Sciencemadness Discussion Board - Number of atoms - Powered by XMB 1.9.11 (Debug Mode)

Number of atoms

blink182 - 11-4-2013 at 14:27

My question is:

How come
or
Why
Does

100 grams of tcca have less chlorine than
100 grams of ca(ocl)2
when
tcca has 3 atoms of chlorine, and ca(ocl)2 has 2 atoms of chlorine

Mailinmypocket - 11-4-2013 at 14:33

And how many other atoms does each molecule have?

DraconicAcid - 11-4-2013 at 14:35

Calcium hypochlorite has two atoms of chlorine in its formula unit. This has a molar mass of 142.99 g/mol, so there are 0.699 moles of it in 100 g, which means there are 1.40 moles of chlorine atoms in it (8.4 x 10^23 atoms).

To do the same calculation with "tcca", I'd have to know what it is, but if it has a molar mass of much larger than that of calcium hypochlorite, then those three atoms would be in a much larger mass, so 100 g would have much fewer moles 9and thus fewer chlorine atoms).

elementcollector1 - 11-4-2013 at 14:40

trichlorocyanuric acid?

blink182 - 11-4-2013 at 15:03

Quote: Originally posted by Mailinmypocket

And how many other atoms does each molecule have?

I dont understand how that would be relevant?

now i think i get it, the proportion of the chlorine's weight to the other weight in the molecule is higher in calcium hypochlorite then trichlor

is that the reason why?

[Edited on 11-4-2013 by blink182]

DraconicAcid - 11-4-2013 at 15:09

Quote: Originally posted by blink182

Quote: Originally posted by Mailinmypocket

And how many other atoms does each molecule have?

I dont understand how that would be relevant?

Because of that 100 g, only some of it is chlorine. If you have chloroform (HCCl₃), then 89.1 of those grams are chlorine, and the rest is carbon and hydrogen. If you have trichlorotriiodoethane (CCl₃CI₃), then you still have the same three atoms of chlorine, but the mass of the other atoms is so much greater that there will only be 20.8 g of chlorine in the 100 g.

Eddygp - 1-5-2013 at 07:43

Yes, it's basically stoichiometry. It's relative to the number of atoms in the whole molecule, not only how many chlorine atoms there are. A trichlorodecane molecule will weigh more than a trichloromethane, and even though it has the same number of atoms of chlorine PER MOLE, 100g of it will have different amounts, because 1 molecule of one weighs different from the other.

AJKOER - 8-5-2013 at 06:47

OK, there is a concept of 'available chllorine'. It is defined (source: http://www.merriam-webster.com/dictionary/available%20chlori... ) as follows:

"the amount of free chlorine that a substance (as bleaching powder) yields when treated with an acid in the presence of a chloride (as sodium chloride or calcium chloride), one atom of chlorine in a hypochlorite being thus computed as equivalent to a molecule of elemental chlorine"

Assume you have a mixture of NaOCl and NaCl (found commonly in chlorine bleaches) as follows:

1. NaOCl 5% NaCl 4%
2. NaOCl 2% NaCl 15%
3. NaOCl 6.25% NaCl 2%

Then which mixture has the highest available chlorine to liberate Chlorine gas with H2SO4?

The answer: first some chemistry on how actually the Cl2 is formed:

NaCl + H2SO4 --> NaHSO4 + HCl
NaOCl + H2SO4 --> NaHSO4 + HOCl
HCl + HOCl --> H2O + Cl2 (g)
-------------------
Net:
NaCl + NaOCl + 2 H2SO4 --> 2 NaHSO4 + H2O + Cl2 (g)

So the mole formation of Chlorine is the lower of the number of moles of (NaCl, NaOCl). But, if there is an excess of chloride and acid present, each Cl from the hypochlorite is available to form a mole of Cl2.

This is only the case for choice (1). Choice (3) is not the answer as the possible higher generated amount ('available') chlorine is not achievable, in fact, due to the lower NaCl content (which promotes stability of the bleach along with a higher pH obtained by adding NaOH or Na2CO3 to the bleach), and we are, by definition, measuring actual amount of chlorine formed.

[Edited on 8-5-2013 by AJKOER]

ScienceSquirrel - 8-5-2013 at 07:18

Available chlorine is defined here;

http://www.cloroxprofessional.com/products/ultra-clorox-germ...

An assay for it is given here;

intranet.wellingtoncollege.org.uk/resource.aspx?id=15677

AJKOER's post is wrong, chloride ion is NOT required to liberate chlorine from bleach.

woelen - 8-5-2013 at 07:38

But for the concept of 'available' chlorine, additional chloride ions ARE needed. A nice example is LiOCl, which has available chlorine of more than 100%!

All these definitions look very difficult, but they are equivalent to the following very simple thing:
- Take 100 gram of your compound.
- Add excess amount of HCl.
- Determine how many grams of ELEMENTAL CHLORINE is formed (disregard other forms of chlorine).

Available chlorine is (amount of elemental chlorine)/100 gram.

An example:

LiOCl reacts with HCl as follows:

LiOCl + 2HCl --> LiCl + H2O + Cl2.

When there is excess HCl, then 100 grams of LiOCl leads to formation of 121.43 grams of Cl2. Hence, the available active chlorine of pure LiOCl is 121.43%.

Another example:

TCCA reacts with HCl to form cyanuric acid and Cl2:

C3O3N3Cl3 + 3HCl --> C3O3N3H3 + 3Cl2

100 grams of TCCA in excess HCl gives 91.53 grams of Cl2. Hence, the available active chlorine of pure TCCA is 91.53%.

AJKOER - 8-5-2013 at 08:04

ScienceSquirrel:

Your source (Chlorox) is, in my humble opinion, not on the same level as Merriam Webster, which respect to the potential for product marketing bias. However, I do admit that my cited definition is a bit dated referring to the use of bleaching powder. More increasing common in the USA for swimming pools, for example, is the use of trichloroisocyanuric acid (TCCA), which slowly reacts with water forming HOCl (and yes, absence any chloride) being the source of the bleaching/disinfectant properties, and not chlorine (which slowly forms HCl and HOCl in water). However, as HCl reacts with TCCA to produce Chlorine, the definition can still be viewed as meaningful.

Now, if one subscribes to the definition of 'available chlorine' as meaning forming free chlorine, than TCCA (alone no acid) actual forms only very slowly free Cl2. The reason is only HOCl is formed, and only upon its decomposition to HCl and Oxygen (and not HCl and HClO3), can any Cl2 be directly formed.

Your other UK reference appears to imply that hypochlorite has been replaced with chlorate. This certainly is not the case in the United States, so we may have some interesting geographic issues.

[Edited on 8-5-2013 by AJKOER]

ScienceSquirrel - 8-5-2013 at 08:04

I agree with that equation Woelen, but I believe that for the purpose of assaying bleach for available chlorine the following reaction is used;

4H+(aq) + 2ClO– (aq) + 2e- ---> Cl2(aq) + 2H2O(l)

ScienceSquirrel - 8-5-2013 at 08:24

Quote: Originally posted by AJKOER

ScienceSquirrel:

Your source (Chlorox) is, in my humble opinion, not on the same level as Merriam Webster, which respect to pothe tential for product marketing bias. However, I do admit that my cited definition is a bit dated referring to the use of bleaching powder. More increasing common in the USA for swimming pools, for example, is the use of trichloroisocyanuric acid (TCCA), which slowly reacts with water forming HOCl (and yes, absence any chloride) being the source of the bleaching/disinfectant properties, and not chlorine (which slowly forms HCl and HOCl in water). However, as HCl reacts with TCCA to produce Chlorine, the definition can still be viewed as meaningful.

Now, if one subscribes to the definition of 'available chlorine' as meaning forming free chlorine, than TCCA actual forms only very slowly free Cl2. The reason is only HOCl is formed, and only upon its decomposition to HCl and Oxygen (and not HCl and HClO3), can any Cl2 be directly formed.

Your other UK reference appears to imply that hypochlorite has been replaced with chlorate. This certainly is not the case in the United States, so we may have some interesting geographic issues.

[Edited on 8-5-2013 by AJKOER]

I like manufacturer's technical product sheets, they get sued if they get it wrong. Mirriam Webster can make lots of mistakes with not a lot to fear.
Chlorate I is hypochlorite, just as Chlorate V is chlorate and chlorate VII is perchlorate.

AJKOER - 8-5-2013 at 09:14

I may be alone in this assessment, but I am increasing starting to view net ionic (and even a summary net reaction) equation as 'bad' chemistry. Not listing the reaction sequence, and thereby limiting ones' focus/awareness of intermediate products without full attention being paid to their properties (especially stability) detracts from a reaction's potential success and safety, in my opinion.

For example, in the reaction sequence presented above, I clearly demonstrated the formation of Hypochlorous acid. Knowing the properties of HOCl, one should not knowing create it in concentrations exceeding 30%. So working with Sodium hypochlorite hydrate (or a solid hypochlorite), and concentrated H2SO4 could easily produce an incident as the chemist is thinking of Cl2, and not of the unstable HOCl.

There was also an equally dangerous intermediate situation I disclosed recently (see http://www.sciencemadness.org/talk/viewthread.php?tid=23193#... ), also not completely apparent, in this case, in the net reaction summary equation.

Bottom line, I would avoid net ionic equation or a summary reaction presentation, except in a purely academic setting.

[Edited on 8-5-2013 by AJKOER]

woelen - 9-5-2013 at 13:11

Quote: Originally posted by ScienceSquirrel

I agree with that equation Woelen, but I believe that for the purpose of assaying bleach for available chlorine the following reaction is used;

4H+(aq) + 2ClO– (aq) + 2e- ---> Cl2(aq) + 2H2O(l)

This is a partial equation. Where do the electrons come from?

The usual practical method to assay bleach for available chlorine is to take excess amount of acidified solution of KI and add a known volume of bleach. This leads to formation of iodine. This iodine then is titrated with thiosulfate. The titration shows how much iodine is formed from a certain amount of bleach. Each atom of iodine then is replaced by an atom of chlorine in the computation of "available chlorine". If you do the computations, then you'll see that you end up exactly with the definition of my previous post. Each ClO(-) ion leads to formation of one molecule of I2 and hence to one molecule of Cl2 in the computation of available chlorine.

ScienceSquirrel - 10-5-2013 at 04:02

Acetic acid is the usual acid used and the reaction is;

4H+(aq) + 2ClO- (aq) + 2I- ---> I2(aq) + 2H2O(l) +2Cl-

Please read the assay for available chlorine at;

intranet.wellingtoncollege.org.uk/resource.aspx?id=15677

Your reaction is correct, hydrochloric acid will react with one molecule of hypochlorite to form a molecule of chlorine but it is not the basis for the assay of available chlorine.

woelen - 10-5-2013 at 08:29

Your reaction is not corrent. At the left there is zero charge, at the right there is charge -2. If you write the correct equation, then you'll see that there are two iodide ions oxidized by one hypochlorite ion and if that is used for assaying available chlorine, then you get something which is exactly equivalent to what I wrote before.

The definition indeed is based on the iodine, but in practice, my (equivalent) interpretation is easier to grasp.