CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Someone check specific gravity calculations for me?
Hallo,
Measured 150mL of CUCl2 solution, it weighed 158.8grams.
Ideal SG of CUCl2 is between 270g and 360g per litre.
1 litre/150mL = 6.66 (recurring)
158.8 - 150 = 8.8
Therefore: 8.8 x 6.66 = 58.6grams of copper in 1 litre of the complete CUCL2 solution).
(I know a hydrometer is better but can not lay my hands on one at this moment, but I wanted to get used to maths and chemistry calculations and
searched for an alternative way of measuring the amount of copper in the solution, learning this way also gives me flexibility in other areas of
chemistry, hope you understand and forgive any naivety that is exposed in my thinking)Thanks. I also bet that I am wrong! But have to start
somewhere.
[Edited on 21-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
adamsium
Hazard to Others
Posts: 180
Registered: 9-4-2012
Location: \ƚooɿ\
Member Is Offline
Mood: uprooting
|
|
Your calculations seem correct. Although, I believe that, in practice, when some substances are dissolved, the volume actually changes, but only very
slightly. You'd probably need to use other means to calculate an exact quantity of dissolved salt in a given volume, but what you've done should
suffice here.
Also, with calculations such as this, you may find it easier to just convert the units of your quantities to those which will give the desired
(derived, in this case) units from your calculation. In this case, since you want grams per litre, you could convert the volume to litres (150 mL =
0.150 L). You then get density (mass per volume) = 158.8 g/0.150 L = 1058.7 g/L. Subtracting 1000 g/L for the water (again, we're assuming no change
in volume when dissolving the salt and a density of water of 1.000 g/mL) gives you your 58.7 g of salt per litre of solution. Note that this is no
more 'correct' than what you did - it might just save you some calculations.
As an aside - I really admire your eagerness to learn the actual chemistry of what you're doing. It's really very refreshing to see! And don't ever
feel naive or silly for asking questions - there are no silly questions; only silly answers.
Edit: By the way, what exactly do you mean by "Ideal SG of CUCl2 is between 270g and 360g per litre."?
[Edited on 21-7-2012 by adamsium]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Hi Adamsium, well firstly I am shocked!! I spent half an hour working out how to work out my problem. The SG is the specific Gravity of copper in
the CUCl2 etchant solution/the amount of dissolved Copper per litre. The amount of dissolved copper in the Etchant solution affects etching time which
means less consistency and accuracy regarding depth of cut. A chemical website dealing with small industrial scale etchants mentioned these magical
figures without explaining how they arrived at them other than with a hydrometer. So I took myself to task to work it out myself.
[Edited on 21-7-2012 by CHRIS25]
Yes, just trying to work out how much CU2(OH3)Cl (copper oxychloride) I would need to bring up the density to around say the 100g/L mark. I see the
density for oxychloride is 3.5g/L and molar mass 213g/mol, the latter being irrelevant for this purpose since I do not know the moles of my solution.
Anyway can not figure out what maths are required here. Instinct tells me to simply add 42 grams per litre, but it can't be that simple, I am busy
looking for catches. Also being that there are 3 hydroxyl ions here that would dissociate and add to the water content in effect reducing (probably
by not very much) the actual density achieved to a little less than 100g/L, but that does not matter, I am after general rules and principles and will
leave intircacies and bone picking until I am more experienced.
[Edited on 21-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
adamsium
Hazard to Others
Posts: 180
Registered: 9-4-2012
Location: \ƚooɿ\
Member Is Offline
Mood: uprooting
|
|
It sounds like you're referring to concentrations as weight per volume rather than densities here. I can't imagine any aqueous solution weighing 3.5
g/L! I suspected this might have been the case with the part that I quoted above. 3.5 g/L could also be expressed as 0.35% w/v and 270 g/L as 27% w/v.
(e.g. for 3.5 g/L... 3.5g/1000mL = 0.0035 then simply convert to a percentage by multiplying by 100 = 0.35% w/v).
Assuming it's concentration in g/L you're talking about, you just need to weigh out the desired weight of solute, place it in a suitable vessel (if it
needed to be very accurate, you'd use a volumetric flask, but this would probably be overkill here - a measuring cylinder would probably suffice, but
if you have a volumetric flask, you could use it) and fill to make the total volume up to 1 L, while ensuring that all of the solute has dissolved. If
you don't have a 1L vessel, you can scale down (or up) as appropriate by changing the solute mass by the correct ratio.
You don't need to worry about moles when calculating weight per volume. As the term implies, it's based simply on weight of solute per volume (1 L) of
solution (solution, NOT solvent). You could, however, easily convert this to a molarity using the molar mass of the solute. If you know you have x g
of a solute with a molar mass of 213 g/mol per litre of solution, you can easily convert this to the number of moles you have per litre of solution,
from which you can get the molarity (well, in this case, that would *be* the molarity). So, you need to know: the mass of solute per litre of solution
and the molar mass of the solute. Try working it out for your example of 270 g/L or 370 g/L (or some other amount) with the relevant molar mass, and I
will give you a further hand if need be.
The reverse of this is how we make up standard solutions. After determining the desired molarity (in moles per litre), we convert the desired number
of moles per the desired volume of solution to be made to a mass using the molar mass of the substance, then add water to make up the exact volume of
solution on which our calculation was based (can be anywhere from a few mL to a number of litres - volumetric flasks come in a wide range of sizes).
[Edited on 21-7-2012 by adamsium]
|
|
|
bbartlog
International Hazard
Posts: 1139
Registered: 27-8-2009
Location: Unmoored in time
Member Is Offline
Mood: No Mood
|
|
| Quote: | Hallo,
Measured 150mL of CUCl2 solution, it weighed 158.8grams. |
OK, so far so good...
| Quote: | | Ideal SG of CUCl2 is between 270g and 360g per litre. |
Say what? SG would seem to stand for specific gravity (density), but the units/amounts you give are for amounts of dissolved solid.
No, you can't do the calculation this way. The fact that the units don't match (subtracting ml from grams) is a clue. It looks like you have assumed
that the excess weight (or density) present in the solution can be imputed exactly to the presence of dissolved salt, i.e. that the volume changes not
at all when the CuCl2 is added. This is not the case. For example, a 10% NaCl solution has a density of 1.074, not 1.100. In general, the actual
concentration will be higher than what your incorrect calculation suggests.
Unfortunately, I don't think there is a simple and general way to calculate molarity based on the specific gravity of the solution, even if you have
complete information about the density of all the constituents. This is why they publish tables of data for some common chemicals (like ammonia or
NaCl).
| Quote: | | Therefore: 8.8 x 6.66 = 58.6grams of copper in 1 litre of the complete CUCL2 solution). |
Even if your approach were otherwise correct, this would be grams of CuCl2, not copper per se.
The less you bet, the more you lose when you win.
|
|
|
adamsium
Hazard to Others
Posts: 180
Registered: 9-4-2012
Location: \ƚooɿ\
Member Is Offline
Mood: uprooting
|
|
I noticed this, too - that the values were actually really solute masses and the mismatch in units. I also know that, in practice, the volumes do
change slightly (as I mentioned in my first post). I recall having read that the volume of an NaCl solution is generally approximately 2.5% less than
you'd expect it to be (which fits with your example, also). However, I was assuming the small difference would probably not matter much in this case
and wanted to save Chris the hassle of trying to find a table of densities for different concentrations. This probably isn't a great reference, but
it's interesting, nonetheless: http://www.eng-tips.com/viewthread.cfm?qid=217331
I'm also wondering if the reason for the confusion between density and dissolved salt mass was perhaps that Chris might have been reading something
that talked about using some sort of correctly calibrated / scaled hydrometer to easily determine the concentration of a given solution of a
particular solute.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
This is a quote from a pdf file that I have about the etching process. This section refers to Specific Gravity, With a special attention drawn to
the last phrase, ....copper concentration.
I Have Assumed then by this comment that he is referring to CU(0) Ie copper ions, because the rest of the multi page document refers to CUCl(1+) and
CUCl(2+) and HCl and H+ very specifically indeed.
<<<<<<<<<<<<Specific gravity is mostly dependent on copper concentration , and partly dependent on acid
concentration. The flat
plateau in the graph occurs when specific gravity in the range of about 1.200 to
1.400. This corresponds to a vary large variation in copper concentrations (sorry I
don't have numbers). I would not recommend operating at 1.200 or at 1.400, as
these values are getting too close to the plateau ends. According to a cupric
chloride technical document from Chemcut corporation , they recommend
optimum specific gravity to be between 1.240 to 1.330. This range lies about
directly in the middle of figure 2. For the hobbyist a safe range for specific gravity
may be between 1.22 and 1.38. This may sound like a small numerical difference,
but the physical change in copper concentration is quite large>>>>>>>>>>>>>>>
To sum up, I understand that volume and weight are two entirely different measurements, and that Density refers to well how Dense an object is, how
compact the molecular structure is, (I hope - just woken up)....and SG was explained to me as being the amount (density) of a specific ingredient
within a solution of other ingredients, that's how I have understood things from a lot of reading. This is not the same as concentration (moles)
because you can not measure the moles of copper ions in a solution, again this how I understood things from what I have been reading.
Also, when I was struggling to find out what on earth the SG of 1.3 and 1.4 represented, (otherwise they are just meaninless mumbo chinese numerics) I
came accross a sensible young man who said it in English without the high intellect attitude, he wrote: <<<<<<<The ideal
Specific Gravity of CUCl2 is between 270g and 360g per litre>>>>>>>.
and again this from another document (ignore figures, they are geared up for another process):
<<<<<<<<<Density (Copper Content) -- The initial operating density (specific gravity) is 1.17 grams/mL. Density will
gradually increase as copper dissolves into solution during etching, and as water evaporates>>>>>>>>>>>
So if all this is wrong then I'm lost
[Edited on 22-7-2012 by CHRIS25]
[Edited on 22-7-2012 by CHRIS25]
[Edited on 22-7-2012 by CHRIS25]
[Edited on 22-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
adamsium
Hazard to Others
Posts: 180
Registered: 9-4-2012
Location: \ƚooɿ\
Member Is Offline
Mood: uprooting
|
|
Well, it sounds like what I mentioned in my last post is somewhat correct. They're apparently using the specific gravity of the solution to determine
some other parameter.
I believe I've found the PDF to which you refer. http://jimlaurwilliams.org/projects/seychellePaper/index.htm... (at least this seems to be a .html version of it). I'd wondered what the graph of
specific gravity had been plotted against - it didn't seem to make sense that it would be molarity, obviously. Etch time makes much more sense. After
having a (very) brief look at this document, I really think that the best way for you to move forward is to get a hydrometer so that you can
accurately measure the SG of your solutions. I know you said that this was the problem initially, but I'm not sure that there's going to be another
simple alternative. Making up a solution with a SG between 1.200 and 1.400 (assuming this is actually the goal here) will be easy with a hydrometer.
They can be found inexpensively on ebay.
From the quick look I've had, there seems to be a lot of useful information in that document. I assume you've performed the suggested acid titrations
and such...?
I don't quite get your understanding of specific gravity. The specific gravity of a substance is simply the ratio of its density to the density of
water (at 4oC, apparently - i.e. when pure water has a density of 1.000 g/mL): http://www.ndt-ed.org/EducationResources/CommunityCollege/Ma... Density, on the other hand, is just the mass of substance per unit of volume of
that substance. The derived SI unit for density is kg/m3 (kilograms per cubic metre), though, this is not ideal for many applications, so
g/mL and such are frequently employed. So, if you have 100 mL of some substance (in any phase), and it has a mass of 250g, the density is 250
g/100 mL = 2.5 g/mL. This is 2.5 times the density of water (at 4oC) - because the SG of water is 1.00 g/mL, so it's specific
gravity will be 2.5. The apparent specific gravity, like density, will vary with temperature - just because the density of water might change by,
say, 0.2% for a given temperature change, doesn't mean that the substance of interest also will - so the temperature of both the substance of interest
and the water used for comparison must be the same (or corrected for). This is explained well by the wikipedia article on specific gravity.
Also, I'm not sure what you mean by Cu(0) ions. A neutral molecule or atom is not an ion. So, a copper atom with a 0 charge is a neutral atom and not
an ion. As I said, I've not had a thorough read of that document, but I do wonder if perhaps they're being somewhat inconsistent in their use of the
terms copper, copper(I) (cuprous) and copper(II) (cupric) - sometimes perhaps just using "copper" to refer to ions in solution rather than neutral
copper. I'm mostly referring to where it mentions "copper concentrations".
Sorry if this is not helpful and more confusing than anything. I do hope it's at least somewhat helpful, though.
|
|
|
bbartlog
International Hazard
Posts: 1139
Registered: 27-8-2009
Location: Unmoored in time
Member Is Offline
Mood: No Mood
|
|
1.24 to 1.33 is a big enough range for SG that you can get by with a graduated cylinder and a scale, I would think. Pretty concentrated solution,
though!
The less you bet, the more you lose when you win.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Ok Guys now I'm just getting muddled. By the way Adamsium, yes that was one of the many documents, and yes there is inconsistency in terminology and
that gets infuriating because one calculation can cause me days of headaches when one person substitutes a correct term for a subtle alteration in
language use, something I learned not to do years ago in English technical writing for a target audience.
Anyway: A hydrometer is an instrument used to measure the specific gravity (or relative density) of liquids; that is, the ratio of the density of the
liquid to the density of water. Wikpedia! Therefore why use that when I have just done exactly the same thing here: Ratio of solution to water was
1.05:1 (in my 158g sample which was 150ml in a beaker)? 1gr is approx 1mL as far as water is concerned and there is quite a large amount of water in
my solution. Therefore the there has to be 8g (very roughly) of something in my solution, and it is not the HCl because the H+ and the Cl is tied up
and attached to the CU, the H2O is also tied up in that the O is being evaporated. The only other thing is Copper? the chloride is not included as
a separate weight either, since that is attached to the copper as CU- and CU(2+) in solution, my 8g logically includes any CUCl or as I understand
it copper in solution and if the solution increases in copper concentration too much then etch rate decreases accordingly. This is how my logic is
running, if it is wrong then that is ok, I need to learn.
Now I am aware that my thinking might be childish, but it makes more sense for me to think in toddler concepts and then eat the meat of maths and
algebra, x's and y's once I understand the principle at work.
Yes sorry about the use of Cu(0) I saw that being used many times, what is meant is pure copper metal. So actually there is no pure copper metal in
solution since it is all tied up in various bonding, so I should have thought things out a bit more clearly there.
Also yes, titration is working fine, I thank amongst others watsonfawkes for his input, also weiming and a couple of others whose names I forget but
do recognise.
[Edited on 22-7-2012 by CHRIS25]
[Edited on 22-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
bbartlog
International Hazard
Posts: 1139
Registered: 27-8-2009
Location: Unmoored in time
Member Is Offline
Mood: No Mood
|
|
A hydrometer is quite a bit more convenient, and generally more precise, than measuring the specific gravity via volume and weight separately. For
your purposes I agree that it's unnecessary, but if (for example) someone is trying to determine the ethanol content of some fermented solution, they
might want to be able to reliably measure the difference between SG 0.991 (5% ethanol @4C) and SG 0.988 (7% ethanol). Getting that kind of precision
via graduated cylinder and scale requires good equipment and technique and is a bit of a pain in the ass, while doing it via hydrometer is easy as
pie. But your precision requirements look to be more than an order of magnitude less.
I can't really make heads or tails of your reasoning regarding the copper (and the non-contribution of chloride to increased density). But by way of
illustration, there seem to me to be two ways to look at the addition of a salt to water:
A) the volume of the salt and the volume of the water are added when they are mixed, so that the density of the resulting solution is just the
weighted average of their respective densities
B) the water takes up the salt without increasing in volume at all, so that the density of the solution is greater than that of water in accordance
with the mass of the added salt
I believe A) is generally closer to the truth, but that there is some reduction in volume (as noted by adamsium above) and corresponding increase in
density, so that the actual density ends up being somewhere between the lower value predicted by A) and the higher value predicted by B).
In the case of NaCl for example, we could look at the SG values predicted by the two models in a case where we added 10g of salt to 90g of water:
A) (adding volumes): 10g NaCl = 4.62 cc; 90g water = 90cc; final volume = 94.62cc; final mass 100g
Derived SG = 100/94.62 = 1.057
B) (no volume change): final volume of 90cc, final mass of 100g
Derived SG = 100/90 = 1.111
Actual SG of such a solution is 1.074 as noted above. Closer to A) but the molecules do 'fit together' better in solution and so the result is more
compact and slightly denser than simple volume addition would predict.
The less you bet, the more you lose when you win.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Hi bbartlog, yes, about the hydrometer I absolutely agree it is a necessity in this sort of measurement. I just reasoned that for this particular
situation, if I could achieve a satisfactory result without one then spending money was unnecessary because my measurements do not need to be precise,
that is not to say that I won't get one. If I had to be really precise then I would have to start taking into account surface area of exposed Copper
and thickness and I read about this and I tell you, It would be easier to learn the chinese language at a Russian school taught by a Swedish speaking
Indian.
The insight you gave above about the salt actually is good, I will bare that in mind. Sorry about the reference to the Chloride, I did actually mean
that the chlorid easpect also counts for the weight, when the PDF mentioned copper instead of Copper chloride I had a hunch that this could not be a
measurement of the Copper alone without any shall we say added attachments since this is improbable. Actually correct me if I am wrong but the copper
can not exist alone in the solution.
Thankyou for your imput. All answers go into a reference file of mine, a bit like a college folder really.
[Edited on 22-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
