Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: an3urysm on October 23, 2017, 11:41:55 AM
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Hi everyone.
I have a basic question. I know that when an ionic compound like NaCl is dissolved in water, it breaks down to Na+ and Cl- and yet it retains its properties like taste, smell etc. So I am guessing even if broken down completely Na+ and Cl- 'knows' they belong to NaCl.
But I m wondering what happens if multiple salts are dissolved in a single container, like both NaCl and KCl. We ll end up with 3 ions Na+, K+ and Cl-. But since they are completely disassociated, how does a Cl- ion in a water solution 'know' if it belongs to KCl or NaCl ?
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It doesn't. If you make up identical solutions from different starting materials, they don't "know" where they came from. For example, if you mix a 1M solution of NaCl with a 1M solution of KBr, you get exactly the same result as you do if you mix 1M NaBr with 1M KCl - a solution equimolar in Na+, K+, Cl- and Br- ions. No anions belong to particular cations, irrespective of how the solution was made.
It is misleading to say that a solid salt retains its properties when dissolved. (It doesn't retain its high melting point, for example, or electrical insulation.) The properties of an aqueous solution of NaCl are different from those of solid NaCl. (I presume that even the "taste" of salt is actually the taste of it dissolving in your saliva.)
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It doesn't. If you make up identical solutions from different starting materials, they don't "know" where they came from. For example, if you mix a 1M solution of NaCl with a 1M solution of KBr, you get exactly the same result as you do if you mix 1M NaBr with 1M KCl - a solution equimolar in Na+, K+, Cl- and Br- ions. No anions belong to particular cations, irrespective of how the solution was made.
Oh I see. So its just ions in a solution without belonging to a particular compound.
It is misleading to say that a solid salt retains its properties when dissolved. (It doesn't retain its high melting point, for example, or electrical insulation.) The properties of an aqueous solution of NaCl are different from those of solid NaCl. (I presume that even the "taste" of salt is actually the taste of it dissolving in your saliva.)
Ok my mistake. It does not retain all its properties. As you mentioned taste could be the taste after dissolving.
But I m wondering about 'some' properties which do extend to the aqueous solution too. What about properties like toxicity, color, etc ?
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But I m wondering about 'some' properties which do extend to the aqueous solution too. What about properties like toxicity, color, etc ?
Again, just like you confused taste as an intrinsic property of sodium chloride, when its actually a property of the ions, toxicity isn't a property that makes sense as something attached to a compound or ion. As for color, that can have nothing to do with the ionic makeup ... here's some extreme proof:
http://www.sciradioactive.com/radiation-effects/
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But I m wondering about 'some' properties which do extend to the aqueous solution too. What about properties like toxicity, color, etc ?
Again, just like you confused taste as an intrinsic property of sodium chloride, when its actually a property of the ions, toxicity isn't a property that makes sense as something attached to a compound or ion. As for color, that can have nothing to do with the ionic makeup ... here's some extreme proof:
http://www.sciradioactive.com/radiation-effects/
Ok. I went wrong again when I mentioned 'color'. Thanks for the link.
So what I understand from both of your replies is that the properties of an aqueous solution of an ionic compound depends on the ions rather than the parent compound. Am I right?
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That's the take home message. Your courses may start asking you to identify the properties of compounds, and you'll want to get it straight.
For taste, the way I'd heard it originally, was that the chloride ion binds to specific tongue receptors, therefore all chlorides have a salty taste -- NaCl, KCl with a bitter aftertaste, even HCl (very diluted and don't try this at home kids) along with other tastes. Alas,. I've since learned I had the concept backwards: Ref - https://en.wikipedia.org/wiki/Taste#Saltiness