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When you dissolve table salt (sodium chloride or NaCl) in water, are you producing a chemical change or a physical change? A physical change results in a change of the material's appearance, but no new chemical products result. A chemical change involves a chemical reaction, with new substances produced as a result of the change. When you dissolve salt in water the sodium chloride dissociates in Na+ ions and Cl- ions, which may be written as a chemical equation:

NaCl(s) → Na+(aq) + Cl-(aq)

Therefore, dissolving salt in water is an example of a chemical change.

If you search online for the answer to this question, you'll see about equal numbers of responses arguing that dissolving salt is a physical change as opposed to a chemical change. The confusion arises because one common test to help distinguish chemical and physical changes is whether or not the starting material in the change may be recovered using only physical processes. If you boil the water off of a salt solution, you'll obtain salt.

So, you've read the rationale. What do you think? Would you agree dissolving salt in water is a chemical change?

Sugar in Water - Chemical or Physical Change? | Chemical & Physical Changes

Comments

September 8, 2011 at 10:13 am
(1) Suzanne Breneman says:

I agree that dissolving NaCl in water is a chemical change. Do the ions then reassociate during the boiling process so that you get NaCl and water vapor?

February 12, 2012 at 7:32 pm
(2) Nicholas K says:

This answer is wrong. Dissolving salt into water is a textbook example of a physical change.

February 16, 2012 at 5:47 am
(3) Armida says:

WRONG. Salt dissolving in water is a physical change.

February 19, 2012 at 4:34 pm
(4) BOB Q says:

your all wrong
its a bunny change

February 24, 2012 at 11:27 am
(5) bergan says:

your right

April 29, 2012 at 6:44 pm
(6) Jimmy B says:

It is neither a chemical change nor physical change. In science education we like to classify things into black and white categories e.g. physical vs. chemical change, Solid vs. Liquid state of matter, living vs. non-living. In reality nature does not work like this. It is best to thing of these categories more as ends of a spectrum where some examples can hold properties of both. In this case dissolving of a salt holds properties of both a physical change and chemical change. To say it is one or the other does not describe the process properly.

May 1, 2012 at 6:30 am
(7) anor277 says:

The article is quite correct in classifying the dissolution of salt in water as a chemical change. Chemical change is characterized by the formation of new substances and the making and breaking of strong chemical bonds. Both processes occur when solid salt, an infinite array of close packed ions held together by strong electrostatic bonds, dissolves in water to give isolated sodium and chloride ions that are solvated by water molecules – these species, which exhibit ion-dipole interaction between the ion and the solvent, are manifestly chemically different from solid NaCl. The fact that this process is reversible is immaterial – many chemical processes are reversible.

If you are unconvinced, then consider the dissolution of copper sulfate in water. This is also a chemical change; it’s also one that occurs with a distinct colour change.

May 3, 2012 at 12:16 am
(8) Delany 110 says:

I disagree, because dissolving is a process in which substances mix uniformly with one another. A physical change is any change in size, shape, or state of matter in which the identity of the substance remains the same. Let’s say, you put a couple tablespoons of sugar in a glass of water, you let all of the sugar dissolve, but the question is, can you get the sugar back? Indeed you can, by simply allowing time for all of the water in the glass to evaporate, then at the bottom of the glass, you would be left with a type of milky, white substance, which is the dissolved sugar. The sugar is unchanged, even though it has dissolved, therefore most of the time dissolving is a physical process and change.

May 3, 2012 at 5:10 am
(9) anor277 says:

@delaney;

You are free to disagree. Nevertheless you have cited the wrong example in comparison. If you dissolve sugar in water or ethanol in water, you are NOT breaking any bonds, nor are you forming a NEW SUBSTANCE. These examples are indeed physical changes.

On the other hand, when salt is dissolved in water you ARE breaking the strong electrostatic bond between an sodium ion, and its 6 chloride ion neighbours. As above we often include the subscript “(aq)” when we dissolve something in water. What does this mean? It means the aquated sodium ion; quite probably an isolated sodium ion surrounded by 6 or so water molecules – held together by ion-dipole interactions – new chemical bonds formed between the sodium ion and the water molecules. The chloride ion which was quite obviously associated with the sodium ion in the solid state forms a separate aquated complex and is no longer associated with the sodium ion in solution. By my definition above this is clearly (and manifestly) a chemical change. In fact
in most of inorganic chemistry, one is often at pains to establish whether the structure of the solid state material (which can usually be determined very accurately) is the same as the solution structure (whose determination is often problematic). Solid state versus aqueous solution state NaCl is one example where the solution state and structure is quite different to the solid state. NaCl is also to some extent soluble in acetone. No colour change, but the cation in solution is [Na(O=C(CH3)2)6]+, a product of CHEMICAL change.

May 3, 2012 at 5:12 am
(10) anor277 says:

(contd from above)
Now take the example I cited before: the dissolution of anhydrous copper (II) sulfate in water. The solid copper salt is white; it dissolves water to give a lovely blue colour. What’s happened? We now have the aquated Cu(II) complex, [Cu(OH2)6]2+, blue in color, (and a distinct species to CuSO4), and some form of sulfate counterion, also aquated. The analogy to NaCl dissolution in water is obvious, but here no colour change is involved.

Some raise the objection that you get NaCl from crystallization of a NaCl solution; all this establishes is reversibility, and there are many examples of chemical reversibility. In fact the lattice enthalpy of solid NaCl is almost exactly equal to the hydration energy of sodium and chloride ions (i.e. the energy released when we form for example [Na(OH2)6]+ and [Cl(OH2)4-6]- (dissolution of NaCl in water is very slightly endothermic – and therefore the facile reversibility of the chemical reaction). If we use the right anion (maybe tetraphenylborate or some reasonably large anion) we could crystallize out these aquated complexes, and these solid materials would indeed represent the structure of [Na(OH2)6]+ in solution.

To conclude again, the making and breaking of chemical bonds and the formation of new substances are clear and unambiguous indicators of chemical change. Both processes occur when you drop common salt in water. This dissolution is therefore chemical by definition.

July 16, 2012 at 6:49 am
(11) ghail paras says:

it is chemical change!why? because the salt in the water melt right? therefore,it involves a chemical reaction.

August 30, 2012 at 10:19 am
(12) Dr JdT says:

This example has troubled me before… this is how I now rationalise it as a PHYSICAL change:

1. IMHO, chemical change is evidenced when new chemical bonds are FORMED [when reversibly forming a plasma - a physical change most of us would agree - the same chemical bonds do get broken and then later reformed]
2. dissolving NaCl in water does NOT lead to new chemical bonds being FORMED [sure ionic bonds are broken, bot no new ionic or covalent v
bonds are FORMED]
3. recall that intermolecular forces like ion-dipole interactions are not “proper” chemical bonds [I concede that dissolving anhydrous CuSO4 in water is (more of) a chemical change; I guess that H2O molecules forming stable octahedral complexes with Cu2+ are proper examples of chemical bonding....i.e. dative covalent bonds from a Lewis base to a Lewis acid?]

September 1, 2012 at 4:21 pm
(13) anor277 says:

@dr jdt;
What are proper chemical bonds? Ionic, covalent, almost certainly, why not ion-dipole (and of course we are being highly selective and prescriptive in defining a bond as ionic, covalent, metallic, or ion-dipole). The fact is that the ion-dipole bond is quite respectable from a thermodynamic perspective, some 400-600 kJ mol-1 (this is in aggregate for an isolated ion). By any consideration, these are proper (and real) bonds formed in the dissolution of an ionic solid.

From a chemical view, where in the solid state each sodium ion has 6 chloride nearest neighbours, whereas in solution it has (probably) 6 oxygen nearest neighbours, the case for designation as ‘chemical change’ is again compelling. And what if we dissolve the salt in ammonia, sulfuric acid, HF? New complexes clearly result.

September 1, 2012 at 4:23 pm
(14) anor277 says:

@dr jdt;
What are proper chemical bonds? Ionic, covalent, almost certainly, why not ion-dipole (and of course we are being highly selective and prescriptive in defining a bond as ionic, covalent, metallic, or ion-dipole). The fact is that the ion-dipole bond is quite respectable from a thermodynamic perspective, some 400-600 kJ mol-1 (this is in aggregate for an isolated ion). By any consideration, these are proper (and real) bonds formed in the dissolution of an ionic solid. And of course if such bonds were not formed, the salt would NOT dissolve.

September 1, 2012 at 4:36 pm
(15) anor277 says:

And ion-dipole bonds are not proper chemical bonds? In aggregate they are worth 400-600 kJ mol-1 (of ion). If these bonds did not form, or were insignificant thermodynamically, te salt would simply not dissolve in water.

September 2, 2012 at 10:00 am
(16) anor277 says:

Sorry for repeating myself. I will leave it up to the administrator to delete the superfluous posts.

October 11, 2012 at 4:47 pm
(17) Anon says:

You can get the salt back out of the water if you evaporate the water. Therefore, it is physical.

October 12, 2012 at 6:32 am
(18) anor277 says:

What is your point? Many chemical reactions are reversible, just like this one. Please read what is written earlier.

October 15, 2012 at 11:15 am
(19) Chem says:

I would like to call it a chemcial change wannabe, yet it is not a chemical change. Salt could be recovered by physical mean and therefore it is a physical change.

October 15, 2012 at 3:00 pm
(20) anor277 says:

And yet it is demonstrably and chemically different in the solution state as compared to the solid state. There seems to be some persistent confusion as to what chemical change is. Please read the definition above; the dissolution clearly meets the two criteria.

October 15, 2012 at 3:52 pm
(21) anor277 says:

And yet the chemical environment of NaCl in the solution state is clearly and demonstrably different as compared to the solid state. Some confusion seems to persist in the definition of chemical change, which is written above. The dissolution of NaCl in water clearly fulfills the criteria for chemical change.

October 16, 2012 at 6:54 am
(22) sdzxfcgv bn says:

Its both:
Physical: No longer the same thing, solid -> dissolved into solution.
Chemical: Bonds are broken, NaCl(s) -> Na1+(aq) + Cl1-(aq)

October 16, 2012 at 3:55 pm
(23) anor277 says:

The confusion continues. At least this time I should avoid repeating the same post.

October 22, 2012 at 5:24 am
(24) T.J. Kimani says:

its either physical because they can be retrieved back by a physical operation unit bt also it involves bond breaking making it chemical soo any is the right answer.

October 27, 2012 at 4:34 pm
(25) anor277 says:

@TJ read post 10; reversibility does not differentiate between physical and chemical change. While it’s never going to be a question that appears on an “AS” level paper, the dissolution is manifestly chemical.

October 28, 2012 at 8:55 pm
(26) S.Evans says:

I’d call it a state change (physical) rather than a chemical change. A chemical change is characterized by intermediate stages which aren’t apparent in simply saturating a liquid with a soluble chemical.

Now, add a reactive chemical, say metallic sodium, to the water and THEN you’ll see a real chemical reaction.

October 30, 2012 at 2:55 pm
(27) anor277 says:

“A real chemical reaction”, and real “proper chemical bonds”; we seem to have heard this complaint before, and the arguments have not been addressed by those who designate the dissolution as a physical change.

Well, I ask you to forget for the moment sodium chloride dissolution entirely, and consider the dissolution of anhydrous copper sulfate or anhydrous copper chloride. Is this a physical change as well? If it is, it is a physical change that proceeds with a notable colour change; yet colour changes often characterize chemical change.

November 18, 2012 at 12:04 pm
(28) Azhar mehmood says:

its physical change dear

November 24, 2012 at 7:34 am
(29) anor277 says:

Really, “dear”? Then you’ll have no problem arguing the case. Please do so; I am always willing to learn.

November 24, 2012 at 1:24 pm
(30) TYU55 says:

@Jimmy B

I agree with this explanation. There is no correct answer.

November 25, 2012 at 6:15 am
(31) anor277 says:

@TY, that’s the diplomatic answer. However, by the criteria I have advanced there is only one correct answer (which is not physical!).

No one has been been able to advance a compelling reason why we should designate the dissolution as ‘physical’. The conclusion is quite clear.

November 27, 2012 at 6:47 pm
(32) lilyrose says:

@anor calm down it is obviously a physical change

November 29, 2012 at 7:21 pm
(33) Jeff says:

Hi.
I have 2 questions, coming right now from a third grade teacher perspective, hoping to enlighten my students:

First, if there is a chemical change, as seems to be the case after reading all the comments, why does the water taste salty, instead of “sodiumy” or “chloriney”? Or is it one of those I’m tasting.

Second, anybody know what type of change it is when dissolving borax powder and getting it to crystallize?

Thx

November 30, 2012 at 3:05 am
(34) anor277 says:

@lr, I think I am quite calm. The problem is none of you can explain why the physical nature of this change is so obvious. This seems to be an area of chemstry that is very poorly understood.

November 30, 2012 at 12:44 pm
(35) anor277 says:

@Jeff, perhaps we’re trying to rationalize too much. Salt does taste salty, but before you can taste it, it has to go into solution on the tongue (as far as I know). Interestingly, both LiCl and LiBr have a salty taste.

In answer to your question regarding the dissolution of borax, since this is the dissolution of an ionic compound (albeit a hydrate), I would have to designate this a chemical change. In the solid state structure, the waters of crystallization solvate the boron rather than the sodium (and in solution of course, the added water solvates the sodium cations). But this requires a great deal of chemical sophistication on the part of KS3 or KS4 pupils.

December 11, 2012 at 10:24 pm
(36) Raymond says:

Physical changes require that a matter change state. Adding NaCl to water does not change it to a liquid state. Heating it to it’s melting point of 1474 degrees will. Adding NaCl to water does not change the state of water. Heating the water to 212 degrees will. Combining the two is a chemical change. Yes the process is reversible. You can separate the two forms of matter as well. This is also a chemical change. You are separating a solution into two different forms of matter (chemical change), not changing the entire state of the solution as a whole (physical change).

December 12, 2012 at 4:42 pm
(37) Robert Krampf says:

As with so many debates of this kind, the problem seems mostly to be in agreeing on the definitions of physical and chemical changes. The heart of both definitions seems to lie in their chemical formulas. If the formula for at least one of the substances changes, then most sources agree that it is a chemical change, while if the chemical formulas do not change, then most sources classify it as a physical change.

Beyond that, there is no absolute indicator that works. Color changes, gas bubbles, giving off or absorbing thermal energy, etc. MAY indicate a chemical change, but all of them can occur for physical changes as well.

Reversibility is a common misconception for physical changes. For example, brass is a solid solution of copper and zinc. Just as with dissolving sugar in water, there are no chemical changes. Now grab a piece of brass and reverse the process without resorting to chemistry. Let me know if you succeed.

On the other hand, many chemical changes are easily reversible. Use an electric current to break water into hydrogen and oxygen. A simple spark will reverse that, giving you water again, which can be broken down and recombined over and over. There are many “clock reactions” that reverse themselves over and over. These are definitely chemical changes.

With that said, I have to throw my hat into the chemical change side of this discussion. Breaking NaCl into Na+ and Cl- seems to be a change in the chemical formula to me.

December 13, 2012 at 3:58 pm
(38) anor277 says:

@RK, precisely! And not only are you breaking Na+/Cl- bonds; you are necessarily forming sodium ion water bonds and chloride ion water bonds (if these bonds did not form, the Na+/Cl- bonds would NOT break).

January 2, 2013 at 11:39 pm
(39) Maxy says:

This sounds like a case of theory of relativity. Another way to look at the issue is: does a solution of sodium chloride display chemical properties different from crystals of sodium chloride? How about simple taste test? Does aqueous solution of sodium chloride taste any different from crystals of sodium chloride? Is taste test a chemical or physical analysis? If two “different” substances has the same chemical property then their “difference” cannot be chemical but clearly physical. Irrespective of how we may look at breaking of bonds in crystal lattice of sodium chloride and formation of different bonds in the aqueous state the same ions are present in the two phases, in the same proportion and those ions retain the common taste of their coexistence. The difference in both phases is the physical states of the ions – period..Dissolution of a salt in which no new chemical substance is evident is obviously a physical change.

January 4, 2013 at 3:15 am
(40) anor277` says:

@Maxy. And is taste a solution or a solid-state phenomenon? I certainly don’t know, but I suspect the former. You write:

“Dissolution of a salt in which no new chemical substance is evident is obviously a physical change.”

You seem to have ignored the argument that the chemical substances in solution are quite distinct to the chemical substances in the solid state; they are clearly different chemical entities. C’est la vie.

February 8, 2013 at 10:32 am
(41) Testy says:

I disagree, dissolving NaCl in water is a physical change because the salt can be collected back through evaporation

February 9, 2013 at 5:25 pm
(42) anor277 says:

@Testy, you are certainly free to disagree. But read the rest of the thread. Reversibility does not differentiate between physical and chemical change. Many chemical reactions are reversible.

February 13, 2013 at 1:33 pm
(43) Chemistry PhD says:

Thanks Anor for your comments.

It’s a pity that in a lot of text books in primary and secondary school we still find this error.

Those of you who still are doubting about it, pay attention to Anor’s comments. Specially those who explain it is a physical change because the salt can be collected back. This is an antiquated and false concept.

Solvation of ionic compounds is defined as a chemical reaction by many dictionaries as the American Heritage Dictionary of the Collins, and as such, it can be represented with chemical equations.

http://ahdictionary.com/word/search.html?q=solvation

Precipitation of ionic compounds is just the reversed reaction.

So please, stop making unfounded and baseless comments that may confuse students.

February 13, 2013 at 5:33 pm
(44) josep says:

More examples of chemical reactions of solvation

NaNO3(s) → Na+(aq) + NO3-(aq)

(NH4)2SO4(s) → 2NH4+(aq) + SO4-2(aq)

Mg(NO3)2(s) → Mg+2(aq) + 2NO3-(aq)

NaCl(s) → Na+(aq) + Cl-(aq)

February 24, 2013 at 9:41 pm
(45) Lucidus says:

I strongly disagree that dissolving salt or sugar represents a chemical reaction. Chemical reactions require a new substance to be formed. Sodium ions don’t become elemental sodium as in a redox reaction. Water molecules also remain intact, simply surrounding the ions.
The ion does NOT form a new substance amid the molecular water. Solutions, Colloids & Alloys are classified as physical mixtures. Unlike a new substance formed in a chemical reaction, the alloy, solution or colloid, on a macro level, has intermediate characteristics and the components are physically separable.
The lovely blue color of copper sulfate in solution as a hydrated crystal “alloy” or an entirely dissolved salt is directly related to the copper metal ion and how it responds to “white” light as it is refracted by the water molecules surrounding the copper ion. If we evaporate the water, the refraction is gone and so is the color. We must remember that color is a photon energy released from an electron and captured in a chemical reaction on our retinas.
Solvation, the process of breaking the electrostatic attraction of ions by the polar molecules of water surrounding them, is physical change. Solvation can have a significant energy associated with it, but it is a physical action of dipoles and attractive/repulsive forces, not the formation of bonds. Consider how the Tyndall Test for solutions, colligative properties and Beer’s Law are all physical in their nature. We take water for granted because we live in a water filled place.
Think of water as a catalyst for ionic compounds that would not otherwise be reactive at room temperature because they would be frozen solid crystals… We can see Platinum as a catalyst or enzymes as a catalyst. They are physically involved in orienting the species to be able to form the activation complex – important to accomplishing the chemical reaction, but entirely in a physical manner.

February 26, 2013 at 10:09 am
(46) anor277 says:

At last a reasoned criticism, but I think you are incorrect. We are agreed that sodium ion is not reduced in water, but we disagree that [Na(OH2)6]+ is a de novo complex. Now you would agree that this is an entirely different species (and structure) to sodium ion in the solid state, where the sodium ion is surrounded by 6 chloride ligands. The bonds (non-directional, sure) are strong in the solid state. The bonds, in the solution state, to 6 aqua ligands, must be equally strong for the dissolution to occur (in fact they are almost precisely equal). Moreover the bonds that occurred in the solid state between sodium ion and chloride are completely disrupted. They are too independent species, as osmotic and other colligative properties clearly indicate. It is my opinion that the bonds between the aqua ligands and the sodium ions are real chemical bonds (our representations of ionic, covalent, metallic bonds, are all part of a continuum); of course they are, they are ion-dipole bonds, which are quantifiable and here thermodynamically strong. And if I dissolved the salt up in HF or ammonia, I would have a new set of ion-dipole complexes, say [Na(solvent)6]+, again the products of chemical change. By the definitions I have advanced above, bonds broken and new complexes formed, this is clearly a chemical change.

As regards the dissolution of anhydrous copper sulfate in water, you are even on shakier ground. I appreciate that colour is a transition associated with the copper ion. You should also appreciate that colour change is one the best indicators of chemical change; it always has been. Also here I would be quite justified in invoking covalent bonds between the oxygen donor of the aqua ligands and the copper base.

February 26, 2013 at 5:16 pm
(47) anor277 says:

Just to add that I never proposed that the dissolution of sugar represents chemical change (because no bonds are broken and no new substances formed). I also reject the analogy of water as a catalyst for ionic compounds. It’s hard to know what you mean precisely here. The aquated sodium ion in water is pretty well-known, and it’s pretty much divorced from the aquated chloride ion in solution. Sodium chloride could also be dissolved in ammonia ohydrogen fluoride to give differently solvated ions.

March 24, 2013 at 5:15 pm
(48) COYOTE says:

Dudes and/or dudettes, really fascinating stuff, I came here in search of what exactly (NH4)2SO3, or the ammonia portion of the compound was comprised of and got stuck in the middle of chemistry 107! again great-stuff! great comments and I for one, Appluad you’r scientific community..

April 9, 2013 at 7:36 pm
(49) Jarod says:

WRONG! It is a physical change! You made me get it wrong on my science homework!!! And I didn’t even do it in pencil so I could erase it. If I fail Year 10 Science, I blame you.

April 11, 2013 at 8:43 am
(50) anor277 says:

@Jarod, I take it you are being tongue in cheek. I have painstakingly detailed my reasoning. Have you considered the possibility that your teacher may be wrong? It has been known to happen; he or she might not even be a chemist.

May 1, 2013 at 5:13 am
(51) Lynette says:

I agree with the article and some people here. It’s neither chemical nor physical. But alas, I have to follow the text books, because it’s school and it ain’t smart to trash the curriculum. Why is it always considered as physical?

May 2, 2013 at 1:45 pm
(52) PhilF says:

It seems to me that if you define it as a chemical change you should be able to dissolve one molecule of NaCl in water and be able to divide the solution into separate parts and, at some point, have one cup containing only a sodium ion and another cup containing only the chloride ion. Not going to happen. Of course if you apply electrolysis you can get your truly chemical reaction to produce sodium metal and chlorine gas.

May 5, 2013 at 11:19 am
(53) anor277 says:

@PhilF, and if you take your one “molecule” of sodium chloride, what osmotic pressure is it going to exert? (My term would be formula unit instead of “molecule”. Again, there is no such thing as a true chemical reaction that excludes dissolution of ionic salts.)

May 13, 2013 at 8:59 am
(54) Nick says:

I would agree it’s a chemical change in that there is a rearrangement of the atoms and bonds. Salts are held together by ionic bonds and are breaking upon hydration to form ion–dipole forces with water. Yes, you can recover the salt by boiling off water, but again this describes a chemical change in that strong bonds are broken and then reformed.

June 5, 2013 at 12:48 am
(55) lololol says:

thank-you so much!!!!! this really helped with my homework!!!

June 7, 2013 at 3:29 pm
(56) David says:

As an 8th grade science teacher who needs to embrace some simplification, I’m wrestling with how to explore this with my students.

My problem is that melting is a classic example of a physical change. But if you melt solid NaCl, the Na+ and Cl- ions start to move around – meaning the ionic bonds between the ions break, just as they do during dissolution. So if we define a chemical change as anything that breaks an ionic or covalent bond, then the melting of NaCl is a chemical change as well. That’s consistent, but not neat.

What if we only define “chemical bonds” to mean covalent bonds? Well, then NaCl isn’t really a chemical compound; it’s a perfectly uniform solid “solution” of Na+ and Cl- ions. Not that different from ions dissolved in water, actually, just with stronger bonds. In that case, dissolving NaCl is a physical change, because breaking those bonds and replacing them with ion-dipole bonds is still not a chemical reaction, since none of the bonds involved are chemical bonds. But then we’re breaking all sorts of other rules by declaring that NaCl isn’t even a chemical compound in the first place.

The only thing I can find that works for me with consistency and avoids these problems is to declare that Na+ (s/l/g) and Na+ (aq) are different things, since the Na+ (aq) have hydration sphere bubbles around them that keep them from interacting with their Cl- neighbors. Maybe we should simply write Na+ (aq) as Na(H2O)6+ to make that more clear – in other words, declare that strong ion-dipole bonds are strong enough to be worthy of a chemical formula. Then everybody would agree that NaCl (s) + 12H2O -> Na(H2O)6+ + Cl(H2O)6- was a chemical reaction. Of course, the problem with that is there’s no guarantee there will be exactly 6 water molecules surrounding each Na or Cl ion, and no good way to determine how many there WOULD be.

June 10, 2013 at 1:39 am
(57) anor277 says:

@David, it is relatively difficult to introduce the distinction at KS3(?) level, nevertheless the dissolution (as opposed to ‘melting’) of sugar in water is fundamentally different to the dissolution of salt; the former is a physica change; and you know my views on the designation of the latter dissolution. I probably would be in favour of making the distinction between salt and sugar dissolution quite early on. (But how to test this? Maybe a simple osmosis experiment?)

As you have proposed, I would stress the importance of the (aq) subscript, to represent the “aquated” sodium ion in solution. In transition metal chemistry, when we deal with Cu2+(aq) or Fe2+(aq) we know precisey what we’re dealing with. As regards to the problem you identified, the aquated ions might be 4 or 5 waters sometimes, but the evidence (crystal structures of salt) of hydrated sodium ions always points to 6 waters (this difference in solid versus solution structures is widespread in most of structural chemistry – it’s a very familiar problem.

June 26, 2013 at 5:26 pm
(58) Johnny says:

This is a PHYSICAL change. This is incorrect.

June 28, 2013 at 3:01 pm
(59) anor277 says:

@Johnny, can’t help you much unless you read the remainder of the thread.

June 30, 2013 at 5:44 am
(60) anukriti singh says:

WRONGGGGGGGGGGGGits oviously a physical one because no new substances are formed in it …….and this experiment is also reversible…

June 30, 2013 at 3:52 pm
(61) anor277 says:

Another individual who has not even read the thread. (i) reversibility does not differentiate between chemical and physical change. Many chemical reactions are reversible, and a few physical reactions are irreversible. (ii) The aquated sodium in aqueous solution is surrounded by 6 water molecules; this is clearly a different chemical entity to the solid sodium ion in sodium chloride that is surrounded by 6 chloride ions. I hope this is the last time I have to repeat myself.

July 21, 2013 at 8:10 am
(62) frank says:

What difference does it make? In 7th grade I was marked wrong for saying that baking a cake was a chemical change. The teacher said “It’s not like you burn it down to carbon” — but now I know about the denaturing of protein, and I could have told him that. But what difference does it make? The only important thing is to understand what is going on, and few people even understand what is going on with salt. For example, have you ever tasted nonaqueous salt? No, because by the time it is on your taste buds, it is an aqueous solution — o bonds, just ions.

September 13, 2013 at 9:58 pm
(63) nec says:

An interesting take on a debate that seems to be taking over the scientific corner of the internet. Unfortunately, I’m going to have to side with the physical change-ers. Chemistry is concerned with the transfer of electrons; it’s what the study of chemistry is all about. You could cite Bronsted acids and bases and talk about proton donation, but that’s just an easy way to conceptualize a difficult process that has to do with electron transfer. The way electron transfer plays out is in the making and breaking of bonds. Now I’ve seen a bunch of comments where you’ve made the argument that dissolving salt in water does, in fact, break bonds; but strictly speaking, the bond between the cation Na+ and the anion Cl- is solely based on electrostatic attraction. In other words, before the bond was even formed, the Cl “stole” the electron from the Na. What does this mean for the purposes of this argument? Basically, when we dissolve NaCl, we’re not doing anything to the electrons – the chloride stays ionized, meaning it retains the electron it took from the sodium. In other words, the chemical process that formed the bond from pure sodium and chloride is NEVER UNDONE when we dissolve NaCl; the attractive force is still there; it’s just being “outweighed,” so to speak, by other forces. Since electrons are never transferred, we can’t say that any chemical change has taken place. So it’s a physical change.

September 13, 2013 at 9:59 pm
(64) nec says:

(continued)
There are other arguments to make – the argument that aqueous sodium chloride is still classified as aqueous sodium chloride in chemical equations, indicating that the scientific community’s operational definition for this is a physical change (state changes are physical) comes to mind. But I think the strongest in favor of physical change is the aforementioned electron transfer argument.

A final observation: do a quick google search if you would, Ms. Helmenstine; the rest of the internet, including numerous scientific websites, is against you. Not to be fallacious, I’m not saying this makes you wrong; you just might want to be willing to rethink the way you define chemical changes.

September 16, 2013 at 9:53 pm
(65) cation5 says:

Thank you, anor277, for a most eloquent and correct answer to the question. Your patience with the unknowing is also commendable!

September 19, 2013 at 8:46 pm
(66) Irena says:

It’s undergoes a physical change not chemical!

September 24, 2013 at 7:57 pm
(67) ckdwn says:

dissolving is physical change

September 27, 2013 at 10:53 am
(68) anor277 says:

Again, there are a series of comments that claim that dissolution of salt is not a chemical change. Some have tried to address the arguments I advanced beforehand.

1. The claim that electron does not take place during the dissolution cannot be supported. Electron transfer does take place. Electrons (on the oxygen molecule) interact in an ion-dipole fashion with the sodium ion. This interaction is real, thermodynamically strong in aggregate, and at the limit we could call the resultant complex a coordination complex; which brings me to the second point.

2. An electrostatic bond is a ‘real’ chemical bond, a bond that is demonstrably broken in the dissolution process. Going back to the first principles of Chemistry, we draw the bond-triangle, ionic, metallic, covalent. If the salt was AgCl, water could not break this bond, however, ammonia could do so to give a different solvato complex.

3. The claim that we write NaCl<sub>(aq)</sub> is immaterial. So what? It is merely a shorthand. We mean Na<sup>+</sup><sub>(aq)</sub>, an ion-dipole complex that is characterizable and certainly distinct from the solid state structure.

September 27, 2013 at 10:55 am
(69) anor277 says:

4. As to the claim that the majority of sources on the internet claim that this is a physical change, this is simply argument from popularity, and therefore fallacious. If a majority of Inorganic Chemists claimed that the dissolution was physical, you might have more of a point, but I can assure you that this is not the case. (If you don’t believe me canvas the opinion of a professor of Inorganic Chemistry.)

In summary, strong chemical bonds are broken in the dissolution, and strong chemical bonds are afterwards made in the new substances that are formed. It is ludicrous to suggest that the aquated sodium ion has the same chemical environment as the sodium ion in solid state sodium chloride. These manifestly fulfill the criteria for chemical change.

October 1, 2013 at 3:31 am
(70) anor277 says:

Just to recap, it was earlier suggested that NaCl dissolution could not be designated chemical because electron transfer did not take place (this of course ignores the electron density that sodium ion mobilizes in the ion-dipole interaction with water). As another illustration of the weakness of this argument, consider the precipitation of an ionic solid. When silver ion interacts with chloride ion formal electron transfer has in fact taken place at some time in the past. Nevertheless, when silver and chloride ions meet a curdy white precipitate of AgCl deposits (the lattice enthalpy of this solid is too large for a water dipole to disrupt). So if the former argument is true, and we cannot designate the dissolution of NaCl as chemical, then by the same reasoning we cannot designate the formation of AgCl from aqueous ‘silver nitrate’ and ‘sodium choride’ as chemical. This stretches credulity quite a bit.

It is remarkable that in this long thread we have had many adherents of the counter view (that NaCl dissolution is physical) baldly state that of course the dissolution is physical. Very few have brought one thing to the table by way of argument or evidence. They cannot even qualify what they mean by physical or chemical change. It seems that the nature of chemical change is quite poorly understood and people will repeat what they may have wrongly learned as students without thinking about the matter. My own argument has been careful to qualify the nature of chemical change. To repeat it (again!), chemical change is characterized by the making and breaking of strong chemical bonds, and by the formation of new substances. I doubt that it is possible to argue that the formation of aquated sodium and chloride ions from a solid lattice of NaCl does not fall under this umbrella.

October 16, 2013 at 6:41 am
(71) kyari says:

I agree that there is a chemical change in this experiment……….
(Dissolving is a chemical change).

November 4, 2013 at 5:56 pm
(72) skin im in says:

ITS A CHEMICAL CHANGE!

November 12, 2013 at 9:26 am
(73) Samantha says:

WRONG it is chemical change

November 16, 2013 at 9:59 am
(74) melissa samuelson says:

Dissolving salt in water is a physical change. The salt and water keep their original properties. You can still taste the salt in the water. The fact that it dissolved is the property of solubility which is a physical property.

November 16, 2013 at 1:56 pm
(75) anor277 says:

@melissa_s… Just saying something does not make it true. I cannot help you much if you are unwilling to read the remainder of the thread.

December 21, 2013 at 11:55 pm
(76) Sai Rahul says:

ITS A CHEMICAL CHANGE!

March 5, 2014 at 12:41 pm
(77) zain mobeen says:

wrong by a text book it is a pysical change

March 29, 2014 at 4:20 pm
(78) Richa says:

Dissolving salt in water is a physical change as no new substance is formed. Sodium and chloride ions already existed even before the salt was mixed with water. Salt is an ionic substance and therefore does not exist as discrete molecules.Water just separates the sodium and chloride ions further apart from each other. Definitely, the interaction between the ions ( sodium and chloride ions) now changes from ionic bond to ion-dipole interaction ( water is polar molecule with a slight positive charge hydrogen atoms and slightly negative charge on oxygen atom). Do you think this can be classified as chemical change?

April 1, 2014 at 2:49 pm
(79) anor277 says:

@Richa. not only do I think that dissolution of salt in water can be classified as chemical change, I have painstakingly detailed my reasons for doing so here. Try reading the thread. An isolated sodium ion in the solid state is surrounded by 6 chloride ions. In aqueous solution that same sodium ion is surrounded by 6 oxygen donors.

April 11, 2014 at 4:31 pm
(80) Einsteinium says:

All of the classical examples of physical change include: cutting wood, pouring a glass of wine, a rain puddle evaporating, and snow melting –can you write a chemical equation for any of the above events, as you can with the combination of water and salt, where there is a distinction between the reactant and product?

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