very sensitive to aerial oxidation.

I would've thought in such acidic conditions FeCl₂ would be fine, and any Fe(II) that is oxidised would end up as rust rather than FeCl₃ as it is the hydroxide which gets oxidised. I am not so sure though, any feedback would be great as my book doesn't even mention it.

[Borek]

The +2 oxidation state is mildly reducing. Solutions of this are stable with respect to aerial oxidation, but when it is precipitated as hydroxide, then it suddenly becomes very sensitive to aerial oxidation.

I would've thought in such acidic conditions FeCl₂ would be fine, and any Fe(II) that is oxidised would end up as rust rather than FeCl₃ as it is the hydroxide which gets oxidised. I am not so sure though, any feedback would be great as my book doesn't even mention it.

I would say it all depends on how you define "stable". Thermodynamically stable state in the presence of O₂ is Fe³⁺. Fe²⁺ can be only kinetically stable - and whether it is 'stable' or not for your needs depends on circumstances. For example whenever you need Fe²⁺ solutions in analytical chemistry you are advised to check their concentration often - so they are considered not stable.

[Will]

I see, thanks again Borek!

Just one thing; would you end up with rust when the Fe(II) is oxidised like that, or would you get FeCl₃?

[Borek]

Just one thing; would you end up with rust when the Fe(II) is oxidised like that, or would you get FeCl₃?

It will depend on pH and Fe(OH)₃ solubility.