Puzzled by aqueous solution terminology

In summary, this notation is used to indicate that the concentrations of the ions are not necessarily identical, but the solution still contains both ions.
  • #1
dgm
9
0
I'm just beginning to learn general chemistry, and I'm reading my textbook's chapter on aqueous solutions.

My question is, why do we term a solution of an ionic compound (like NaCl) like this:

NaCl(aq)​

instead of:

Na+(aq) + Cl-(aq)​

? Technically, when the sodium chloride is dissolved in water, the ions dissociate, and they are no longer the ionic compound "sodium chloride", they're just sodium and chloride ions floating in the water willy-nilly, right?



And then, what if you dissolved sodium chloride and potassium nitrate into the same water. Would you write,

NaCl(aq) + KNO3(aq)​

? How do you know that it hasn't become:

NaNO3(aq) + KCl(aq)​

?
 
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  • #2
dgm said:
why do we term a solution of an ionic compound (like NaCl) like this:

NaCl(aq)​

instead of:

Na+(aq) + Cl-(aq)​

The first notation suggests identical concentrations of Na+ and Cl-, the second suggests solution that contains both ions, but their concentrations are not necessarily identical. But don't pay too much attention to this - this is a simplified notation, and it is not necessarily precise/unambiguous.

Technically, when the sodium chloride is dissolved in water, the ions dissociate, and they are no longer the ionic compound "sodium chloride", they're just sodium and chloride ions floating in the water willy-nilly, right?

Yes.

And then, what if you dissolved sodium chloride and potassium nitrate into the same water. Would you write,

NaCl(aq) + KNO3(aq)​

? How do you know that it hasn't become:

NaNO3(aq) + KCl(aq)​

?

Technically it is impossible to find out what salts have been dissolved, which is why - especially in the case of natural waters - we give not amounts of salts dissolved, but concentrations of individual ions, this is unambiguous and precise.

If the solution was prepared by dissolving NaCl and KNO3 first notation suggests identical concentrations of Na+ and Cl-, and identical concentrations of K+ and NO3-, the second notation suggests something else. Again, don't treat the notation too religiously, it is often used in ambiguous way or even abused. When it matters, there are better ways of telling what we mean.
 
  • #3
Thanks. :)

Another question that's been bugging me lately: is it possible to isolate certain ions, so that they are not part of any compound? Like, would it be possible to manufacture a container of pure chloride gas, as opposed to chlorine gas?
 

1. What is an aqueous solution?

An aqueous solution is a solution in which water is the solvent. This means that the substance being dissolved, known as the solute, is dissolved in water.

2. What is the difference between a solute and a solvent?

A solute is the substance being dissolved in a solution, while a solvent is the substance in which the solute is being dissolved. In an aqueous solution, water is the solvent.

3. What does it mean when a substance is "dissolved" in water?

When a substance is dissolved in water, it means that the individual particles of the substance are evenly distributed throughout the water. The substance is broken down into smaller particles, called ions, which are surrounded by water molecules.

4. How is concentration measured in an aqueous solution?

Concentration in an aqueous solution is typically measured in moles per liter (mol/L), also known as molarity. This measures the amount of solute dissolved in a given volume of solution.

5. What is the difference between a dilute and concentrated solution?

A dilute solution has a low concentration of solute, meaning there is a small amount of solute dissolved in a large amount of solvent. A concentrated solution has a high concentration of solute, meaning there is a large amount of solute dissolved in a small amount of solvent.

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